Contents Popular Astronomy | Fall 2017 | Volume 1, Number 1
From the Editor On the History, Legacy, and Return of Popular Astronomy
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John Schroeter, Editor in Chief
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Guest Editorial Why Do Astronomy?
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By Dave Finley
History of Astronomy A Privileged View of the Stellar Universe
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By Dava Sobel
The History of Uranography |
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By Wil Tirion
Music and the Making of Modern Science
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By Peter Pesic
Events Totality! The Solar Eclipse of August 21, 2017
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By Jeffrey Bennett
Exoplanets The Planetary Zoo
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Exploring the Astounding Diversity of Exoplanets
By Michael Summers
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Extrasolar Planets and the Cosmic Perspective
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Observing Nebulae |
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By Martin Griffiths
Quitting the Day Job
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By John Read
Seeing in the Dark By Brenda Tharp continued
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By Jeffrey Bennett
Astrophotography
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Contents
continued
Popular Astronomy | Fall 2017 | Volume 1, Number 1
Telescopes
The Next Telescopes |
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By Geoff Cottrell
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134
Experiencing Space
Space Tourism: Now and in the Near Future |
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By Neil F. Comins
Community Check It Out!
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A Blueprint for a Library Program in Astronomy
By John Fossett
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Radio Astronomy Galactic Quests | 134 Powering Astronomy’s Quest for Fleeting Radio Frequency Bursts from Beyond our Galaxy
By John Schroeter
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Astrophysics Einstein’s Castle in the Air
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GET
146
By George Musser
Link references throughout this magazine: Website link
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From the Editor | John Schroeter
On the History, Legacy, and Return of Popular Astronomy By John Schroeter, Editor in Chief
H
ello and welcome to this special edition of Popular Astronomy. While we certainly hope you’ll enjoy our mix of articles, we especially hope you’ll feel welcome to participate. Over the coming
months we will present many opportunities for your involvement, and through those events, get to know you. Astronomy is one of the few sciences where amateurs continue to play a vital role. And Popular Astronomy—launched in 1893—is the magazine that started it all, igniting the amateur astronomy movement that is once again resurgent. But before we look too far forward, we’d like to spend a moment here reflecting on the title’s remarkable legacy—a legacy that we will work hard to both honor and advance. Founded by William Payne, Popular Astronomy was not
only astronomy’s first successful trade publication, it also served for many years as the unofficial journal of the AAS, and consistently attracted the field’s leading lights with articles that served as valuable references for professionals and sources of inspiration for amateurs. One of the most interesting aspects of the magazine’s content was its unusual practice of “. . . combining articles of technical merit with those in simpler language”—a trait that was much appreciated in the astronomical literature and an editorial tradition that we’ll continue.
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From the Editor | John Schroeter
On the occasion of Popular Astronomy’s 50th anniversary issue in 1943, many of astronomy’s foremost personalities offered their congratulations, along with their observations about the magazine’s importance and its influence on the field. For example, Leon Campbell of Harvard College Observatory wrote; As one who has followed with interest the career of POPULAR ASTRONOMY for over 40 years, I can frankly state that I have always considered the columns of the magazine as fulfilling the needs of both professional and amateur in every way. Harlan Stetson of MIT contributed; This magazine has filled a very distinctive and unchallenged place in the field of astronomical literature. . . This periodical has made an important contribution to the rise of astronomy in the United States, and it well deserves the recognition and esteem in which it has been held throughout the astronomical world. Emphasizing the role of amateurs, N. T. Bobrovnikoff of the Perkins Observatory wrote; POPULAR ASTRONOMY, through its 50 years of publication, has been an excellent medium for the dissemination of astronomical facts and theories—not only for the professional astronomer but for the amateur as well. In no other science is the work of the amateur as important as in astronomy. Whether it is in the discovery of novae or comets or in systematic observations of variable stars or meteors, the amateur has contributed greatly to our understanding of the universe. Because POPULAR ASTRONOMY is one of the few scientific publications available to the professional and the amateur alike, may it afford within its next 50 years an even closer bond of thought exchange that will be increasingly beneficial to both groups.
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From the Editor | John Schroeter
Dr. Oliver J. Lee of the Dearborn Observatory, who in 1930 offered evidence that the moon had been torn loose from what is now the basin of the Pacific Ocean, said; No astronomical publication exists, to my knowledge, which has for so many years served as a liaison medium between the interested layman or amateur and the professional astronomer. Between the very technical journals and the smaller publications which are issued more or less for the hit and run reader, the wide and interesting middle ground signals to POPULAR ASTRONOMY to continue its mission with high courage. There were 45 such contributions to that milestone issue, and we’ve included just a sampling here. We’ll close with what might be the most poignant of them all, by Ida Barney of Yale University Observatory, writing in the wartime of 1943: In these days of global war when science must necessarily be devoted chiefly to the development of instruments of destruction, it is pleasant to look back to peaceful days when scientific research could be pursued for its own sake and to hope that such days will return before POPULAR ASTRONOMY is much older. Sadly, though, Popular Astronomy didn’t get much older. In 1951, the magazine’s third editor, Curvin H. Gingrich, passed away after 25 years at the helm. He was 70 years old, and while retiring from more than 40 years of teaching, he had planned to continue as the magazine’s editor. But without an associate to carry on, publication ceased with the December 1951 issue. Charles Federer, who in 1941 founded Sky and Telescope at Harvard College Observatory, attempted to rescue Popular Astronomy—his chief competitor—by brokering its sale to Rensselaer Polytechnic Institute. The sale, however, was not consummated, and
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From the Editor | John Schroeter
Federer ultimately fulfilled the magazine’s balance of prepaid subscriptions with issues of Sky and Telescope—to this day, an outstanding and indispensable resource for astronomers. Fast-forward 58 years to 2009—the 400-year anniversary of Galileo’s invention of the telescope. In that landmark year, we announced our plans for the return of Popular Astronomy, along with our two other titles, Popular Electronics and Mechanix Illustrated (all three of which are now hosted at our TechnicaCuriosa.com hub). In 2009, however, the unstable state of a changing publishing industry conspired with an economic crash to effectively quash any plans for realizing the larger vision that we’re finally able to unveil today with this special edition. But such challenges never dampened our enthusiasm about the future of humanity’s oldest science and the small role we hope to play in it. While the world may be getting smaller, the universe just keeps on expanding, and that means the most exciting discoveries still lay ahead. We have no idea if the new Popular Astronomy will be around to celebrate its 50-year anniversary, but if we’re so lucky, we’ll hope to have earned accolades like those of our predecessors back in 1943. And should it continue, it will be, in no small part, thanks to the young would-be astronomers we inspire today through these very pages. There are many intriguing stories contained within this issue, and for that we owe our generous contributors a tremendous debt of gratitude. Each of them testifies to the essential role that professional astronomers play in a “popular” title such as this—a role that is, in fact, the key to fulfilling both the legacy and promise of Popular Astronomy. To these ends, we hope you will join us. In the meantime, thank you for spending a bit of your time with us here and at www.popularastronomy.com. From astronomy news to archaeoastronomy, astrophysics to cosmology, radio astronomy to backyard stargazing, space exploration to celestial mechanics, if it’s out of this world, our aim is to bring it within your view.
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Guest Editorial | Dave Finley
Why Do Astronomy? By Dave Finley, National Radio Astronomy Observatory
T
oday’s astronomers have the most powerful array of research tools in the history of the science, with high-tech telescopes on the ground and in space that cover the entire span of electromag-
netic radiation from radio’s long waves to high-energy gamma rays. The purpose of these advanced tools is to do fundamental research on the nature of the universe in which we live. This research seeks to answer some of the biggest questions we can ask, such as how did the universe begin (or did it begin), how big is it, how old is it, and how will it end (or will it end)? As the science that provides the framework knowledge of where we, and the planet on which we live, fit into the environment of the universe, astronomy is a vital part of the culture of all humanity. A person deprived of the broad outlines of astronomical knowledge is as culturally handicapped as one never exposed to history, literature, music, or art. As astronomers communicate new discoveries about the universe, they enrich the intellectual lives of millions. From the dawn of civilization, astronomy has provided important stepping stones for human progress. Our calendar and system of timekeeping came from astronomy. Much of today’s mathematics is the result of astronomical research. Trigonometry was invented by Hipparchus, a Greek astronomer. The adoption of logarithms was driven by the needs of astronomical calculations. The calculus, the basis of all modern science and engineering, was invented by Sir Isaac Newton for astronomical calculations. Astronomy provided the navigational techniques that allowed sailors and aviators to explore our planet and today
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Guest Editorial | Dave Finley
allow spacecraft to explore our solar system. Astronomy’s appetite for computational power drove the development of many of the earliest electronic computers. The space age, which brought us the communication and weather satellites upon which we depend each day, would have been impossible without the fundamental knowledge of gravity and orbits discovered by astronomers. Radio astronomers led the development of low-noise radio receivers that made possible the satellite communications industry. Image-processing techniques developed by astronomers now are part of the medical imaging systems that allow non-invasive examination of patients’ internal organs. At today’s observatories, the needs of astronomers for better instruments continue to drive developments in such diverse fields as electronics, mechanical engineering, and computer science. Astronomy has much yet to contribute to human knowledge and progress. From the airplane to the transistor, from radio to lasers, developments that transformed our society were based on fundamental knowledge of the physics of matter and energy. Astronomy offers scientists
Credit: NRAO/AUI/NSF
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Guest Editorial | Dave Finley
from a wide range of backgrounds with a nearly infinite variety of cosmic “laboratories” for observing physical phenomena. It is unlikely that any laboratory on Earth will ever produce matter as dense as that of a neutron star, temperatures as hot as those inside a supernova explosion, or gravity as strong as that of a black hole. Yet astronomers can study the physics of such extreme conditions routinely with their telescopes. Closer to home, continent-spanning radio telescope systems are a primary tool for providing valuable data on the drift of Earth’s continents, the workings of earthquakes and volcanoes, and the mechanisms of global climate. What will this yield? It is the nature of basic research that we can’t predict what will come of this work, except that we probably will be surprised. When Kepler and Newton labored to develop the science of orbital mechanics, they weren’t thinking of weather satellites or broadcasting from space. Finally, astronomy performs an important educational service for our nation. As an exciting, visual science easily accessible to amateur observers, astronomy stirs scientific curiosity in thousands of young people every year. These young people soon learn that astronomy involves nearly the whole range of the physical sciences, including mathematics, physics, chemistry, geology, engineering, and computer science. Many professional scientists in these and other fields first became interested in their profession through astronomy. In today’s world marketplace, a competitive nation needs for its entire population, not just its scientists, to have a basic level of scientific literacy. Astronomy, by providing the excitement of new knowledge about the fascinating variety of strange objects in the universe, can help communicate much basic science to all our people. In sum, astronomy has been a cornerstone of technological progress throughout history, has much to contribute in the future, and offers all humans a fundamental sense of our place in an unimaginably vast and exciting universe.
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History of Astronomy
T
rue to its name, Popular Astronomy magazine interpreted all the exciting developments in stellar and
planetary studies for a curious public, from the 1880s into the mid-20th century. “Terse and plain� were the bywords of farsighted founding editor William
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History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv Wallace Payne (1837-1928), who perceived a need for a non-technical magazine to satisfy “persons ... in every vocation of life, that have a love for this great science.” Payne, a professor of astronomy at Carleton College in Northfield, MN, and also director of the Goodsell Observatory there, borrowed the publication’s first title from Galileo. He called it The Sidereal Messenger. After supervising a successful decade in print, 1882 to 1892, Payne partnered with rising star George Ellery Hale (18681938), and changed the magazine’s name to Astronomy and Astrophysics. The hybrid tried to address professional and amateur astronomers alike, but within three years, when the co-editors deemed their mission too large, they divided the territory: Hale founded The Astrophysical Journal, in which established researchers reported their results; Payne returned to his original idea of disseminating information of interest and aid to amateurs. Although Payne’s new Popular Astronomy aimed at an amateur audience, astronomy professors and professional observers from all over the world contributed articles. They wrote willingly— and without payment. Appreciative readers praised the magazine for forging a link, not only between professionals and amateurs, but between astronomers in disparate and increasingly specialized fields. In the course of researching and writing my book The Glass Universe, I paged through the complete archive of Popular Astronomy held at the John G. Wolbach Library of the Harvard-Smithsonian Center for Astrophysics. The magazine’s early issues coincided with the same major changes in astronomy that were central to my story, such as the systematic application of photography to the problems of mapping, classifying, and judging the brightness of the stars. Many of my characters at the Harvard College Observatory were Popular Astronomy authors. I mentioned the magazine half a dozen times in my book. Like the Harvard Observatory, Popular Astronomy provided some unusual employment opportunities for women in the 1890s. Professor Payne, who
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History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv owned, published, and edited the magazine, chose Charlotte R. Willard, a Smith College graduate working as an assistant at the Goodsell Observatory, to be his associate editor. The name C. R. Willard appeared alongside that of Wm. W. Payne under the rubric “Editors” on the front cover of the September 1893 issue, while Payne’s daughter, Jessie V. Payne, oversaw the magazine’s business affairs. Many more women worked at the Harvard Observatory, where Williamina Fleming headed a female staff of some 20 computers and assistants. Mrs. Fleming had begun her Harvard career as a domestic servant for director Edward Pickering, but he soon moved her into the observatory and let her advance as far as her wit and skill would take her. As curator of astronomical photographs, she became the first woman ever to hold a Harvard University title.
Mrs. Fleming removed each glass plate from its kraft paper sleeve without getting a single fingerprint on either of the 8" x 10" surfaces. The trick was to hold the fragile packet by its side edges between her palms, set the bottom—
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j The dome of the
Great Refractor dominated the appearance of the Harvard College Observatory in the 1870s. A smaller telescope was mounted in the west wing.
History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv the open end—of the envelope on the lip of the specially designed stand, and then ease the paper up and off without letting go of the plate, as though undressing a baby. Making sure the emulsion side faced away from her, she released her grip and let the glass settle into place. The wooden stand held the plate in a picture frame, tilted at a 45-degree angle. A mirror affixed to the flat base caught daylight from the computing room’s big windows and directed illumination up through the glass. Mrs. Fleming leaned in with her magnifying loupe for a privileged view of the stellar universe. She had often heard the director say, “A magnifying glass will show more in the photograph than a powerful telescope will show in the sky.” In mid-August 1898, when Pickering invited distinguished astronomers to Harvard to discuss the formation of a national professional society (later named the American Astronomical Society), the Popular Astronomy reporter in attendance singled out Mrs. Fleming for special mention.
Everyone came, from Simon Newcomb, the elder statesman of the science, to 30-year-old George Ellery Hale. Hale, who so successfully organized the country’s first astronomy meeting in Chicago in the summer of 1893, had hosted another one in 1897, at the dedication of the grand new Yerkes Observatory in Williams Bay, Wisconsin, where he was now director. His arrival in Cambridge in 1898 coincided with a severe heat wave that lasted throughout the three-day gathering. Pickering’s welcome proved equally warm. As the attendees were too numerous to be accommodated en masse in the observatory, the director ushered all hundred-plus of them into the parlor of his home. “The spacious mansion of Professor Pickering formed an ideal place for the meeting of a convention,” writer Harriet Richardson Donaghe reported in Popular Astronomy, “while the gracious dignity of the director and the hospitality of his stately wife, who received their guests with a cordial greeting, gave the serious purpose of the assemblage a touch of festivity and saved even the
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j Mrs. Fleming
(standing at rear) earned a supervisory role over the other female computers and also a coveted Harvard title as curator of astronomical photographs.
History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv
j Pickering poses at
j Stars appear as black
non-scientist from feeling out of his element.” Miss Donaghe herself was one of the few non-scientists present. The situation called dots in this negative plate of to her mind Walt Whitman’s poem about the “Learn’d Astronothe Small Magellanic Cloud, a satellite galaxy of the Milky mer,” and she quoted part of a line from it in her article: “‘Charts Way that can be seen from and diagrams, to add, divide and measure,’ gave evidence of the the Southern Hemisphere. heavy work laid out for the savants, but behind them gleamed The splotch at right is the the snowy outlines of dense globular cluster of the bust of some honstars known as 47 Tucanae. ored ancestor, the rich coloring of a family portrait, or the sparkle of a jeweled miniature, in the artistic setting of a private drawing room.” Members of Harvard’s own observatory staff peopled the roster of speakers, beginning with Professor Searle, who delivered a talk on the “personal equation,” or the way an individual observer’s visual acuity,
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the entrance to the Brick Building with the female staff, ca. 1911. Margaret Harwood is at far left, Arville Walker just in front of her. Ida Woods stands at far right in the front row. The white-haired lady on the step behind her is Florence Cushman. At her right is Annie Cannon, and Evelyn Leland is in the back row between them.
History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv
j In a typical work
session, Miss Cannon would write numbers next to all the spectra on a plate, then call out each number and also her judgment of its spectral type to a recorder who wrote down her pronouncements.
eye-hand coordination, and speed of reaction affected his perceptions. Mrs. Fleming prepared an announcement of the numerous new variables with bright hydrogen lines found on Bruce and Bache telescope plates from Arequipa. The director read her paper aloud at the podium, adding a coda of his own. As Miss Donaghe reported, “In conclusion Professor Pickering said that Mrs. Fleming had omitted to mention that of these seventy-nine stars nearly all had been discovered by herself, whereupon Mrs. Fleming was compelled by a spontaneous burst of applause to come forward and supplement the paper by responding to the questions elicited by it.” The above-mentioned Bruce telescope, custom-built for Harvard’s southern station in Arequipa, Peru, had been the gift of New York heiress Catherine Wolfe Bruce. When she died at her home on March 13, 1900, Popular Astronomy regretted her passing.
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History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv “It is no easy thing to choose fitting words to refer to the close of any life on Earth,” editor William W. Payne of Popular Astronomy wrote in his obituary notice, “much more is it difficult to offer a right and worthy tribute to the memory of one like Miss Catherine Wolfe Bruce, who, for noble cause, the world of science has learned to love for what she was and for what she did.” Payne, whose own observatory at Carleton College in Minnesota had once received aid from Miss Bruce, praised “her intelligent generosity,” which “knew no limits of race or country, and so science the world over mourns a common loss. Her kind and thoughtful care lightened many a burden in her own land, awakened new zeal in needful research, and helped to finish many a task when patience and other resources were nearly gone.” In closing his brief sketch of her life, Payne itemized the long list of her gifts to astronomy. They totaled more than $175,000. Popular Astronomy not only reported the news; its editors often influenced astronomical practice. For example, Herbert Couper Wilson (1858-1940), who took over as top editor following Professor Payne’s retirement late in 1908, suggested a means for pooling the individual efforts of amateur observers.
Pickering’s volunteer army of variable star observers blanketed the Northeast by 1911 and extended as far west as California. There was even an outlier in Australia. Faculty and students at New England colleges such as Amherst, Vassar, and Mount Holyoke participated energetically in the routine observations. Strong foreign support arrived monthly from amateurs in the Variable Star Section of the British Astronomical Association. Harvard’s own professional staff still led the charge, with Leon Campbell alone averaging a thousand observations per month through a 24-inch reflector. Campbell’s attentions shifted in the spring of 1911, when Pickering sent him to Arequipa as director of the Boyden Station. The new post positioned Campbell to keep vigil over the long-neglected long-period variables of the southern sky, but also forced his abandonment of the northern ones. To fill Campbell’s vacancy, Pickering called on the corps of volunteers. He drew up a list of 374 variables requiring frequent surveillance and assigned each star to one or
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j The Brick Building
where the glass plates were stored became a second home to Annie Cannon (left), who classified more than a quarter of a million stars by their spectra, and her colleague Henrietta Leavitt, who sought out variable stars and monitored their behavior.
History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv more regular observers. He also circulated the list as an invitation for others to participate. Given the interruptions to be expected from inclement weather, moonlight, and personal engagements, one star could never have too many pairs of eyes on it. He prepared printed forms to facilitate the filing of reports, provided finder charts to help new recruits locate their stars, and promised to publish the volunteers’ observations. Hoping to head off any needless duplication of effort, Pickering urged his troops to communicate among themselves and cooperate wherever possible, such as by observing at different times of the month and different hours of the night. Popular Astronomy editor Herbert C. Wilson saw the need for an even higher order of organization among variable stargazers. In the August-September 1911 issue of the magazine, Wilson entreated his readers, “Can we not have in America an association of observers with a ‘Variable Star Section,’ a ‘Jupiter Section,’ etc.?” In almost instant reply, lawyer and avid amateur observer William Tyler Olcott of Norwich, Connecticut, announced the October formation of the American Association of Variable Star Observers (AAVSO). Olcott had caught the variable-star fever from Pickering at a public lecture the director gave in 1909. The two corresponded afterward, and Pickering, recognizing Olcott’s dedication, arranged for Leon Campbell to coach him at his Connecticut home. The founding of the AAVSO cemented the already close ties between Olcott and Harvard. Professor Anne Sewell Young of Mount Holyoke, one of Pickering’s most reliable regulars, immediately signed up as a charter member of Olcott’s association. In December 1911 her recent observations formed part of the AAVSO’s first published report in the pages of Popular Astronomy. Soon Sarah Whiting and her assistant Leah Allen of the Wellesley College Observatory joined the AAVSO, as well as Maria Mitchell’s successor at Vassar, Caroline Furness. The group welcomed devotees from any sort of day job. Charles Y. McAteer, for example, worked as a locomotive engineer for the Pittsburgh, Cincinnati,
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j Miss Cannon said
she did not mind climbing up and down ladders to operate the 13-inch Boyden telescope and take her own plates of the southern stars.
History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv Chicago & St. Louis Railway Co. At the end of the night freight run into Pittsburgh, he would go home to the 3-inch telescope in his backyard and observe variables till dawn. When Edward Pickering died in 1919, after a 42-year career as observatory director, his protégée Annie Jump Cannon celebrated him in the pages of Popular Astronomy.
“He will be missed for his warm-heartedness, always eager to help the young astronomer, whether by securing grants of funds or in the selection of his life work; for his cordiality, the ideal host in welcoming visitors to the Observatory; for his sympathetic, inspiring personality, which, by its very optimism and faith in humanity, made us believe in ourselves and our capabilities.” Miss Cannon concluded, “His joy in taking part in what he called the greatest problem ever presented to the mind of man, the study of the starry universe, never left him, and, even in his last illness, he spoke of having new ideas about work . . . He measured the light of the stars and first placed them in an orderly evolutionary sequence. He left, as his legacy to the world, the history of the sky for the last thirty-five years imprinted on the Harvard collection of photographs.” The singular photographic archive that Pickering started in the early 1880s continued to grow for another 60 years after his death. The Brick Building he constructed in 1893 specifically to house them had to be expanded in 1902 and again in 1931.
No astronomer working today uses glass plates to photograph the cosmos.
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j Roughly half a
million glass plates tilt to the left and right on shelves inside metal cabinets at the Harvard Plate Stacks. Each plate’s paper jacket identifies the date the photograph was taken, the celestial area covered, the telescope employed, the duration of exposure, the condition of the sky, and other pertinent information.
History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv CCDs, or charge-coupled devices, began replacing photographic film in the 1970s, and for the past two decades virtually all celestial images have been captured and stored digitally. But no matter how broadly or deeply modern sky surveys probe outer space, they cannot see what the heavens looked like on any given date between 1885 and 1992. The record preserved in the Harvard plate collection of 100 years of starry nights remains unique, invaluable, and irreplaceable. The half a million glass plates reside in the expanded Brick Building. They stand on their long edges, leaning slightly to the left or right on the shelves of the many metal cabinets. Some early photographs still wear their original paper jackets, covered over with hand-written commentary from their long-ago keepers. Old or new, each envelope bears a bar-coded sticker containing accession information that helps the current curator maintain order in the plate stacks. Visiting researchers file in and out. Historians prize the plates for their dated information, for the antiquated union of glass and silver-gelatin emulsion that embeds the stars. Astrophysicists consult the plates to enrich and interpret the latest findings through “time domain astronomy.” Celestial denizens undreamed of at the start of Pickering’s sky patrol—pulsars, quasars, black holes, supernovae, X-ray binaries—nevertheless left their marks on the plates. When computers were human, they scanned these photographs by eye for as many interesting objects as they could find. There were never enough “readers” to utilize the plate library to Pickering’s or Shapley’s satisfaction. The most motivated of their methodical workers, when confronted with an image containing as many as 100,000 stars, could carry discovery only so far. Even now, the information content of the plate stacks is largely untapped. To extract all that waiting data with modern computerized algorithms, the Harvard-Smithsonian Center for Astrophysics inaugurated a digitization project in 2005, with funding from the National Science Foundation. The ongoing goal is to clean, scan, and analyze every plate, so as to provide “Digital Access
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j Portion of Plate
b2312 showing the collection’s first image of the Horsehead Nebula. Taken on February 7, 1888, from Cambridge with the 8-inch Bache Doublet, Voigtlander, reworked by Clark. The exposure was 90 minutes centered on 5h55m33s R.A. and -4d57m06s Declination.
History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv to a Sky Century at Harvard,” or DASCH. After more than 10 years, the work is approximately one-quarter complete. All procedures and instruments for DASCH have had to be invented and assembled on site, from the ingenious machine that cleans the plates with ethanol solution to the high-speed scanner that accommodates the standard 8" x 10" and also the Bruce-sized 14" x 17" plates. At each stage of activity, curatorial concerns vie with scientific requirements. For example, the plate-cleaning process, an essential prelude to producing clear, crisp scans, automatically erases any markings jotted on the glass by iconic figures such as Henrietta Leavitt and Annie Cannon. The compromise solution is to photograph each marked photograph before cleaning it—and each jacket, too—to record all those notations. Certain plates are judged too historic to be tampered with and will be archived indefinitely. One of these holds an image of a star field made while the nature of spiral nebulae still sparked debate. On it, someone circled a tiny swirl of matter too small to see without a magnifying loupe. Next to the inked circle, an inked question arises: Galaxy? The index cards and logbooks that list the telescope, sky coordinates, date, and exposure time of each photograph are also coming online, thanks to an army of willing individuals who spend a few hours every day transcribing them via the Smithsonian Institution’s crowd-sourcing platform. Citizen scientists work in front of their own computer screens from high-resolution photographs of each logbook’s hundred pages, each page crammed with statistics and remarks on as many as 20 plates. At the outset, DASCH team members named reasons beyond data mining as justification for their long-term project. They wanted to make the plates
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j Plate b26816 of
Large Magellanic Cloud taken on December 18, 1900, from Arequipa, Peru, with the 8-inch Bache Doublet, Voigtlander, reworked by Clark. The exposure was 60 minutes centered on 5h09m47s R.A. and -67d22m51s Declination. Annotations made on the back of the plate were not removed because this plate is referenced in the Henrietta Leavitt logbooks made during her research on Cepheid stars.
History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv available for convenient worldwide use, to protect them from careless handling by interested borrowers, and to save the contents from predictable deterioration, such as emulsion separation. Once the process was underway, an unanticipated event provided further justification for the effort. On Monday morning, January 18, 2016, a water main burst under a courtyard at 60 Garden Street, the official address of the CfA. The pipe provided water to four nearby buildings, including the original Brick Building and its 1902 and 1931 extensions. The rupture released water underground with enough force to breach the foundation walls and flood the lower level of the plate vault. Approximately 61,000 plates were submerged. Experts from the on-campus Weissman Preservation Center responded to the emergency and diagnosed mold as the worst-case outcome of immersion. Spores that colonized the plates might configure their own new biological constellations. For all of Pickering’s foresight in initiating and protecting the collection, he never suspected that water, not fire, would threaten its integrity. The conservators prescribed the immediate removal of the plates to a dry place where they could be kept well under zero degrees Centi-
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j top: Portion of Plate mf37250 of Rho Ophiucus taken on
May 30, 1948, from Bloemfontein with the 10-inch Metcalf Triplet. The exposure was 45 minutes centered on 16h26m07s R.A. and -26d19m43s Declination. bottom: Portion of Plate b41215 of Halley’s comet taken on April 21, 1910, from Arequipa, Peru, with the 8-inch Bache Doublet, Voigtlander. The exposure was 30 minutes centered on 23h41m29s R.A. and +07d21m09s Declination.
History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv
j A Series • The 24-inch Bruce Doublet
This telescope was first installed in Cambridge from 1893 to 1895 on the Harvard campus (a). The telescope was then moved to Harvard Boyden Station in Arequipa, Peru, in 1896 (b). Shown here is the Boyden Station in 1897 with the Bruce building in the center and Misti volcano in the background. Image (c) shows the interior of the Bruce building. The telescope was later moved in 1929 to the Boyden Station in Bloemfontein, South Africa (d). Use of the Bruce Doublet at Boyden Observatory was discontinued in 1950. It was replaced by the ADH telescope.
grade—too cold for mold to grow. The prevailing weather conditions at the time, clear with temperatures below freezing, turned the outdoors into a temporary safe haven. As soon as all the water had been pumped out of the building on Monday, dozens of volunteers came to the collection’s aid; they traipsed in and out of the stacks all through Tuesday night and Wednesday, carrying armloads of fragile plates to dry ground. Not a single piece of glass was broken. By Thursday the rescued plates had been driven in trucks to the Polygon Document Restoration
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popularastronomy.com | Fall 2017
a
c
d
b
History of Astronomy | Feature
bvvvvvvvvvvvvvvvvvvvvvvvv Services in North Andover, where they were put into frozen storage, to be later thawed out and cleaned, one by one. One by one, the way the stars emerge as evening falls, the drowned, muddied plates will revive the vivid skyscapes that first impressed them when they were sensitive to light. Once again they will reveal the stellar spectra, the variable stars, the star clusters, the spiral galaxies, and all the other luminous sights they once conveyed to a small but dedicated circle of women. PA •••••••••••••••••••••••••••••••••••••••••••••• Sections highlighted in brown indicate experpts from Dava Sovel’s book The Glass Universe. ••••••••••••••••••••••••••••••••••••••••••••••
About the Author vvvvb
The Glass Universe i
In the 1870s, before women had the right to vote or a firm standing in the workplace, a lucky few found employment at the Harvard College Observatory. The first female assistants were born to the work—as the wives, daughters, and sisters of the resident astronomers. Over time other ladies joined the group, thanks to the director’s farsighted hiring practices and the introduction of photography to astronomy. Instead of observing through the telescope by night, the women could analyze the stars in daylight on glass photographic plates. Harvard’s female workforce grew accordingly, and its individual members won national and international acclaim for their discoveries. The most famous among them—Williamina Fleming, Antonia Maury, Annie Jump Cannon, Henrietta Leavitt, and Cecilia PayneGaposchkin—are the heroines of this story. The work was not only performed by women but also funded by female philanthropists such as Anna Palmer Draper and Catherine Wolfe Bruce. The halfmillion glass plates captured through a century’s worth of observing still occupy their own building at what is today the Harvard-Smithsonian Center for Astrophysics.
Dava Sobel, author of The Glass Universe, has written several national and international best-sellers about the history of astronomy, including Longitude, Galileo’s Daughter, and The Planets. Her stage play based on the life of Copernicus, And the Sun Stood Still, first appeared as the centerpiece of her otherwise nonfiction narrative, A More Perfect Heaven. She has also co-authored six books, such as The Illustrated Longitude with William J. H. Andrewes and Is Anyone Out There? with astronomer Frank Drake. A former science reporter for The New York Times, Sobel has won awards for her writing from the National Science Board, the Boston Museum of Science, the Astronomical Society of the Pacific, and the Worshipful Company of Clockmakers. An asteroid was named in her honor—30935davasobel. Sobel has taught science writing at the University of Chicago, Mary Baldwin College in Staunton, Virginia, and, most recently, Smith College in Northampton, Massachusetts. Learn more about her at www.davasobel.com.
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BUY
Events
Totality! The Solar Eclipse of August 21, 2017 By Jeffrey Bennett
O
n August 21, 2017, we’ll have the first
total solar eclipse to touch the continental United States in almost 40 years. You don’t want to miss it. Let me tell you why.
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This composite image shows the sun’s corona during a total solar eclipse in Svalbard, Norway, in 2015. Credit: Miloslav Druckmüller. Click here for more great photos.
Events | Eclipse 2017
W
hat would you think if the day suddenly began to turn into night, even while the sun was still high in the sky?
It might sound a bit scary, and for most of human history, it was.
Students in Tanzania using eclipse glasses to protect their eyes so that they can observe the partial phases of a solar eclipse. Photo courtesy of Astronomers Without Borders. Learn more about them here.
30
As the sun began to disappear,
Today, eclipses no longer catch
some imagined it as a sign of angry
us by surprise. This means we can
gods, others of celestial monsters
come to them prepared, allowing
consuming the sun. One eclipse sto-
us to watch the partial phases, to
ry concerns two great armies—the
look up in awe during totality, and
Medes and Lydians—who signed a
to marvel at the fact that events
peace treaty before a great battle was
that terrified and mystified our an-
set to begin. According to legend, the
cestors are now so well understood
treaty was the result of a solar eclipse
that we can predict them centuries
that occurred as the armies massed
in advance.
for battle, which so frightened them
To witness the total solar eclipse
that they opted instead for peace. We
of August 21, 2017, you will need to
might hope that upcoming eclipses
be somewhere within the narrow
will have similar effects.
path of totality shown on the map on
popularastronomy.com | Fall 2017
Events | Eclipse 2017
The path of totality for the August 21, 2017, solar eclipse. Orange lines mark the edges of the path, and the blue is the centerline. Other regions on this map will see a partial solar eclipse. Compiled by
this page. Elsewhere in the
As shown in the figure below, the
United States and surrounding
moon’s shadow consists of two re-
countries, you’ll see a partial
gions. Within the full shadow (or
solar eclipse. To understand
umbra), the moon completely blocks
why you don’t want to miss
the sun, creating a total solar eclipse.
this event, we need to first talk
Within the partial shadow (or pen-
Xavier Jubier. Click
about how eclipses occur.
umbra) the moon only partially
here for more interactive maps.
A solar eclipse occurs when
blocks the sun, creating a
the moon passes directly be-
partial solar eclipse. The
tween Earth and the sun, so that the
moon’s orbital motion
moon’s shadow falls on our planet.
around Earth causes the
Partial Shadow (penumbra)
Full Shadow (umbra)
Moon
The moon’s shadow consists of both full and partial regions. Note: The sizes of the moon and Earth are to scale in this diagram, but the distance between them on the same scale is about 50 times that shown here; the sun, in turn, should be about 100 times the size shown here and 400 times as far from Earth as the moon. Art courtesy of Big Kid Science. Click
Sun
Earth
here to learn more eclipses.
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popularastronomy.com | Fall 2017
Events | Eclipse 2017
Path of Totality August 21, 2017
This map shows the paths of totality both for August 21, 2017, and for April 8, 2024. Based on Xavier
Path of Totality April 8, 2024
Jubier’s interactive eclipsemapping tool. Click here for more past and future paths.
shadows to race across our planet’s
solar eclipses at any particular lo-
surface at typical speeds above
cation is about 375 years. However,
1,000 miles per hour and generally
there is great variation. For exam-
from west to east. That is why the
ple, a small region just south of St.
full shadow traces a narrow path,
Louis, Missouri, will have a second
and why totality lasts only minutes
solar eclipse less than seven years
(or less) in any particular place.
after the August 21 eclipse. In con-
On average, a total solar eclipse
trast, Los Angeles last had a total so-
happens somewhere on Earth about
lar eclipse on May 22, 1724, and will
every year and a half, but the nar-
not have another until April 1, 3290.
rowness of the path of totality means
With that, let’s turn our atten-
that the average time between total
tion to safely observing the August
The diamond ring effect occurs just before the onset of totality (and again as totality ends). The last bit of bright sunlight from the sun’s surface makes the “diamond,” and the sun’s outer atmosphere, or corona, makes the ring around the edges of the moon. Credit: Rick Fienberg /TravelQuest International/ Wilderness Travel
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21 eclipse. You know better than to stare at the sun on normal days, and eclipse days are no different. You must never look directly at the sun as long as even a tiny portion of it remains unblocked by the moon. This means you have two basic options for viewing the partial phases of a solar eclipse. First, you can use projection, which can be as simple as poking a small hole in a sheet of cardstock and hold-
Events | Eclipse 2017
ing it so sunlight forms a small image behind it. (In fact, almost any small opening will act as a pinhole projector, which is why you may see multiple projections of the partially eclipsed sun in the shadow of a tree, each created as sunlight passes through a small gap among the leaves.) You can create larger images by projecting sunlight through binoculars or a telescope set up backwards; just be careful, because the concentrated sunlight can be very hot. (Alternatively, you can purchase special solar filters that can allow you to look through cameras, binoculars, or telescopes safely.) The second option, which is generally also more fun, is to use special eclipse glasses. These are safe and inexpensive (typically $1 to $2 per
Using projection to view a partial solar eclipse will work well, whether you are using equipment or viewing with the naked eye. Art courtesy of Big Kid Science.
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pair), but be sure you purchase them from a reputable source and that the
Credit: Miloslav DruckmĂźller.
Events | Eclipse 2017
lenses are not scratched or damaged. You can try our Totality app eclipse glasses, which you can order via the link at
BUY
www.bigkidscience.com/eclipse/shop/. Just remember that you should never look toward the sun without these glasses, with one exception: if you are lucky enough to be on the path of totality, you can and should remove the glasses during your brief minutes of totality. This brings me to why I hope you’ll try to be on the path of totality. If you explore an interactive map of the eclipse, such as the one you’ll find within the
GET
free Totality app, you’ll notice that most places in the continental United States will have a substantial partial eclipse. This might make you think that you can stay home and “almost” see a total solar eclipse, but the difference between even a 99% partial solar eclipse and a total solar eclipse is literally the difference between day and night! The reason is simple: the sun is so bright that even a 99% partial solar eclipse will still allow enough light through to keep the sky daylit and to keep it unsafe to
34
popularastronomy.com | Fall 2017
For a few brief moments, a total solar eclipse turns day into night, as shown in this photo taken over Château de Courcelles in France. (The radiating lines are camera artifacts.)
Events | Eclipse 2017
look at the sun without eclipse
appear behind the moon, you will
glasses.
see the spectacular diamond ring
In contrast, under clear skies on
effect, which tells you it is safe to
the path of totality, you’ll get an
remove your eclipse glasses. With
experience you’ll never forget. The
the sun’s visible disc completely
partial phase will begin a little over
blocked by the moon, you’ll be able
an hour before the big moment. You
to see the sun’s outer atmosphere,
won’t notice much at first, but as the
or corona, which is otherwise far
partial phase progresses, the light
too faint to see. The coronal light
around you will begin to dim, and the
will give the sky a twilight glow, but
temperature will begin to drop. Ani-
it will still become dark enough for
mals may behave strangely, with bird
you to see planets and bright stars.
songs going silent, while nocturnal
The only thing that can dampen
owls and bats awaken. As totality ap-
the experience is clouds, but even
proaches, in the distance you may
then, you may be lucky enough for
see the moon’s full shadow coming
the eclipsed sun to peek through.
toward you across the landscape.
The photo on page 34 comes from
When the last rays of sunlight dis-
GET
an eclipse I saw in 1999. It was so
To learn more, including the how much of an eclipse you can see at any location, the exact local times of the eclipse, and how and why eclipses occur, be sure to download the free app Totality by Big Kid Science, available both for iOS and Android. Please note that Totality is brought to you as a public service by Big Kid Science. If you like the app, please be sure to rate it, and you can also show your support by purchasing books or donating to our favorite nonprofits through the “Shop” screen within the app.
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popularastronomy.com | Fall 2017
Events | Eclipse 2017
cloudy that we saw virtually noth-
eclipse glasses or other safe viewing
ing of the partial phases, but just as
devices. Moreover, for this year’s
totality began, the clouds opened up
eclipse, the amount of totality along
to give us this spectacular view.
the centerline varies only slight-
I hope I’ve convinced you that
ly, and weather prospects are good
totality is worth seeing, especial-
in most places, so you can be very
ly since it should be within about
flexible in choosing where to watch
a day’s drive for almost everyone
totality. (Use the Totality app to find
in the United States. So at the risk
more information about choosing a
of upsetting school administrators
site: on the main menu, tap “Learn”
and employers, I urge you to make
and then tap “Eclipse 2017.”)
August 21, 2017, a personal holiday.
If you simply can’t get to totali-
Because this is a Monday, you can
ty, I hope you’ll still watch the par-
make it a three-day weekend, giv-
tial eclipse, and urge every school
ing you plenty of time to find your
in the country to host an eclipse-
way to the path of totality. Just be
watching event for students and
sure to look for lodging or campsites
families. Again, this requires nothing
soon, as they are filling fast. And I’d
more than an unobstructed view of
urge you to avoid planning to drive
the sun and your eclipse glasses, so
on eclipse day, as traffic is likely to
you can host events at playgrounds,
be very heavy as millions of people
school yards, or even stadiums.
head toward a view of totality.
For most people, a total so-
In terms of logistics, viewing a
lar eclipse is a once-in-a-lifetime
total solar eclipse is very easy. Be-
event that will inspire awe of nature,
cause it is a daytime event, the only
humility in our place in the cosmos,
thing you need to see it is an unob-
and, hopefully, a lifelong interest in
structed view of the sun and your
science. Please don’t miss out.
About the Author Jeffrey Bennett, the founder of Big Kid Science, is an astrophysicist and an award-winning author of children’s books, general science books, and college textbooks. His personal website is www.JeffreyBennett.com. On eclipse day, he will be hosting events in Idaho Falls, ID.
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popularastronomy.com | Fall 2017
PA
To learn more about the upcoming eclipse, please also visit TechnicaCuriosa.com, where our special guest is award-winning science educator, Andrew Fraknoi.
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Exoplanets
I
became hooked on planets when I was six years old. I was extremely fortunate to grow up in western Kentucky, far from city lights, where the night skies were so dark you could truly see thousands of stars and the Milky Way was a bright, jag-
ged band of light across the sky. I was endlessly fascinated with the stars and the moon. I knew from the few books that I had that there were planets out there as well, but because they appeared as just specks of light like the rest of the stars I wasn’t able to identify them. In hindsight, being in a location where I could see the stars and the Milky Way so clearly was perhaps one of the key things that motivated me to become a scientist. I was the sort of kid that asked so many questions that could drive adults a bit crazy. I would follow every answer with another question: Why? I think that was the reason that my father decided to get me a small telescope, hoping that it would answer my questions about the sky. But it didn’t quite work the way he hoped.
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popularastronomy.com | Fall 2017
Exoplanets | Planetary Zoo
Studying the sky with a telescope just opened up more questions in my mind. But he was patient and encouraged me as much as he could with books and tools to build bigger telescopes. Although I was thrilled when I got that first telescope, I really had no idea how it worked or what to do with it. The first night, I set it up in our back yard on its rickety stand, and I simply pointed it at the brightest star I could see. Amazingly, and it still astonishes me to this very day, that “star” turned out to be the planet Saturn. In my small telescope I could clearly see the tiny image of a roundish object with “bulges” on its sides. I’d seen Saturn in picture books, and I knew this had to be it. In my mind’s eye I can still clearly see that tiny image. I can also remember being so totally speechless at my first look through the telescope that I couldn’t even explain it to my parents. I made them come outside to look through the telescope for themselves! Seeing Saturn first-hand encouraged me to learn as much as I could about it over the years. It is still difficult for me to imagine an object 90 times the mass of the Earth. If we put Saturn midway between the Earth and the moon, its outer rings would encompass both! For anyone who followed the Apollo missions to the moon this should be a completely mind-blowing concept. Looking at the moon in my telescope was continually fascinating. I studied every detail on its surface. By the time I was 10 years old I knew my way around the surface of the moon better than my hometown. With my telescope I
39
popularastronomy.com | Fall 2017
Saturn’s moon Titan seen in front of Saturn and near the ring plane. The shadows of Saturn’s rings are seen across the planet’s disc. Image taken from the NASA Cassini spacecraft.
Exoplanets | Planetary Zoo
Another image from the NASA Cassini spacecraft. Saturn observed from the side opposite that of the sun. Sunlight forward scattered through Saturn’s outer thin ring particles makes them appear bright. Planetary rings, due to disruption of nearby moons, are likely common among large planets in the galaxy.
was able to see the four large Galilean moons of Jupiter and watched them change position every night. Almost any time the night skies were clear I was outside looking up into the sky. There was no question about it after that—I was hooked on astronomy, and especially planets. I read all I could about planets. As a teenager I built bigger and bigger telescopes, then went to college and used their much larger campus telescope to study Saturn, Jupiter, and other objects. Seventeen years after getting my first telescope I was in graduate school at Caltech beginning my Ph.D. thesis studying the atmosphere of Jupiter’s volcanically active moon Io. There I was able to use the largest telescope in the world at the time, the Palomar 5-meter telescope, to study Io’s atmosphere escaping into Jupiter’s magnetosphere. By that time NASA had two spacecraft, Voyager 1 and 2, making the first detailed robotic reconnaissance of the giant planets. In addition to sending back incredible images of Jupiter and Saturn, those spacecraft revealed a diverse set of moons around both—revealing them as miniature “planetary systems” in their own right. Jupiter’s four moons included three—Europa, Ganymede, and Callisto—each of which we learned has a subsurface liquid water ocean with more water than in all the oceans on Earth combined. And they could be habitable! Saturn has a large moon Titan that has a nitrogen atmosphere with rich organic chemistry and seas of hydrocarbons sprinkled about on its surface. We now know that Enceladus, a much smaller moon of Saturn, also has a subsurface water ocean spewing hot water into space with a mixture of salt, methane, carbon dioxide, and molecular hydrogen—all the essential ingredients we know that are required for life as we know it. By the time I finished my Ph.D. thesis in 1985,
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Exoplanets | Planetary Zoo
NASA and the planetary science community had finished its initial reconnaissance of the two major “types” of planets in our solar system that we knew of at the time: the terrestrial planets like the Earth, Mars, Venus, and Mercury, and the giant planets like Jupiter, Saturn, Uranus, and Neptune. Each type is clearly distinct, with the terrestrial planets being smaller and composed of heavy metals and rocky materials, whereas the giant planets are composed of lighter constituents, such as hydrogen, helium, and methane. There are many other differences as well, but these are the two distinct categories we understood by the end of the 1980s. Pluto as observed from the NASA New Horizons flyby in July 2015. Close-up of Pluto’s Sputnik Planum region, which is a solid nitrogen glacier filling a massive depression that was created by a large asteroid impact. The water ice crust of Pluto is thought to lie over an ocean of liquid water.
The ninth planet, Pluto, didn’t fit into either of these categories. With the discovery of the first Kuiper Belt Objects in 1992 it became clear that our solar system has a third type of planet, called dwarf planets, that orbited mainly beyond the orbit of Neptune at distances about 30 to 50 times the average sun-Earth distance (a unit we call the astronomical unit, or AU). Estimates have placed the number of these dwarf planets in the tens of thousands, perhaps as many as 100,000. Pluto is one of the larger Kuiper Belt Objects. But it wasn’t until the New Horizons spacecraft, launched in 2006 and which provided us with a flyby of Pluto in 2015, that we got our first close-up view of this third category of planet. We were all amazed to find that Pluto was a world far more active, complex, and mysterious than anyone ever imagined. Pluto is a world of ice and rock, with a diverse surface geology driven by an as-yetunknown energy source, evidence of
41
popularastronomy.com | Fall 2017
Exoplanets | Planetary Zoo
major long-term climatic variations—frozen lakes, a surface covered by complex organic compounds, and an atmosphere with layered structures that still defy a satisfying explanation. Pluto has five moons, and there is strong evidence that Pluto has a subsurface ocean of liquid water as well. So even though we have a close-up view of only one High-resolution image of Pluto’s limb from the New Horizons flyby showing bright atmospheric haze from scattered sunlight. The haze has numerous thin embedded layers of thicknesses of only a few kilometers that are unlike anything else seen in our solar system. Pluto, along with Saturn’s moons Enceladus and Titan and Jupiter’s moons Europa, Ganymede, and Callisto, may be examples of ice-covered water worlds that are common in the galaxy.
42
of the vast number of Kuiper Belt Objects, the diversity seen on both Pluto’s surface and in the colors and reflectivities of other small planets in the Kuiper Belt suggests that the Kuiper Belt is a vast arena of complex types of planetary behaviors. And while the New Horizons spacecraft was on its way to the third category of planets in our solar system, evidence was building that other solar systems were not just common but perhaps equally complex, and they were appearing more and more bizarre as we began discovering them. The first definitive discovery of planets outside of our solar system came from the study of pulsars, the remnants of supernova explosions. Detailed study of high-energy emissions from two of these rapidly rotating objects revealed orbiting planets. Supernova explosions are some of the most energetic events known, representing the conversion of a large fraction of a star’s rest mass into energy. A single supernova explosion can generate as much radiant energy as our entire galaxy for a short period of time. Such an energetic explosion should disintegrate orbiting planets. Yet there they were! Planets were much hardier than we thought, or perhaps they were able to reform
popularastronomy.com | Fall 2017
Exoplanets | Planetary Zoo
Close-up of Jupiter as seen from the NASA Juno spacecraft. Jupiter’s atmosphere is seen to be highly turbulent with storms larger than the Earth. Every planet in the galaxy is unique and has its own unique meteorology.
after such explosions. We now had a new fourth category of planets to add to the three we were so familiar with in our solar system. A few years after the discovery of pulsar planets, a new method, call the radial velocity technique, was developed which could measure gravitational tugs on stars due to orbiting planets. Soon hundreds of additional planets were discovered—mostly large planets like the giants in our solar system but in orbits much closer to their central star. Many of these orbit with periods as short as a few Earth days and are so close that they are within the hot corona of their central star. Try to imagine the aurora produced by their central star’s hot coronal wind, which may have a temperature in the millions of degrees Kelvin and is moving at velocities of thousands of kilometers per second, hitting the magnetic field of these hot Jupiters and being funneled into their polar regions. The aurora on these planets would be millions of times brighter than anything we’ve ever seen on Earth. Truly an exotic fifth category of planets to add to our rapidly expanding list! With the launch of the Kepler Space Telescope in 2009 yet another highly sensitive technique was uti-
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Exoplanets | Planetary Zoo
lized to detect planets around distant stars. The transit technique was able to measure the dimming of a star’s light as an orbiting planet moves in front of the star. This technique allowed the detection of much smaller planets with longer periods and hence more distant orbits, as well as to characterize their size, mass, and, in some cases, their atmospheric compositions and temperatures. With the successes of these techniques, soon we had thousands of new planets to study. One fascinating example is the small, terrestrial-like (mostly metal and rock) planets in close orbits to their central star that we now call hot Earths. Many of these are tidally locked to their central star, having the same side always facing their star, much like our moon does to the Earth. Although these are Earth-sized, they have dayside surfaces covered with magma and atmospheres of vaporized rocks and metals. Their atmospheres would flow supersonically around to the night side where it freezes out and perhaps snows rock “snowflakes.” I wonder if those snowflakes have a preferred symmetry such as the hexagonal symmetry of water ice snowflakes on Earth. Perhaps each rock snowflake is just as unique as ice snowflakes here on Earth. If you’re still counting, that is planet category number six.
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There may be many times more rogue planets in the galaxy than the number of planets gravitationally bound to stars. Rogue planets retain their heat of formation for billions of years, and so their interiors might remain habitable for life as we know it.
Exoplanets | Planetary Zoo
We also found planets that were terrestrial—made of rocks and metals—yet several times more massive than the Earth. These super Earths almost certainly have thicker atmospheres than we have on Earth, partly due to the higher gravity. Many of these super Earths might end up in runaway greenhouse situations like Venus with a hellishly hot surface and an atmosphere 100 times the sea-level pressure on Earth. They might also recycle that atmosphere if they have rapid plate tectonics like Earth, and might even be habitable. This makes category number seven! Even more amazing was that some of these super Earths have densities much less than that expected for rocky/metallic planets like that of the Earth. Their densities match much better with that of water, such as GJ 1214b. Water worlds became our eighth category. Water worlds are unlikely to be made entirely of water. They probably have cores of metals and rocks like the terrestrial planets but with mantles of water perhaps thousands of kilometers thick. They might have a rain of asteroidal and cometary debris that burns up in their atmospheres and falls through the oceans. It’s fun to speculate on the internal structure of such water worlds. As one moves inward from the surface to the center of a water world, you would probably encounter a layered structure, somewhat like an onion, with sharp density gradients occurring where the increasing pressure on the water produces phases that we rarely encounter on Earth—and then only in Water worlds might have oceans 10,000 kilometers thick and complex internal oceanic “meteorologies” that move around heavier elements and energy. Extreme forms of barophiles that exist on Earth—organisms that live in the deep ocean—might inhabit their deep waters.
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Exoplanets | Planetary Zoo
specialized laboratory experiments. Each layer might have its own distinctive oceanic “meteorology.” The surfaces could range from ice, such as that which covers the surface of Europa’s ocean, if the planet is far from its central star, to steam atmospheres with an extreme greenhouse effect if the planet is close to its central star. At the other extreme in planetary density are some of the extrasolar planets discovered by the Kepler Space Telescope that appear to have overall mass densities corresponding to mostly metal. These metallic planets are planet category nine. The planet Mercury in our own solar system might fit nicely in this category. These might be hot and molten on their surfaces if they are close to their central star, or they could be so cold that the surface could be near superconducting temperatures if distant from their star. A superconducting planet might have unbelievably complex electric and magnetic fields, which could become more complex over time as those fields that are more robust dominate over those less so. Could that be an electromagnetic type of Darwinian evolution? Could electromagnetic intelligence evolve on such a world? Of particular fascination are the so-called diamond worlds, which have an overall density that is consistent with that of the element carbon. One of these, Cancri 55e, is six to seven times as massive as the Earth and orbits its central star in about 18 Earth hours! If it is mostly carbon, then it could have a mantle 10,000 km thick of some form of crystalline carbon. The estimated pressure at the center of such a planet is on the order of 100 million times sea-level pressure. Would crystalline carbon become a semisolid at such pressures and flow as a liquid? Although the diamond worlds are probably much more complex in composition and structure than this simple picture, they would indeed be interesting places to explore to see what kind of complex carbon structures nature might create— perhaps carbon topologies much more complex than what we find in biological systems on Earth. Perhaps the carbon structures there
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become self-replicating as well. There is certainly plenty of energy available to drive such evolution. Category 10! There are also low-density planets that appear to have a density lower than that expected for a hydrogen and helium composition. Are these rapid rotators where the outward centrifugal force is countering gravity so as to make them larger than they would be otherwise? Or do they have very extended atmospheres? This is category 11. They might be in a transient stage just before they become unstable and disintegrate. The next few categories show us worlds even more bizarre and difficult to imagine. There is evidence that the interstellar medium is populated with “rogue worlds” not gravitationally bound to stars at all. We don’t know how many are out there, but suggestions are that the number is truly vast. To get some insight as to how these rogue worlds might form, consider just the example of what we’ve inferred about the history of our solar system. There is evidence of at least four planetary collisions, or near collisions, that occurred in the early years of our solar system. These include the collision that formed our moon, the collision that stripped away Mercury’s crust, the collision that “tilted” Uranus, and the collision which formed the Pluto-Charon double planet. There may have also been a near collision that created the Tharsis Bulge on Mars, and another that reversed the spin of Venus on its axis. There is also indirect evidence of a massive outer giant planet “rearrangement” early in the history our solar system. That rearrangement may have triggered the inward flux of comets and asteroids that bombarded the Earth, bringing with them the water in our oceans. Each of these events may have led to either planetary disintegrations or ejection of a planet from the solar system. There were probably many more such near-collisions for which we have no evidence.
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There is a general sense that the formation of planetary systems and the subsequent gravitational collisions described above lead to the ejection of a comparable number of rogue planets as those which stay gravitationally bound to the central star. If so, there could be many more rogue planets than stars. Extrapolations of the statistics based upon the still few detections of rogue worlds by gravitational lensing (when they move in front of background stars and briefly focus that star’s light) suggest that enormous numbers of rogue worlds are actually out there. If such large numbers of these dark rogue worlds (category 12) exist, then the interstellar medium is vastly different than has been generally assumed. For example, this could drastically change our notions of interstellar travel. Instead of interstellar hops of several light years at a time needed to migrate to nearby stars, which would require generation starships, we could travel perhaps shorter trips of a few thousand AUs at a time between rogue worlds. We could stop off at a rogue world, refuel, and get whatever resources needed. Maybe we could set up a human colony there with artificial fusion stars to keep the surfaces warm. Then we could move on to the next rogue world. Colonizing the galaxy would still be a diffusion process but with much smaller steps. The problem, of course, is detecting the rogue worlds. They are much too distant from stars to be seen by reflected starlight. Most likely we would need to detect them in infrared emission. Our starships would need extremely large, perhaps collapsible, infrared telescopes to find a rogue planet for our next rest stop. Maybe robots could build huge infrared telescopes at each stop in order to find the next rogue planet along our route. The robots could disassemble the telescope and use the materials for something else until such a telescope
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is needed again. Many such approaches can be imagined. The point is that a trip to the nearest known extrasolar planet, Proxima Centauri b, which is about four light years distant, could be accomplished by a dozen or more shorter voyages, each of perhaps 30 to 50 years, and we could colonize the near-by rogue worlds as we go. But it would be a mistake to consider the interstellar rogue worlds dead. First of all, planets like the Earth and even Pluto take billions of years to cool away the interior energy remaining from their formation. For a planet as large as Jupiter, it could take tens of billions of years to cool. A water world of several Earth masses that is ejected from a planetary system might stay liquid at depth for many tens of billions of years. Life inside that water world might continue largely unaffected for billions of years. Consider what would happen to a system like Jupiter and its four large moons if they were ejected into interstellar space as a group. They would become extremely dim in reflected visible light—actually almost invisible. But Jupiter emits much more energy in the infrared than it receives from the sun. The four moons are all heated by tidal interactions between Jupiter and each other, so Io would stay volcanically active and the subsurface oceans on Europa, Ganymede, and Callisto would remain liquid for as long as the tidal interactions continued. Any lifeforms that evolved inside these moons, or inside Jupiter itself for that matter, would continue having the same energy sources for many billions of years. Actually, things would go on mostly the same for such a system, but in interstellar space, far from stars. We could easily continue describing tentative new categories of planets that have been discovered, or others that we strongly suspect will be discovered in the near future. For example, we’ve found planets that orbit multiple star systems (this would be category 13); one example was in a four-star system. We’ve found Earth-sized planets with steam atmospheres
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(GJ-1132b—it contains methane as well!). We’ve found terrestrial planets around M-dwarf stars (e.g., the TRAPPIST-1 system with seven Earth-sized planets, three of which are in that star’s habitable zone), perhaps the most common type of star in our galaxy. There may be hundreds of categories of planets out there waiting to be discovered. Viewing planets in all their diverse forms is like walking through an incredibly immense zoo of planetary types, and here we’ve just passed by the first few exhibits in that zoo. But by what we’ve discovered so far we can already see that planets appear in a vast variety of sizes, masses, compositions, degrees of habitability, and even locations. At this point we can merely guess at the various zoo exhibits of planet types that we will discover in the near future. But most likely our guesses will be wrong. The universe always seems to have a way of being more creative than we are. The new science of planetary taxonomy will have much work to do, and clearly those who are its practitioners will have a challenging future. Once butterflies were classified in the old science of taxonomy according to their wing colors, shapes, sizes, etc. After we developed the technology to map their genetic code, we were able to characterize their intrinsic nature, which then led to a much greater insight into their evolutionary heritage and into their lives, and thus how they were related. We have learned that life is part of a continuum from biomolecules to amino acids, proteins and enzymes, autocatalytic systems, viruses, cells, multicellular organisms, intelligence, civilization, and so forth. Organisms on Earth are born, they develop according to their genetic programming and their environment, evolve according to the events they experience, and they die. In a general sense planets are somewhat like life. Planets are born as a byproduct of star formation. Planets are made of elements, minerals, complex molecules, cores, mantles, crusts, atmospheres, and oceans, all of which depend upon the initial characteristics of the molecular cloud from which the star and planets form. Planets evolve geologically in a manner determined by these initial characteristics, the laws of physics and chemistry, and as a result of the historical events they experience. And occasionally
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planets die when geology and other internal processes cease or perhaps when an external catastrophe destroys them. The process of categorizing planets is similar to what one encounters when trying to categorize life. In biology, it is surprisingly difficult to define life in a way that is both concise and that encompasses all of its diversity we’ve encountered on Earth. Perhaps we should heed that lesson in our attempts to develop a definition of what constitutes a planet. The rate of discovery of new types of planets should also encourage us to be humble in our approach to such a definition. A general yet minimalistic approach for a working definition of what constitutes a planet is wise until we know much more about what is out there. In planetary science we know that objects tend to become round when their self-gravity is balanced by internal pressure; otherwise, you have an irregular mass known as an asteroid. But if the self-gravity becomes too large then nuclear fusion can be initiated and you then have a star. That is certainly oversimplified, but perhaps we know too little at this point to try to develop a more sophisticated definition of a planet than that it must exist within these bounds. Whatever ultimate planetary classification scheme is developed that adequately characterizes the diversity of planets, that scheme must include the objects in our solar system as well as the vast numbers of planets we’ve discovered elsewhere. Planets need to be characterized based upon their intrinsic nature and environment, not only on where they reside. For example, Triton was once a planet much like Pluto and in its own orbit around the sun before Neptune captured it. Now it is a moon as well as a planet! Often we hear the claim that the discovery of life beyond Earth will represent the ultimate “Copernican Revolution.” When that happens the Earth and its life will no longer be considered as having a truly “special” place in the universe. But the discoveries we are witnessing right now in the vast array of planets beyond our solar system may be the beginning of that final Copernican Revolution. We have been so surprised by the diversity of exoplanets that there is every reason to expect to be just as
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surprised at the various types of life we find elsewhere. Every planet and every form of life will be unique and special. Such surprises are an exciting part of science. And we can expect many more surprises with the rapid pace of exoplanet discovery. And it may be that what we consider life is only one of a near-infinite number of possible types of emergent complexity in the universe. Some types of emergent complexity that we will find he past few years
T
out there might not meet many, or any, of the
have seen an incre-
generally agreed upon characteristics of life on
dible explosion in our
Earth, such as being based upon carbon; needing
knowledge of the uni-
liquid water; exhibiting reproduction, evolution,
verse. Since its 2009
and movement; etc. Yet those entities might be
launch, the Kepler satellite has disco-
BUY
vered more than 2,000
vastly more self-aware and sentient than we are. So looking for life as we know it may be the wrong approach. But the one lesson we have learned in our ex-
exoplanets, or planets outside our solar system.
ploration of the universe is the very same lesson
More exoplanets are being discovered all the time,
I learned when I first looked through a telescope.
and even more remarkable than the sheer number of
Every time we look beyond our ken we are aston-
exoplanets is their variety. In Exoplanets, astronomer
ished at what we see.
Michael Summers and physicist James Trefil explore
PA
these remarkable recent discoveries: planets revolving
About the Author
around pulsars, planets made of diamond, planets that
Michael Summers is a planetary scientist at George Mason University
are mostly water, and numerous rogue planets wan-
in Virginia and a co-investigator on NASA’s New Horizons mission to
dering through the emptiness of space. This captivating
Pluto. He specializes in the study of structure and evolution of plane-
book reveals the latest discoveries and argues that
tary atmospheres. His planetary research has dealt with the chemistry
the incredible richness and complexity we are finding
and thermal structure of the atmospheres of Io (one of the Galilean
necessitates a change in our questions and mental par-
moons of Jupiter), Titan (largest of Saturn’s moons), Uranus, Neptune,
adigms. In short, we have to change how we think about
Triton (largest moon of Neptune), Pluto, and Mars. Dr. Summers’
the universe and our place in it, because it is stranger and more interesting than we could have imagined.
research on the Earth’s atmosphere has focused on understanding middle atmospheric ozone chemistry, coupled chemical-dynamical-radiative modeling of active trace gases, heterogeneous chemistry
on meteor dust, the influence of solar variability on the state of the stratosphere and mesosphere, and polar mesospheric clouds and their connection to climate.
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History of Astronomy
T
o the ancient Greeks, Urania was the muse of the heavens and Uranus was the god of the celestial realm.
The planet Uranus, which was discovered in 1781 by the English astronomer William Herschel, was named after him. Both names, Urania and Uranus, come from the Greek root for sky, urano. The word uranography is derived from that same word and refers to celestial cartography, just as geography refers to terrestrial mapping.
By Wil Tirion
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History of Astronomy | Uranography
The Oldest Star Maps Beyond a doubt, the bright night sky has always made a great impression, and the ancient peoples let their fantasies run wild: In the star patterns they recognized bears, dogs, and hunters. These star groupings became known as constellations, and many of these old constellations are still known today, e.g., the Great Bear, the Lion, the Charioteer, the Scorpion, and the Herdsman.
the stars and especially the planets. Today, if you want to insult an astronomer, you call them an astrologer. Astrology is regarded as a pseudoscience. The 12 constellations of the zodiac that we know from the astrology columns in papers and magazines date from the time of Babylon. Later, in Classical Greek times, many of the old constellations received new names derived from the many gods and semigods in Greek mythology. Orion, Cassiopeia, Cepheus, Andromeda, and Hercules, just to name a few, have survived the centuries and can still be found on modern star charts. One of the earliest uranograph-
The oldest attempts to map the
55
ical works that has been saved is
sky date from the second mille-
the Almagest of the second centu-
nium, before Christ. On boundary
ry A.D. by the Greek astronomer
stones found in the ruins of the
Claudius Ptolemaeus (Ptolemy).
ancient city of Babylon, drawings
The work contained a list of 48
of some of these classical con-
constellations that were recog-
stallations were found. In those
nized in his time and in his part
days, and long after, astronomy
of the world. These 48 constella-
and astrology were connected
tions are still recognized today,
and regarded as the same science.
with just two exceptions. The
The most important task of an
name Serpentarius (serpent bear-
astrologer was to predict the fu-
er) has been changed to the per-
ture by looking at the positions of
sonal name Ophiuchus, and the
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History of Astronomy | Uranography
name Argo (or Argo Navis) does
stars are completely absent (see
not exist anymore, because the
figure 1).
large constellation, the ship Argo,
In Ptolemy’s catalog, stars were
is now divided into three parts:
divided into six classes of bright-
the Stern (Puppis), the Keel (Ca-
ness, or magnitudes. The bright-
rina), and the Sails (Vela).
est stars were called first magni-
The Almagest also contains a
tude, the less bright stars second
list of 1,022 stars measured with
magnitude, and so on. The faint-
an exceptional accuracy for those
est stars, still visible to the naked
days. The positions are given
eye, were called magnitude six.
in ecliptic coordinates, because
This rather rough magnitude
the ecliptic was, due to the im-
scale was refined later on a sci-
portance of astrology, the most
entific (logarithmic) scale by
important line in the sky. But the
the English astronomer Norman
star positions were also given
Pogson. He defined that a star
in a quite different way. In the listing of stars in the Great Bear, you read things like “the star at the tip of the muzzle,” “the western star of those in the two eyes,” or “the western star of the two in the forehead.” This meant that people using that list needed to be familar with the anatomy of those heavenly figures. On many medieval maps the stars seem to be less important than the figures; the correct positioning of the stars was not the first priority. Moreover, on some of these old maps the
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Figure 1. Star map by Giovanni Cinico (Napels, 1469). Notice that there are no stars shown, only the constellation figures.
History of Astronomy | Uranography
of magnitude 1 was exactly 100
Obviously, the scale can be
times as bright as a star of mag-
extended in both directions. Our
nitude 6. This means that a dif-
sun, by far the brightest object
ference of 1 magnitude represents
in the sky, has a magnitude of
a difference in brightness of
-26.74. On the other end of the
2.5119 (the 5th power root of 100).
scale we see that the faintest
Based on this logarithmic scale
stars to be captured on photo-
the brightness of stars is now
graphs by the big ground-based
given with more accuracy, with
telescopes are of approximately
one or two decimals. For instance,
magnitude 27. The Hubble Space
Regulus is a star of magnitude
Telescope has even captured
1.39. On this new scale some stars
stars of magnitude 31 on long
turned out to be brighter than
exposed images.
magnitude 1 and the scale was expanded to 0, but some stars were
New Constellations
even brighter than that. These
In 1515 Albrecht Dürer published
stars have a negative magnitude:
the first printed maps, a pair
Arcturus (-0.05), Rigil Kentau-
of woodcut maps showing the
rus (-0.27), Canopus (-0.74), and
northern and southern hemi-
Sirius (-1.46).
spheres (figure 2). The maps
Figure 2. Northern and southern hemispheres on a pair of woodcut maps from Albrecht Dürer (Neurenberg, 1515).
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Amsterdam, Petrus Plancius. A star list, along with 12 new constellations, was created. Some believe that Keyser and de Houtman invented the constellations, but others say that Petrus Plancius was the spiritual father. Petrus Plancius was a bird lover and among those new constellations we find five birds: the phoenix, the crane, the toucan, the peacock, and the bird of paradise (figure 3). Later, in 1752, the French astronomer Nicolas Louis de Lacaille made more additions to the southern sky by creating a number of “modern” Figure 3. New constellations in the southern sky, pictured on a map by James Barlow (London, 1790).
constellations. So today we have Telescope, Microscope, Octant, Pendulum Clock, and Airpump,
show the 48 classical constellations, listed by Claudius Ptol-
58
alongside the classical figures. The period between 1600 and
emaeus (Ptolemy) in the sec-
1800 was a turbulant time for the
ond century. A large area of the
starry sky. Constellations came
southern sky is still void of con-
and went. Almost everyone who
stellations. In the western world
created star maps invented new
this part of the sky was yet un-
constellations, sometimes to fill
explored. Between 1595 and 1597,
empty spaces, but more fre-
two Dutchmen, Pieter Keyser
quently parts of existing constel-
and Frederick de Houtman ob-
lations were simply amputated to
served the southern sky on their
make room for their own inven-
first expedition to the Far East,
tions. Very often this was done
commissioned by a scientist from
for political reasons, or in other
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History of Astronomy | Uranography
Figure 4. “The Scepter and the Hand of Justice” on a map by Augustin Royer (Paris, 1679). The constellation was dedicated to Emperor Louis XIV.
59
words, to get in good graces with
Some Major Star Atlases
prominent people, like kings and
In 1603 Johann Bayer, a lawyer
emperors. A nice example is The
from Augsburg in Germany, pub-
Scepter and the Hand of Justice
lished a milestone in stellar car-
on a map from 1679 by Augus-
tography, his Uranometria. Bay-
tin Royer, an architect at the
er’s atlas contains 48 star maps,
French Court. It was dedicated
each showing one of the 48
to Emperor Louis XIV of France.
classical constellations from Pto-
It is in the area where we now
lemy’s list, plus one map show-
find Lacerta the Lizard (figure
ing the 12 newly created southern
4). Clearly, these newly invent-
constellations. Bayer was the first
ed constellations usually did not
to use Greek letters to identify
have a long life.
the stars in a constellation. Since
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the publication of Bayer’s Uranometria, Betelgeuse in the constellation of Orion is also known as α (Alpha) Orionis and Rigel as β (Beta) Orionis. It is a general misconception that he always assigned the first letter of the Greek alphabet (α) to the brightest star. There are many obvious examples where Bayer probably used different criteria in deciding about the letter sequence. The seven stars of the Big Dipper (part of The Great Bear) have been given Greek letters (α, β, γ, δ, ε, ζ, and η) in the order that they appear in the dipper, from right to left, disregarding the
60
Figure 5. The constellation of Sagittarius, as shown in Uranometria by Johann Bayer (Augsburg, 1603). Note that the two faint stars α and β, in the front right leg, are shown as the brightest stars in the constellation, while they both are rather faint (magnitude 4).
A very interesting and beautiful
differences in brightness. Anoth-
atlas was published in 1627 by
er example is Sagittarius, where
Julius Schiller, a Roman Cath-
the letters α and β are assigned to
olic lawyer also from Augsburg
Rukbat and Arkab, both 4th mag-
in Germany. Schiller’s atlas was
nitude stars in the most southern
called Coelum Stellatum Christia-
part of the constellation. In spite
num, or The Christian Sky. All the
of all arguments about this, it is
pagan gods and goddesses are
interesting to see that on Bay-
removed, together with almost
er’s map of Sagittarius, these two
all the other classical figures,
rather faint stars are shown as
their places taken by new con-
being the brightest stars in the
stellations based on figures from
constellation (figure 5).
the Bible and the Christian tradi-
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History of Astronomy | Uranography
tion. The 12 constellations of the zodiac are now the 12 apostles. The sky north of the ecliptic is dedicated to the New Testament, while the south of the ecliptic only figures from the Old Testament are shown. The large constellation Argo (or Argo Navis) was renamed a few decades earlier by Petrus Plancius, who called it Arca Nöe (Noah’s Ark). Plancius also created a new constellation close by called Columba Noachi (Noah’s Dove). These two constellations survived the cleanup by Schiller, together with one southern con-
Figure 6. The flying creature Pegasus, the winged horse, now changed to another flying creature, the angel Gabriël, in Coelum Stellatum Christianum by Julius Schiller (Augsburg, 1629).
stellation from Ptolemy’s list: Ara (The Altar). The real beauty of this atlas can be seen in figure 6. The maps were true pieces of art, and although the idea of a Christian Sky gained some popularity, eventually the classical constellations prevailed. The next major star atlas to be published was Uranographia (or, if you prefer the complete title, Firmamentum Sobiescianum sive Uranographia), by Johannes Hevelius. Published in 1687, this beautiful work almost equals the artistic quality of Schiller’s
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Figure 7. Taurus the Bull as shown in Uranographia, by Johannes Hevelius (Danzig, 1687). Notice that the sky is shown mirror-reversed.
History of Astronomy | Uranography
atlas. One peculiar thing about the atlas (like many others in those days) is that the maps show the sky mirror-reversed (figure 7), a strange phenomenon that originated in the use of sky globes. On a globe of the Earth we see the Earth as it is, with features just as we would see it from space. But the sky can be regarded as a huge, imaginary sphere with the observer inside. In other
Figure 9. Auriga the Charioteer as portrayed by Johannes Hevelius in his Uranographia (Danzig, 1687).
words, we look at the inside of that sphere, while a sky globe is
they would appear from outside
viewed from the outside. So when
the imaginary sphere; that is,
a skyglobe was created, the stars
mirror-reversed (figure 8).
and constellations were shown as
Without any reason that we can determine today, this mir-
Figure 8. Sky globe by Gerard Mercator (1551).
ror-reversed sky is also shown on many flat star maps showing just a portion of the sky, like the ones in Uranographia. That mirror-reversed sky had some weird consequences. Many stars were still referred to by the descriptions in Ptolemy’s catalog. Stars are described there as being in the right knee of Andromeda or in the
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History of Astronomy | Uranography
left shoulder of Orion. On a mir-
them from becoming invisible
ror-reversed map, left becomes
(figure 9).
right, and vise versa. To avoid
The next landmark the British
confusion about left and right,
astronomer John Flamsteed’s
many of the figures were turned
Atlas Coelestis, published in 1729.
around, so on these maps, you
It is one of the first atlases that
see the backsides of Andromeda,
used the equatorial coordinates
Orion, and many more. Look-
and grid, while most older at-
ing at Auriga (the Charioteer)
lases used mainly the ecliptic
in Hevelius’ atlas, there is an-
coordinates. But the ecliptic grid
other remarkable thing: Auriga
is also shown, running at a slant
holds three goats to his breast,
(figure 10).
but since the Charioteer was
The name Flamsteed is still
turned around, the goats had to
well-known today, owing to
be moved to his back to prevent
the “Flamsteed” numbers—an
Figure 10. Ursa Major (The Great Bear) in Atlas Coelestis by John Flamsteed (1729). Note the double coordinate grid.
alternate way of identifying the brighter stars inside a constellation. The numbers go in order of right ascencion, and many stars are referred to today by their Flamsteed number, e.g., 61 Cygni, star number 61 in the constellation of Cygnus. Many stars have both a Greek letter (assigned by Bayer) and a Flamsteed number. But here we have yet another misconception. Only Greek letters can be found on Flamsteed’s maps; and there are no Flamsteed numbers. What
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Coelestis. It was a simplified version of Flamsteed’s atlas, and it also contained the catalog with those Flamsteed numbers. The only new thing to the atlas is the introduction of constellation boundaries, which are also shown in his second atlas, Uranographia. It set new limits. For the first time stars not visible to the naked eye are shown, and Bode uses chart projections Figure 11. Orion, Taurus, Gemini, and Canis Minor in Uranographia by John Elert Bode (1801). Bode uses properly constructed conic projections, which were far superior to the sinusoidal projection that was used on many earlier star charts.
happened is that in a French edition of the atlas and in the catalog, the editor, Joseph JĂŠrĂ´me de Lalande, assigned these numbers to the stars in the catalog. So it was not Flamsteed who introduced the Flamsteed numbers, but Lalande! One more star atlas to mention in this overview is again from a German astronomer, Johann Elert Bode. His Uranographia, published in 1801, was actually his second atlas. In 1782 he published an atlas with the title Vorstellung der Gestirne, or Atlas
64
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that are far superior to everyFigure 12. A detail from the Bonner Durchmusterung star charts (Bonn, Germany, 1863). The chart shows part of the constellation Taurus with the open star cluster the Pleiades.
History of Astronomy | Uranography
thing done before. Bode uses
as representing the transition
mainly conical projections, and
from the classical to the modern
consequently, the atlas shows
star atlases. All naked-eye stars
the stars and constellations with
are drawn in an attrative style
less destortion than most of its
and with an unusual accuracy.
predecessors (figure 11). Bode’s
The classical figures were still
Uranographia was an important
drawn in but with less promi-
step toward the more “modern”
nence than in the earlier atlases.
star atlases of the 19th and 20th centuries.
The Transitional Phase
After that, together with a group of assistants, Argelander created a catalog with the positions of 325,000 stars, down to
The German astronomer Frie-
approximately magnitude 9.5.
drich Wilhelm Argelander pub-
All positions were measured
lished his Uranometria Nova in
from visual observations, and
1843. This atlas is often regarded
the catalog covered the sky from the North Celestial Pole to declination -2°. The positions from the catalog were used to create 37 large star maps. This monumental work became known as the Bonner Durchmusterung, first published in 1863 (figure 12). After Argelander died in 1875, his work was continued to declination -23° by one of his assistants, Eduard Schönfeld. His work became known as the Südliche Bonner Durchmusterung and was published in 1886. The final
Figure 13. Detail of one of the charts of the SAO Star Atlas (SAO, 1969), also showing the Pleiades in Taurus.
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two parts of this work, the Cordoba Durchmusterung, were compiled in Córdoba, Agentina, and
History of Astronomy | Uranography
published in 1908 (to declination
beautiful artistic work of the old
-62°) and in 1930 (to the South
days. Looking at the maps of the
Celestial Pole).
SAO Star Atlas, you do not even
Argelander’s work remained unsurpassed until the 1960s. Then
see the names of those classical constellations. During the last part of the 19th
a comparable work was published by the Smithsonian Astophysical
century and into the 20th centu-
Observatory, or the SAO, in four
ry, another need arose. More and
volumes, containing the accu-
more star enthusiasts could af-
rate positions of about 260,000
ford to buy a small- or medium-
stars. Using these positions, and
sized telescope, and for those
using—for the first time—com-
amateur astronomers, easy-to-
puter plotting techniques, 152 star
use star atlases were needed to
charts were created: the SAO Star
help them navigate the sky and
Atlas (figure 13).
find interesting objects.
There was nothing left of the
But that is another story.
PA
About the Author Wil Tirion is a Dutch uranographer (celestial cartographer). His most famous work, Sky Atlas 2000.0, is renowned by astronomers for its accuracy and beauty. The second edition of his most complete work, Uranometria 2000.0, was published in 2001 by Willmann-Bell. Tirion is also responsible for the sky charts found in many other publications. He was originally a graphic designer. The minor planet (asteroid) 4648 Tirion is named after him.
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Astrophotography
By Martin Griffiths
N
ebulae are one of the most abundant objects for amateur astronomical study and are very rewarding to photograph. A bright nebula can be counted amongst
the most inspiring splendors nature has to offer. What’s more, they are generally very diverse, with a wide range of dimensions, magnitudes, and availability to small telescopes. Nebulae are fascinating; what could be more wonderful than observing these celestial objects, contemplating a snapshot in time of stars being born, imagining the emergence of planetary systems, and dreaming that, in some well-developed areas, the bombardment of surfaces may become conducive to life? Their ethereal nature, short lifetimes, and range of forms make observing them a truly pleasing study.
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“
There is nothing quite like the sight of a glowing patch of gas in the eyepiece to start
�
the imagination...
Astrophotography | Nebulae
A Brief History of Nebulae In the ancient world, the first book to mention nebulae that survived—and was used for almost one and a half millennia—was the Almagest by the Alexandrian astronomer Claudius Ptolemy. This text included seven nebulous objects, three of which were starry asterisms, but not physically related objects. Two were taken from Hipparchus’ existing catalog of fixed stars, and two were new: one is now known colloquially as Ptolemy’s cluster and is the star cluster recorded as Messier 7; the other makes up most of the constellation of Coma Berenices, the star cluster Melotte 111. However, it must be emphasized that these are not nebulae in the true sense of the word; in pre-telescopic times these were unresolved clusters of stars, not collections of gas and dust. The first person to recognize and discover a nebula in the true sense of a gaseous cloud was Nicholas de Peiresc, who saw the Orion nebula in 1610. It is notable that it is also the first deep sky object ever discovered with a telescope, though Galileo did note that the Beehive cluster in Cancer could be resolved into stars— not a true nebula in any sense. He did, however, observe the Orion nebula without noticing a gaseous component. That the true nature of nebulae was still a mystery and not identified as gaseous clouds can be seen from the claim of Simon Marius on his discovery of the Andromeda galaxy in 1612, the first person in the West to record the object. With the advent of spectroscopes and photography, large nebulous areas were revealed
An illuminated leaf from Ptolemy’s Almagest, in French, Bibliothèque Nationale, Paris, 1213 Manuscript.
as clouds of hydrogen gas and silicate and carbonate dust within the Milky Way. It was John Herschel who made the supposition midway through the 18th century that nebulae and star clusters were intimately connected and described the nebulae as being
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the “chaotic material of future suns,” a phrase that turned out to be very prescient. It was the great American astronomer Edwin Hubble who finally made the connection between HII regions, dark nebulae, reflection nebulae, and the stars that illuminate them in a seminal paper
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NASA’s Spitzer and Hubble Space Telescopes teamed up to expose the chaos that baby stars are creating 1,500 light years away in a cosmic cloud called the Orion nebula. Image courtesy of NASA.
Astrophotography | Nebulae
entitled The Source of Luminosity in Galactic Nebulae, published in the Astrophysical Journal in August 1922. Here he showed that the ionization from bright stars led to the emission lines of the nebulae, and he supposed that dark nebulae and reflection nebulae were areas of sky where the illumination was coming from stars newly born or, in the case of dark nebulae, were as yet unilluminated, as stars were yet to form in them. Later studies in the late 1920s and into the 1930s by Otto Struve, Herman Zanstra, Phillip Keenan, and others showed the nature of reflection nebulae in such objects as the Pleiades and the nebulae in Orion, Messier 78. Today we can understand the connection between the true nebulae and objects of many kinds, such as star clusters and individual stars, too.
Nebulae There is nothing quite like the sight of a glowing patch of gas in the eyepiece to start the imagination on a train of thought that leads right down to the production of you and me here on Earth. Nebulae are usually taken to be emission regions of glowing gas illuminated by newly formed stars. However, there are other types, some of which are wonderful objects in their own right, such as planetary nebulae, the death of stars with masses close to that of the sun. By definition, nebulae are patches of gas or “clouds,� but that hides the distinctiveness of each type. Nebulae can therefore be divided into emission nebulae, planetary nebulae, dark nebulae, and reflection nebulae. Although there are also special subsets, such as supernovae remnants, the main types here are recognized by professional and amateur astronomers alike. No matter what nebulae one may pick, they are all intimately tied to the stellar evolution process. Stars experience stages of birth, growth, middle age, old age, and finally death. Astronomers talk of these stages as progressive stellar evolution. They begin with dark, emission, and reflection nebulae and generally end with a planetary nebula or the expanding mass of a supernova explosion. Stars are the only entities in
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our universe that follow the strict rule of evolution, slowly changing with time, but they always remain stars for the majority of their lives.
Image of the Great Rift, a dusty lane that stretches from the constellation Cygnus to Sagittarius. Image courtesy of NASA.
Before stars begin to form in emission nebulae, their materials are corralled together in large molecular clouds which are warm yet unlit collections of basic gas and dust. These molecular clouds can be enormous, stretching hundreds of light years across and having masses of millions of times that of our sun. Being so large, one would think that it would be easy to see such clouds, but by their very nature, anything that does not emit light in the blackness of space is going to be difficult to spot. Most of the dark nebulae studied in our galaxy are known as
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“Barnard objects” after Edward Emmerson Barnard, the man responsible for identifying them by means of photography at Mount Wilson. Approximately 80 of E. E. Barnard’s dark nebulae are half a degree or larger in size. To see them, they require contrast against the starry backdrop of the Milky Way, and so a large field of view or the naked eye is best for seeing many of them. Examples such as the coal sack in the southern hemisphere or the Cygnus rift in the northern hemisphere are ones that spring to most minds. In many cases a pair of binoculars will suffice for most dark nebulae, though photography brings them out beautifully against the starry canvas of our galactic home. Some of the best examples of dark nebulae are B33, the Horsehead Nebula in Orion, Le Gentil’s nebula in northern Cygnus, and the lovely B59, the Pipe Nebula in Ophiuchus. As materials collapse and condense inside molecular clouds, local condensations lead to the production of protostars and eventually new stars. These newborns are highly energetic, and their radiation energizes part of the molecular clouds until they begin to shine of their own accord. We see such areas as emission nebulae. Astronomers label emission nebulae as HII regions, or ionized hydrogen clouds, which really are the glowing nurseries of stars and planets and are full of the materials necessary for life. Although much of this chemistry is relatively simple, there is enough material in an average HII cloud to make several generations of stars, as can be attested to by examination of many of these wonderful regions. Star clusters are evident in their proximity, and the clouds themselves are lit either by radiant members newly born or are hidden by bars of dust, giving hints of emergence into a new world around them. The Pipe Nebula (composed by B77, B78, and B59) is one of the largest dark nebulae in the sky (7°!). In this field of view are also well visible many other dark nebulae in that intricate network that is the central Milky Way. Ionized hydrogen regions are very widespread across the Milky Way and can even be seen in some external galaxies such as NGC
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604 in the Pinwheel Galaxy, Messier 33. However, not all of them are bright and obvious for the visual observer, and some respond better to photographic efforts than to mere viewing. The subtle red colours of most nebulae are not seen visually as the eye does not discern red easily in the dark, and most objects are fainter than expected.
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The Pipe Nebula (composed by B77, B78, and B59) is one of the largest dark nebulas in the sky. In this field of view are also visible many other dark nebulae in the network that is the central Milky Way. Image courtesy of Yuri Beletsky (Las Campanas Observatory, Carnegie Institution for Science).
Astrophotography | Nebulae
Excellent examples of HII regions are the winter glory of the Orion Nebula M42/43 and the Rosette Nebula NGC 2237 in Monoceros. In summer skies, the wonderful M8 and M20 in Sagittarius or M16 and M17 in Serpens are visited reg-
The Rosette Nebula (also known as Caldwell 49) is a large, spherical (circular in appearance) HII region located near one end of a giant molecular cloud in the Monoceros region of the Milky Way Galaxy. Image credit: Adam Block and Tim Puckett.
ularly by amateurs. Once stars are fully formed, converting hydrogen to helium, and generally in equilibrium, we see them as clusters of stars. The bright blue light from such stars or clusters is enough to give suffi-
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cient scattering to make the dust visible, and as the light is of short wavelengths, the frequency spectrum of many reflection nebulae is similar to that of the illuminating stars. Reflection nebulae are not particularly rare, but their relatively low light profile in comparison to light-emitting nebulae, such as HII regions, make them a little harder to see, and the nebulae are generally well located close to the stars. This makes the starlight overwhelming on occasion and renders visual representation of such nebulae difficult. Examples such as the Pleiades or many of the Messier numbers, such as M36–M38 in Auriga, show us how stars born in HII regions stay together for long periods before interaction with the galaxy thins them out into individuals. It is when the stable relationship of hydrogen burning ends that stars begin the next process of nebula formation—dying in a planetary nebula or exploding as a supernova.
Stellar Death and Nebulae This ending depends on the mass of the star. A star larger than 15 times the mass of our sun will become a supernova, while those under this limit will become planetary nebulae. Most stars convert hydrogen to helium for millions or even billions of years, but once the hydrogen begins to run out, the star is doomed. Once there is sufficient helium buildup in the core to significantly interfere with the hydrogen reactions, the core shuts down and begins to contract. However, there is a lot of latent energy in the overlying layers from radiation attempting to escape the outer envelope. As a consequence of this radiation pressure, the star will begin to expand, as gravity works primarily upon the greater mass of the core and only has a relatively weak effect on the outer layers. At this point the core contracts, the outer layers expand, and the star begins to cool. As it does this, the star changes color and cools to become an orange K type sub-giant. The star then utilizes the energy of hydrogen-helium conversion, which now takes place in a shell around the inert hydrogen core rather than throughout the core as in its
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previous incarnation. Over time the star will continue to expand and cool until it becomes an M type red giant. It is now large and luminous, and it has an extensive solar wind, which is driving the material of the outermost layers off the star. This expulsion of material is important in the development of a planetary nebula. Under such forces, a star can lose as much as 1/100,000th of a solar mass per year. Eventually, gravity compresses the helium core until sufficient pressures and temperatures build up inside to fuse helium to carbon. Once a new source of energy has been established, the star has a short stay of execution. However, there is insufficient helium fuel to power the star, and as this fuel becomes exhausted, the outer layers expand again with latent energy from the radiation release and they are eventually pushed off the star, lost to space with an increase in the power of the stellar wind at this stage. Once the luminous outer envelope of the star is lost, the naked core is all that is left: a small, hot remnant with a fraction of the luminosity of the whole star, and the object dims appreciably and makes its way rapidly, ending its days as a white dwarf. That is what planetary nebulae are—the thrusting away of the envelope and the exposing of the white dwarf remnant. Observing planetary nebulae is not particularly difficult, as there are several good examples for amateur study. The Messier objects M27 and M57 in Vulpecula and Lyra are beautiful objects that stand out against the starry backdrop of the Milky Way, while M97 in Ursa Major, NGC 7662 in Andromeda, and NGC 6543 in Draco are lovely examples of their type. Conversely, the death of a massive star is a relatively rare event. This is partly because such stars are rare in numbers within the galaxy. Nevertheless, there are enough of these rare but exciting objects to become worthy of study, and they generally give themselves away due to the expulsion of materials in shells or nebulous clouds. Stars such as Wolf-Rayet types have large UV excess or are termed Luminous Blue Variables (LBV) and are great candidates for supernova explosions. Massive stars which are ending their lives as
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red giants, such as Betelguese in Orion, are also appropriate candidates for spectacular
Dumbell Nebula (Messier 27). Credit: Reinhold Wittich.
explosions. Massive stars continue the fusion process from hydrogen to helium, through carbon, oxygen, nitrogen neon, aluminium, silicon, and others right up to the iron stage. Once the silicon is turned to iron in the core, the last (exothermic) process that holds the star up against gravity is over. To make iron fuse into the next generation of heavier elements it is necessary to inject energy into the star, as the process is endothermic—it needs energy just to keep going. No energy is available at this stage, and so the core falters and is squeezed by the overlying layers, and the materials break down, allowing a huge implosion of the core. This implosion rebounds, and the outer layers falling in under gravity are met by an enormous
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shock wave, which causes the formation of elements heavier than iron on the periodic table in a process known as explosive nucleosynthesis. The resultant explosion of the star spreads its outer layers into space at a very rapid acceleration—up to 60,000 km a second—and the light from the explosion is so bright that it can outshine entire galaxies for a brief period.
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This new Hubble image—among the largest ever produced with the Earth-orbiting observatory—shows the most detailed view so far of the entire Crab Nebula. The Crab is arguably the single most interesting object, as well as one of the most studied, in all of astronomy. Taken with Hubble’s WFPC2 workhorse camera, this image was assembled from 24 individual exposures taken with the NASA/ESA Hubble Space Telescope. Courtesy of NASA.
Astrophotography | Nebulae
The expanding gasses may be lit by radiation for a few months and by the conversion of Ni56 to Fe56, but the light fades eventually to leave an expanding patch of gasses. The core at this stage either becomes a black hole, dependent on how much mass has been shed by the core over the last gasps of its lifetime, or a neutron star like the one in the Crab Nebula. The synchrotron
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Gallery of author’s own images. Clockwise from top left: Messier 42, 43 Messier 20, 21 Messier 8, 20, 21 Messier 16
Astrophotography | Nebulae
radiation from the neutron star, which has now become a pulsar, is then responsible for the ionization of the expanding nebula. By their brief and ethereal nature, there are very few supernova remnants available for amateur study. The best known examples are the Crab Nebula in Taurus and the Veil Nebula in Cygnus.
Conclusion Nebulae come in all shapes, sizes, and different brightness. Some will be right at the edge of your observing ability, while others will be well within reach. The application of photography by many amateur astronomers today renders images which would challenge those from a major observatory only 50 years ago. The life cycle from gas cloud to star back to gas cloud is a reminder that the universe is constantly recycling materials, and that the rubbish of yesteryear is actually the future of stars, planets, and possibly even life elsewhere. Getting to know and appreciate their beauty and their stories gives us a fresh perspective on our place in the cosmos and an endless vista of wonderful objects to observe.
PA
About the Author Martin Griffiths is an enthusiastic science communicator, writer, and professional astronomer. He is a recipient of the Astrobiology Society of Britain’s Public Outreach Award (2008) and the Astronomical League’s Outreach Master Award (2010). He is currently an astronomer at the University of South Wales in the UK and a consultant to the Welsh Government through his involvement with the Dark Sky Discovery initiative, enabling public access to dark sky sites in association with Dark Sky Wales, Dark Sky Scotland, and Natural England. He was also responsible for surveying the sky quality of the Brecon Beacons National Park in their successful bid to gain International Dark Sky Association Dark Sky Reserve status in 2013, and he is a consultant to the Hay Tourism Board for their annual dark sky festivals. Griffiths is the director of the Brecon Beacons Observatory, a public and education resource, fitted with a 30-cm telescope situated in the Dark Sky Reserve. He is also a fellow of the Royal Astronomical Society; a fellow of the Higher Education Academy; and a member of the Astrobiology Society of Britain, the European Society for the History of Science, the British Astronomical Association, the British Science Association, and the Webb Deep-Sky Society.
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Telescopes
A
stronomy has reached a fascinating point. Several new, extremely advanced telescopes will come online in the next few years that are likely to change forever our
view of the cosmos. These instruments will be so powerful that they will completely overshadow today’s telescopes.
Will they show us that we are not alone in the universe? By Geoff Cottrell
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Telescopes | The Next Telescopes
With them we will be able to see
Big Bang, and studying them is crit-
further back in time to the Big Bang
ical to understanding galaxy forma-
than ever before and scrutinize the
tion and evolution. Their light has
atmospheres of exoplanets for evi-
not only been strongly redshifted by
dence of extraterrestrial life. In this
the cosmic expansion (draining away
article I will outline how key scien-
the energy of the photons), but the
tific questions and technologies have
inverse square law has also diluted
shaped the coming new generation of
its intensity. A candle seen 20 feet
space and ground-based telescopes.
away is only a quarter as bright as
The last 400 years have seen the telescope develop from the simple spyglass, a pair of lenses mounted
Bigger is Better
in sliding tubes, to highly sophisti-
In 1928, George Ellery Hale, the as-
cated 10-meter instruments, capable
tronomer, entrepreneur, and builder
of tracing the orbits of hapless stars
of several world-leading telescopes
caught in the thrall of the supermas-
wrote: “Starlight is falling on every
sive black hole lurking at the heart of
square mile of the Earth’s surface, and
the Milky Way. As the pace of astro-
the best we can do at present is to gather
nomical discovery quickened during
up and concentrate the rays that strike
the 20th century, each question
an area 100 inches in diameter.”
answered has raised new ones. The
While the numbers have changed,
key questions in astronomy today
the message remains. Hale was right
are: what is dark matter; what is dark
to recognize that one of the most im-
energy; how did the first galaxies form;
portant parameters of a telescope is
and, are there habitable, Earth-like ex-
its aperture, D. The captured flux of
oplanets? This includes the search for
photons is proportional to the aper-
biomarkers—signs of the molecules
ture area, D2. The two 10-meter Keck
of prebiotic life.
telescopes (Fig. 1), although built in
Many of the biggest challenges
83
one 10 feet away.
1992, embody many design features
faced by the next telescopes come
found in the next telescopes. Each
from the need to detect the faint
collects five million times as much
light from enormously distant galax-
light as the human eye, a figure that
ies. These are young objects, formed
will increase by over a factor of 10 in
less than one billion years after the
the next telescopes.
popularastronomy.com | Fall 2017
Telescopes | The Next Telescopes
The second important parameter
ing the information needed to sharp-
of a telescope is angular resolution, a
en the image. AO systems, originally
measure of the smallest angle it can
developed for the military in the
discern. For a space telescope, the
1970s, now enable telescopes to at-
resolution is ultimately limited by
tain diffraction-limited resolution.
the diffraction of light to λ/D where
There have been huge improve-
λ is the wavelength of the light. This
ments in detectors. Modern imaging
relation suggests that the resolution
detectors are based on charge-coupled
can be made arbitrarily small if the
devices (CCDs) arranged as mosaics
aperture is large enough. However,
covering the image plane of a tele-
Earth-bound telescopes suffer from
scope. CCDs convert virtually every
the blurring effects of atmospheric
photon striking the micron-sized pix-
turbulence, which distorts the in-
els into photoelectrons that are stored
coming wavefronts. The aperture
and read out into memory. One of the
need be no bigger than eight inches if
largest CCD cameras (the size of a car)
all that is required of it is resolution.
will be in the 8.4-meter Large Synop-
To correct for the atmospheric
tic Survey Telescope (LSST), currently
blurring, large telescopes use adap-
under construction in Chile and due
tive optics (AO) systems, firing lasers
to start operation in 2019. This state-
tuned to the frequencies of sodium
of-the-art camera has a total of 189
atoms. These create artificial stars
CCD (4k x 4k pixel) imaging sensors
high above the atmosphere, provid-
(3.2 Gigapixel) and will be cooled to −100°C to reduce thermal noise.
Figure 1 n The twin Keck telescopes located at an elevation of 4,200 meters on Mauna Kea in Hawaii.
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Noise, the enemy of weak signals, comes from several sources. The
Telescopes | The Next Telescopes
most important of these are: ther-
OWL—or Overwhelmingly Large
mal noise in the detectors (hence the
Telescope. Because it is not possible to
cooling), extraneous radiation from
fabricate a monolithic mirror of this
the mirror and body of the telescope
great size, the plan was to divide the
(particularly important at infrared
mirror up into many hexagonal seg-
wavelengths), and the sky back-
ments, each being a part of a much
ground. To detect a weak source, we
bigger paraboloidal surface.
need to collect as many photons as
The segments would be finely po-
possible and concentrate them into a
sitioned using actuators and com-
pixel. The flux of photons collected by
puter control. It turned out that the
a telescope is proportional to D2, and,
OWL was shelved, for complexity and
for a diffraction-limited telescope,
budgetary reasons. But the segment-
the diameter of the image of a point
ed mirror concept had already been
source is proportional to l/D. The area
proven on several highly productive
of the image spot therefore varies
telescopes, like the Keck telescopes
as 1/D2, and so the photon flux on it
(Fig. 2). This technology is the fa-
increases as the fourth power, D4, of the aperture. Size really does matter. This steep dependence underlines the importance of both large aperture and high resolution, a combination that is borne out by the phenomenal success of the Hubble Space Telescope (HST). Orbiting 600 km above the Earth in the most perfect vacuum of space, the HST’s 2.4-meter mirror achieves its diffraction-limited resolution (0.05 arc seconds, or 14 millionths of a degree).
Extremely Large Telescopes In 2005 the European Southern Observatory (ESO) conceived a design for a 100-meter telescope—the
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Figure 2 n Bird’s-eye view of the Keck II telescope’s primary mirror, showing the hexagonal segments and a man’s reflection, for scale. Credit: Laurie Hatch Photography, www.lauriehatch.com.
Telescopes | The Next Telescopes
vored way to make Extremely Large
placed astride the telescope. The
Telescopes (ELTs).
field of view will be one third of the
Three ELTs are planned to come
width of the full moon, and the whole
online in the next decade. The largest
moveable altazimuth structure will
of these, the ESO’s European Extreme-
weigh 3,000 tons.
ly Large Telescope (E-ELT, Fig. 3), is
Another segmented mirror ELT is
a scaled-down version of OWL, with
the Thirty Meter Telescope (TMT),
a 39-meter segmented mirror. It
which will be sited either on Mau-
will be built on Cerro Armazones in
na Kea or on La Palma in the Canary
Chile at an altitude of 3,060 meters.
Islands. A different technology will be
The E-ELT is expected to achieve a
used in the Giant Magellan Telescope
resolution of 0.01 arc seconds at a
(GMT), which will collect the light
wavelength of 2 mm. There will be
from seven 8.2-meter honeycomb
two sideways-pointing foci, with
mirrors and focus it onto a com-
spectrometers and cameras borne on
mon focal plane (equivalent to one
platforms the size of tennis courts
22-meter telescope). To make a honeycomb mirror, glass
Figure 3 n Artist’s impression of the European Extremely Large Telescope (E-ELT). Note the relative size of the cars.
86
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is melted in a huge rotating furnace. Isaac Newton realized that the surface of a spinning bucket of water
Telescopes | The Next Telescopes
naturally assumes a paraboloidal
light from distant background gal-
shape. This is what happens in the
axies graze past concentrations of
honeycomb mirror, except that when
mass—clusters of galaxies or regions
the glass is cooled the dish shape
containing dark matter, for exam-
is frozen in. The rear surface of the
ple—the light is bent. This bending
mirror has honeycomb-shaped in-
distorts the optical images of the
dentations to reduce both the weight
background galaxies, an effect called
(without sacrificing strength) and the
gravitational lensing. The LSST will
thermalization time.
gather lensed data that will reveal
Making Movies of the Cosmos
sensitivity of the LSST will enable it
While the ELTs will extract a great
to see so far back in time that it will
deal of information from small sky
be able to determine the distribution
targets, there is a complementary
of dark matter as a function of red-
role for survey telescopes with wider
shift, and so trace its time evolution.
fields of view. The Large Synoptic Surror design giving a field of view of
The World’s Largest Scientific Instrument
3.5°, equivalent to 50 full moons.
Imagine a telescope with an aperture
vey Telescope has a novel three-mir-
The LSST will survey the same huge
of a million square meters, bridging
tranche (10,000 square degrees) of
two continents. Science fiction? No,
the southern sky every three days, in
science fact. And it is embodied in
effect enabling it to make “movies”
the Square Kilometer Array (SKA) radio
of 10 billion stars and galaxies. The
telescope, which will extend from the
telescope will discover many tran-
Karoo region of South Africa to the
sient objects, for example: superno-
Murchison region of Western Austra-
vae, near-Earth objects, and variable
lia. The SKA is expected be completed
stars. Objects that change position
in the mid-2020s. The sites have been
or brightness will trigger alerts for
selected on the basis of their sparse
other telescopes to follow up in more
populations, since electromagnetic
detail within minutes.
quietness is essential. The SKA will
In 1915 Einstein showed how space
87
dark matter distributions. The high
expand the sensitivity, resolution,
is curved by mass, and how curved
and spectral coverage (50 MHz to 20
space bends light. When the rays of
GHz) of existing radio telescopes by
popularastronomy.com | Fall 2017
Telescopes | The Next Telescopes
over 10 times, and will transform our
a smaller pathfinder telescope called
view of the universe.
MeerKAT (Fig. 4).
Radio wavelengths are a million
In Australia, the SKA-survey tele-
times longer than those of light, so
scope will use similar dishes to SKA-
the diffraction-limited resolutions
Mid, and these will be equipped with
of even large single dishes are limit-
phased-array feeds (PAFs). In a PAF,
ed. The way to make high-resolution
the focal plane of one dish is popu-
observations at radio frequencies
lated with an array of detectors con-
was pioneered in the 1960s by link-
nected to a central site. The elements
ing up pairs of dishes, as interfer-
will form a phased array, creating
ometers, to form elements of a much
a pattern of radio beams, viewing
larger simulated antenna (aperture
different parts of the sky, and speed-
synthesis). Powerful computers are
ing up sky surveys. In the Australian
needed to transform the information
Square Kilometre Array Pathfinder
from such an array of antennas into
(ASKAP) radio telescope, the PAF
usable images.
concept is currently being tested as
In South Africa, SKA-Mid will consist of a large aperture synthe-
part of an array of 36 12-meter dishes at frequencies of 0.7 GHz to
sis array of 250 15-meter paraboloidal radio dishes operating in the range 350 MHz to 15 GHz. There are three groupings. The most compact of these is a five-kilometer dense “core” of antennas, providing half of the collecting area. Outside the core is an intermediate group, reaching distances of 180 km. An outer array, along winding spiral arms, will extend to 3,000 km. Think of these outer groupings as representing a “zoom” lens on a camera, and the central core more like a sensitive “close-up” lens. A section of the array is already under construction:
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Figure 4 n Aerial view of the SKA and MeerKAT dishes in South Africa. Courtesy of the SKA Organisation
Telescopes | The Next Telescopes
1.8 GHz, and covering a 30 square
enough to detect an airport radar on
degree area of sky.
a planet 50 light years away. Within
Also in Australia will be a “software telescope.� SKA-Low is a low
similar to the sun, many of which
frequency (50 to 350 MHz) aperture
may possess Earth-sized planets.
array with 250,000 separate simple
The sensitivity of the SKA also
low-cost antennas, each able to see
makes it well suited to finding faint
the whole sky and having no moving
transient sources, such as pulsars
parts. Each antenna is connected
in galaxies. The number of known
to a central correlator with enough
pulsars is around 2,000, a figure that
fiber-optic cable to girdle the Earth
is likely to increase 10 times with the
twice. The array will be phased
SKA. Precise timing measurements
using software to form steerable
of pulses from a large ensemble of
beams. Like SKA-Mid, most of
pulsars should reveal any spacetime
the antenna elements are densely
distortions arising from gravitational
packed in the central two km of the
waves. This will complement mea-
array, and there are also others 50
surements of gravitational waves
km away on spiral arms, providing
from merging black holes, first
the fine scale information.
observed by the Laser Interferome-
The SKA will be well positioned to address the key astronomy questions, and it will also open up new fields.
89
this distance there are over 100 stars
ter Gravitational-Wave Observatory (LIGO) in 2015.
For example, it will probe the cosmic
Into Space
dawn of the universe, over 13 billion
The next decade will see the launch
years ago, by observing 21-centi-
of new space telescopes. The Wide-
meter radio waves from primordial
Field Infrared Survey Telescope
neutral hydrogen clouds, redshift-
(WFIRST) satellite is planned for
ed to a wavelength of a few meters.
the mid-2020s. It will, like Hub-
The Cradle of Life project will utilize
ble, use a 2.4-meter mirror but will
spectroscopy to search for prebiotic
survey a region 100 times larger at
molecules, the building blocks of life,
wavelengths of 0.6 to 2 mm. The
such as amino acids. The SKA could
observatory will survey galaxies
detect possible extraterrestrial sig-
and clusters of galaxies, and it will
nals; its antennas will be sensitive
infer the distribution of dark matter.
popularastronomy.com | Fall 2017
Telescopes | The Next Telescopes
When a star passes directly in front of
the cosmos. But some of the most
another star, the light of the latter is
important are its “deep fields.”
brightened slightly—an effect called
These show that the first galaxies
gravitational microlensing. If the
to form looked very different from
foreground star also has a planetary
today’s more mature ones. When
system, it is possible to obtain infor-
galaxies form, they contain new,
mation on the exoplanets, a role to
hot, and massive stars that shine
which WFIRST will be well suited.
brightly in ultraviolet light. Due to
The European Space Agency’s Eu-
the expansion of the universe, the
clid, a 1.2-meter optical/near-infrared
ultraviolet light from these galax-
space telescope, is due for launch in
ies has been redshifted into the far
2020 and will measure a billion gal-
infrared. An infrared telescope is
axies. These data will be used to make
therefore needed to see these galax-
the most detailed map ever of the 3D
ies, and this is the role that the next
distribution of galaxies, dark matter,
large space telescope will fill.
and dark energy for the last 10 billion years of the universe. Euclid’s prima-
5 rocket to launch the HST’s succes-
ry mission is to understand why the
sor, the James Webb Space Telescope
expansion of the universe is acceler-
(JWST, or Webb) in 2018 (Fig. 5). The
ating. The source of this acceleration
JWST is a wholly infrared telescope
is a mysterious dark energy, con-
with a huge 6.5-meter mirror. Webb
stituting 75% of the matter-energy
will also carry sensitive cameras and
content of the universe. If our model
advanced imaging spectrographs for
of the universe is correct, Euclid’s 3D
infrared wavelengths.
map should reveal, imprinted on the
How do you squeeze a 6.5-meter
distribution of galaxies, the mem-
mirror in the nose cone of a rock-
ories of the primordial fluctuations
et? The gold-coated JWST mirror
of matter now expanded to immense
is made from a mosaic of 18 light-
scales of around 2 billion light years.
weight hexagonal beryllium seg-
The James Webb Space Telescope
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We are now preparing for an Ariane
ments that are carefully folded like origami. When the telescope arrives at its Lagrangian point, 1 million
The Hubble Space Telescope has
miles from the Earth and away from
produced many striking images of
the sun, the segments will unfurl,
popularastronomy.com | Fall 2017
Telescopes | The Next Telescopes
like a butterfly emerging from a
cooled, and the telescope will have a
chrysalis, to produce the mirror. The
sunshield the size of a tennis court
mirror will be cooled so that its own
blocking the heat from the sun,
heat does not overwhelm the faint
Earth, and moon.
cosmic light. The telescope’s detec-
Infrared telescopes can see deeply
tors, located in the Integrated Sci-
into the hearts of the dusty clouds
ence Instrument Module, will also be
that lie in the plane of disc galaxies like the Milky Way. This is because
Figure 5 n The James Webb Space Telescope sitting on its sunshield. Credit: NASA/Northrop Grumman.
infrared, unlike visible light, is only weakly scattered by dust grains.
Backpane
ISIM
Optical Telescope Element (OTE) Primary Mirror
Sunshield
OTE Secondary Mirror
Startrackers Spacecraft Bus
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Telescopes | The Next Telescopes
Webb will therefore be able to probe
that include oxygen, carbon dioxide,
interstellar star-forming regions,
and water vapour molecules in the
search for protoplanetary discs, and
atmospheres of exoplanets.
see the emission from organic mol-
In summary, the next telescopes
ecules, delineating star-forming
will strain the limits of what is tech-
regions, such as the Pillars of Creation
nically possible and target the key
with 100 times the resolution of
questions: what is the nature of dark
Hubble. The telescope will also look
matter; what is dark energy; how did
for the direct light from exoplan-
the first galaxies form; and are there
ets and image them using a coro-
habitable Earth-like exoplanets?
nagraph, a disk placed in the focal
The last question is a tremendously
plane to block the dazzling light
exciting one because it includes the
from the host star. Webb will search
search for biomarkers. Will the next
for biomarkers: these are the telltale
telescopes tell us that we are not
fingerprints of extraterrestrial life
alone in the universe?
PA
About the Author Geoff Cottrel began his science career as an astronomer, using the radio telescopes at Cambridge University’s Mullard Radio Astronomy Observatory to observe colliding galaxies. After a period working on fundamental low temperature condensed matter physics (investigating the contact electrification of solidified noble gases) at UMIST, Manchester, he then branched out into plasma physics (not far from astrophysics), moving to the Culham Centre for Fusion Energy and the Joint European Torus (JET) project, working on magnetically confined plasmas. JET is a toroidal magnetic chamber (tokamak) experiment, in which the confined plasma is heated by powerful neutral beams and radio frequency waves to temperatures of 100 million degrees—hotter than the center of the sun. In these experiments, Cottrell identified super-thermal radio emission from energetic fusion-produced alpha-particles. He was director of the Culham International Summer School for Plasma Physics from 2006-2011. He is a fellow of the Royal Astronomical Society, and a visiting scientist at Rutherford Appleton laboratories and at the Oxford University Astrophysics Department. He currently lives in Oxford, where he enjoys making (and writing) music, tackling the challenges of writing about science, and running an observatory in his garden. To learn more or to contact him, visit his website, www.science.geoffcottrell.com.
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Exoplanets
Do there exist many worlds, or is there but a single world? This is one of the most noble and exalted questions in the study of Nature.
T
ake a look at the image in Figure 1 on the next page. It may not look like much, but the four labeled blips of light come from
four planets orbiting a star that lies far beyond our own solar system. This image is therefore part of an incredible scientific revolution that is now underway, one that is helping us under-
stand the answer to the exalted question raised — St. Albertus Magnus (1206–1280)
by St. Albertus Magnus some 800 years ago.
BY JEFFREY BENNETT 94
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Exoplanets | Extrasolar Planets
St. Albert raised the question at a time when Earth was still generally assumed to be the center of the universe. We first learned otherwise about 400 years ago, when scientific evidence collected during the Copernican revolution left no reasonable doubt that Earth is a planet orbiting the sun. This fact opened the possibility that the stars might be other suns with their own planets. Still, as recently as the early 1990s, we did
Figure 1 • This infrared image shows four planets (labeled b, c, d, e) that orbit the star HR 8799. Light from the star itself (center) was mostly blocked out during the exposure, as indicated by the solid red circle. Click on the video icon to see a time-lapse video showing the orbital motion of the planets. Credit: A.-L. Maire / LBTO.
not know for sure whether any
Today we know of thousands, and the number is rapid-
such extrasolar planets, or exo-
ly growing. Indeed, it now seems likely that many—and
planets for short, really existed. Figure 2 • This photo shows the pedestals housing the sun (gold sphere on nearest pedestal) and the inner planets in the Voyage Scale Model Solar System (Washington, DC). The model planets are encased in the sidewalk-facing disks visible at about eye level on the planet pedestals. To the left is the National Air and Space Museum. Click on the web icon to learn how your community can get its own Voyage model.
perhaps even most—of the hundreds of billions of stars in our galaxy have their own planetary systems, and the same is presumably also true among the more than 100 billion other galaxies in our observable universe. All in all, there are probably as many planets (and stars) in the universe as there are grains of sand on all the beaches of Earth combined. Imagine what St. Albert would think now. The scientific revolution of exoplanets is remarkable on many levels, starting with the technological one. To understand the challenge involved, consider what our solar system looks like on a scale of 1-to-10 billion, as it does in the Voyage scale model shown in Figure 2. On this scale, the sun is about the size of a large grapefruit, while the largest planet, Jupiter, is only about the size of a marble and Earth is smaller than the ball point in a pen. Yet while you can walk from the sun to Pluto in just a few minutes on this scale, you’d need to continue the distance across the Unit-
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Exoplanets | Extrasolar Planets
ed States to reach even the near-
looking for small motions of a star caused by the gravi-
est other stars. In other words,
tational tug of orbiting planets. Two major methods can
detecting exoplanets is rather
detect these tugs. The astrometric method seeks to observe
like trying to see ball points or
the small changes that will occur in a star’s position in the
marbles more than 4000 kilo-
sky. This method has had limited success to date, but the
meters away, a problem further
European Gaia mission (launched in 2013) is expected to
compounded by the fact that
change that over the next few years as it continues to mea-
the tiny planets shine only with
sure stellar positions with unprecedented precision. The
light reflected by a star that is
greater success to date, which includes most of the first
typically a billion times brighter
several hundred exoplanet discoveries, has come with the
than they are.
Doppler method, which relies on the same idea used by ra-
Given the observational chal-
dar guns to catch speeders: an object moving toward you
lenge, you probably won’t be
will have the wavelengths of its light (or of reflected radio
surprised to learn that we have
waves used in radar) compressed to shorter wavelengths (a
relatively few actual images
blueshift) and an object moving away from you will have its
of planets like those in Figure
light stretched to longer wavelengths (a redshift). As shown
1. Instead, most of the thou-
in Figure 3, scientists can therefore recognize the existence
sands of known exoplanets have
of orbiting planets by detecting alternating redshifts and
been identified through indirect
blueshifts in the spectra of distant stars.
methods, which fall into two major categories. The first category involves
The second general approach to indirect detection seeks to measure changes in a star’s brightness as one or more orbiting planets pass in front of it as seen from Earth. This is done through what
Figure 3 • The gravity of an unseen, orbiting planet (outer circle) causes its star to trace a small orbit (inner circle) around their mutual center of mass. As a result, if the system is oriented so that the star moves alternately toward and away from Earth, we can, in principle, detect alternating redshifts and blueshifts in its spectrum. Image credit: The Essential Cosmic Perspective, 8th Edition, by Bennett, Donahue, Schneider, and Voit (Pearson, 2017).
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we call the transit method, which works only when a planet happens to orbit edge-on as seen from Earth. In that case, as shown in Figure 4, the star’s light will dim slightly during the time that the planet passes in front of the star as viewed from Earth. The transit method is the current champion of planet discoveries, thanks to the Kepler spacecraft, which used this method
Exoplanets | Extrasolar Planets
to find evidence for some 4,000 planets orbiting some 2,000 stars during its main observing mission from 2009 to 2013. In addition to telling us that a planet exists, these indirect methods can provide us with a surprising amount of information about the planet. For example, all of the methods can tell us a planet’s orbital period and
Table 1 • A summary of the major ways in which we can learn properties of exoplanets.
–––––––––––––––––––––––––––––––––––––––––––––––––––– Planetary Property Method(s) Used to Measure –––––––––––––––––––––––––––––––––––––––––––––––––––– period Doppler, astrometric, or transit Orbital –––––––––––––––––––––––––––––––––––––––––– distance Doppler, astrometric, or transit Properties –––––––––––––––––––––––––––––––––––––––––– eccentricity Doppler or astrometric –––––––––––––––––––––––––––––––––––––––––––––––––––– mass Doppler or astrometric –––––––––––––––––––––––––––––––––––––––––– size (radius) transit Physical –––––––––––––––––––––––––––––––––––––––––– Properties density transit plus Doppler –––––––––––––––––––––––––––––––––––––––––– atmospheric composition, transit or direction detection temperature ––––––––––––––––––––––––––––––––––––––––––––––––––––
distance from its star, while the Doppler and astrometric meth-
methods help us learn about exoplanets.
ods can help us learn the plan-
By combining these physical data with model-based in-
et’s mass and the transit method
ferences, scientists can make predictions about the nature
can tell us a planet’s size. When
of different exoplanets. This idea can be neatly summa-
we have both size and mass in-
rized with a “planetary mass-radius diagram” (or “M-R
formation, we can calculate a
diagram”), as shown in Figure 5. (Readers familiar with
planet’s average density. Table
stellar astronomy will recognize similarities between the
1 summarizes the major ways
ways in which scientists can use this M-R diagram for
in which our planet detection
planets and the ways that astronomers have traditionally
Figure 4 • The central diagram shows a planet orbiting a star edge-on as seen from Earth. The left graph shows the dimming of starlight that occurs each time the planet passes in front of the star; the right graph shows that there is also infrared dimming when the planet passes behind the star, since the planet contributes to the system’s infrared brightness. The data are for a star called HD 189733. Image credit: The Essential Cosmic Perspective, 8th Edition, by Bennett, Donahue, Schneider, and Voit (Pearson, 2017).
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Exoplanets | Extrasolar Planets
Figure 5 • This “planetary mass-radius diagram” shows a sample of exoplanets for which both mass and radius have been
measured (red dots), along with the planets of our own solar system (green dots). Image credit: The Cosmic Perspective, 8th Edition, by Bennett, Donahue, Schneider, and Voit (Pearson, 2017). Paintings by Michael Carroll.
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Exoplanets | Extrasolar Planets
used the more famous H-R di-
many stars have planets. The Kepler mission again holds the
agram [Hertzsprung-Russell di-
key to date, because it made its planetary discoveries while
agram] for stars). Because mass
monitoring a known number of stars. Therefore, based on
and radius together yield densi-
the mission’s technological capabilities, scientists can use
ty, the graph also shows select-
the Kepler data to calculate approximate minimums for the
ed density curves (dashed lines).
percentages of stars that have planets of various sizes.
The planetary mass-radius di-
Figure 6 shows the results, and they are quite remarkable.
agram offers a wealth of infor-
For example, the first bar shows that at least about 17%
mation, but perhaps its most im-
of stars have one or more planets similar in size to Earth.
portant lesson can be seen simply
Keep in mind that these percentages are almost certainly
by noticing the difference in scat-
underestimates that will rise as new technological capabili-
ter among the green dots for the
ties enable us to detect planets that are undetectable today.
planets of our own solar system
(For example, the relatively low percentages for large plan-
in comparison to the red dots
ets are almost certainly due to the fact that these planets
for exoplanets. Clearly, planets
have long orbital periods, making most of them impossible
come in a far wider range of types
for us to have detected during the short time in which we’ve
than we could have known from
been searching for them.)
studying only the planets that
This brings us back to the question we opened with from St.
orbit our sun. For example, no-
Albertus Magnus. Although he could not have had the con-
tice the labels indicating regions of the diagram that represent “hot Jupiters” (Jupiter-like planets that orbit very close to their stars), “water worlds” (planets with compositions dominated by water or other hydrogen compounds, though not necessarily in liquid form), and “super-Earths” (planets with Earth-like composition that are larger or more massive than Earth). In addition to learning about planetary nature, current data allow scientists to make some statistical statements about how
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Figure 6 • Estimated minimum proportions of all stars that have planets of different size
categories, based on Kepler results. Image credit: The Cosmic Perspective, 8th Edition, by Bennett, Donahue, Schneider, and Voit (Pearson, 2017).
Exoplanets | Extrasolar Planets
text we have today, we can guess
is not central to the biological universe.
that by “worlds,” he was proba-
For some, this likely-to-come discovery may be dismay-
bly thinking of worlds like Earth,
ing, seeming to diminish our own status in the universe. But I
with living beings. If so, then we
look at it differently: Using only the power of our bodies and
still do not fully know the answer
brains, we, living here on one small world, will have figured
to his question, because we do
out our true place in the universe. This is an achievement that
not yet know whether any other
should inspire anyone, regardless of whether beings on oth-
worlds are home to life. But look
er worlds have done it before us. We have created something
how far we’ve come. There is
important here on Earth, and it is our job to make sure that
no longer any doubt that worlds
we preserve it, so that our descendants can build upon it and
similar in size to Earth are com-
someday set sail for planets around other stars.
PA
mon, and the fact that many of these worlds also have Earth-like orbits makes scientists suspect that worlds with continents and oceans are also common. With that, it seems only a matter of time until we discover worlds with life. If this occurs, as I expect it will, then we will have finally reached the culmination of the Copernican revolution: We will know not only that our Earth is not central to the physical universe, but also that it
BONUS FEATURES • The following are a “prelecture video” and “narrated figure” that accompany the chapter on exoplanets for the author’s textbooks The Cosmic Perspective (8th edition) and The Essential Cosmic Perspective (8th edition). Similar videos, and a large number of other study resources, are available for all chapters of these books on the Mastering Astronomy website. Access to Mastering Astronomy is included with selected textbook packages from Pearson, which you can find with the following links for The Cosmic Perspective and The Essential Cosmic Perspective.
VIDEO 1 • “Prelecture Overview — Other Planetary Systems”
VIDEO 2 • “The Planetary Mass-Radius Diagram”
About the Author Jeffrey Bennett is the lead author of college textbooks in astronomy, astrobiology, mathematics, and statistics, as well as of numerous award-winning books for children and the general public. His personal website is www.JeffreyBennett.com. Much of this article is adapted from material that appears in the author’s textbook series from Pearson, written along with co-authors Megan Donahue, Nick Schneider, Mark Voit, and Seth Shostak. The series includes The Cosmic Perspective (8th edition), The Essential Cosmic Perspective (8th edition), The Cosmic Perspective—Fundamentals (2nd edition), and Life in the Universe (4th edition). More information can be found under the “textbook” section at http://www.bigkidscience.com/books/.
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Astrophotography
Quitting the
Day Job
By John Read
I spent every day of the previous 10 years in a windowless office, working for a California-based Fortune 500 company that makes cleaning supplies. In March of 2016, I sat down in my director’s office and delivered the news. He sat across from me, tapping a pen on the desk, and glancing awkwardly out his giant window at the corporate parking lot. “I’m moving to Canada to study astrophysics full-time,” I said. At first he didn’t process the statement. In the midst of the 2016 presidential primaries, several folks in the office had been joking about moving to Canada. “You’re staying with the company and,
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How I left the corporate world to follow a passion for astronomy
Astrophotography | Quitting the Day Job
I assume, staying in finance,” he
years away. Though our chance
said. I wasn’t sure it was a ques-
meeting was purely coincidental,
tion. “No,” I answered, “I’m leav-
and we only spoke for a few min-
ing the company.”
utes, the encounter reaffirmed I’d
Cleaning out my office, I found a novelty watch I’d received as a gift,
someone who did exactly what I
the kind that shows the phases of
wanted to do, operating on the
the moon. Just a few months ear-
frontier of astronomy—and what
lier, the director had presented
I believe to be the frontier of the
me with a gold watch, a token of
human condition: the search for
appreciation for 10 years of service
life elsewhere in the universe.
with the company. I stepped back
In order to understand why I was
into the director’s office, hold-
willing to quit my job, I’d like to
ing the astronomical watch. “This
take you back to my journey into
is for you,” I said. “Keep looking
amateur astronomy.
up.” He took the watch (still in its
103
made the right decision. Here was
My space interest solidified as a
original box), smiled, and gave me
10-year-old kid flipping through
a hug. This symbolized the be-
old issues of National Geographic.
ginning of the end of my career in
A nerd growing up, I was obsessed
corporate America.
with Star Trek and chess club, but
Later that week I was seated on
it wasn’t until my mid-20s when
board a United Airlines 737 beside
I bought a $14 telescope at Wal-
Dr. Daniel Angerhausen, a nota-
greens that astronomy became
ble NASA astrophysicist. He wore
a passion. I bought the telescope
large noise-canceling headphones,
after learning that NASA was fi-
and it wasn’t until we landed that
nalizing its LCROSS mission, which
I spoke to him. I broke the ice by
involved crashing a spacecraft into
asking about the NASA patches and
the moon. I set up the telescope
NASA stickers peppering his lap-
outside my apartment, pressed
top, clothes, and bag. Angerhausen
my crappy LG camera phone up
worked on SOFIA, the NASA 747
to the eyepiece, and began film-
embedded with a 98-inch infrared
ing at the precise time the crash
telescope in the fuselage. He is a
was supposed to occur (you can
planet hunter, searching for ex-
watch the video here). Turns out
trasolar planets almost 1,000 light
the crash wasn’t visible from Earth,
popularastronomy.com | Fall 2017
Astrophotography | Quitting the Day Job
objects (https://goo.gl/
Transporting the optical tube of my 12-inch Dobsonian telescope.
JACRu1), some of the brightest deep sky targets. I joined the local astronomy club and volunteered with the club’s outreach team, part of the NASA Night Sky Network. After my first year of volunteering, and attending close to fifty star parties, I discovered but a month or so later, I pointed
that many students actually owned
the same telescope at Saturn, and
telescopes but didn’t know where to
that’s when everything changed.
point them. With this fact in mind,
Seeing the rings of Saturn for the first time is often compared to a
50 Things to See with a Small Tele-
religious experience. It’s just that
scope. The book has been helpful to
damn beautiful. A short time lat-
so many people, and it often sits at
er, I purchased the Meade ETX-60
number one in both the Astronomy
telescope on Craigslist. The un-
and Stargazing sections of Amazon.
derwhelming 60mm diameter lens and shaky computerized mount showed me enough of the heavens to give me “aperture fever,” the desire to own bigger and bigger telescopes. The fever was soon cured with the procurement of a 12-inch Dobsonian telescope, a Eagle Nebula imaged to show a visual representation of the object.
104
I put together my first publication,
scope so big, the optical tube had to be carried on the roof of the car. With ample aperture and a hunger for all things space, I began working through the Messier
popularastronomy.com | Fall 2017
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Astrophotography | Quitting the Day Job
Photographing the International Space Station.
For me, it’s not enough to see the wonders of the universe with my own eyes: I have this unquenchable desire to share my experience with the world via twitter (@johnaaronread) or Facebook (http://fb.me/50ThingstoSeewithaSmallTelescope). On this note, my approach is different than most. I own a computerized German equa-
ing is more effective than tradition-
torial mount, with a refractor capa-
al astrophotography. iPhone images
ble of taking long exposures. How-
of the moon can be done freehand
ever, I rarely photograph the night
(holding the phone up to the tele-
sky with perfection in mind. For me,
scope eyepiece). These moon photos
the joy is in sharing the visual expe-
make great desktop backgrounds.
rience through photography, which
The addition of an iPhone adapter
means finding a way to simulate the
can yield some fascinating results.
visual experience. You can see the
Detailed deep sky imaging (gal-
results in the adjacent image.
axies and nebulae) is typically off
Photographing the Internation-
phone cameras; the CCDs of today’s
favorite experience to share. A
phone cameras simply don’t collect
DSLR camera connected to a tele-
enough protons. However, there
scope produces images like the
are apps that promise to bring deep
one shown at right. A full descrip-
sky into the realm of the phone. I’m
tion of my technique can be found
skeptical but open-minded. One
here. (My apologies for the video
example of such software is called
quality; it was filmed using an
NightCap, and it can be found in the
iPhone in my garage.) Also, avoid
iTunes store. For planetary photography, the
filled with vitriolic (yet amusing)
iPhone, combined with stacking
comments from the Flat Earthers
software and a moon filter, yields
claiming the ISS is fake and that I
impressive results. Most of the
must work for NASA (I don’t).
software required to process and
For several targets, iPhone imag-
105
limits for the current generation of
al Space Station is probably my
the comment section, as it is often
popularastronomy.com | Fall 2017
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stack the images is free. While it is
GET
Astrophotography | Quitting the Day Job
iPhone image of the moon through a Dobsonian telescope.
taught over 8,000 people how to use telescopes at several hundred events), people care more about “seeing cool stuff” than learning about the night sky. That’s just a reality. My book, 50 Things to See with a Small Telescope, and my social media posts ensure that they won’t be disappointed. With that in mind, here are some “enthusiast” tips for taking the telescope experience to the next level:
106
possible to take individual photos of
n The
the planets (I’ve done it on several
dollar are Dobsonians. The downside
occasions), photos of detail must be
is that they’re large. If size doesn’t
stacked. Stacking involves multiple
faze you, check this out: http://
images of the same target layered
amzn.com/B003ZDDP06. Keep in
on top of one another. This tech-
mind, though, the best telescope is
nique masks the noise generated by
the one that you’ll actually use.
high ISOs and low light levels, while
n You
bringing out the subtle details from
lar with a reflector than a refrac-
multiple frames. Photographer An-
tor, but if you’re looking for ultra
drew Symes uses these techniques
portability, crystal-clear views,
with amazing results. Check out his
and eventually a move to deep sky
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here. I get a certain amount of flak
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for not suggesting folks start with
n Typically,
binoculars. Some (strongly) be-
az mounts instead of equatorial
lieve one should learn the night sky
mounts (EQ). Alt-az mounts are
before graduating to a telescope.
simpler, and as I said before, the
Maybe it’s because I’m a millennial,
best telescope is the one you’ll ac-
but in my experience (having now
tually use. EQ mounts at low price
popularastronomy.com | Fall 2017
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Astrophotography | Quitting the Day Job
points are often, well, terrible. If
erture, consider a table stop New-
you are interested in an equato-
tonian like this one: http://amzn.
rial mount, here is the most basic
com/B00463ZK3O.
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n Unless
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your budget is in the
thousands, don’t invest in a go-
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spent on a telescope with a larg-
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PA
About the Author Shortly after receiving his pilot’s license as a Royal Canadian Air Cadet, John Read dropped out of aerospace engineering at Carleton University to pursue a degree (and career) in corporate finance. A few years later, his wife bought him a 12-inch Dobsonian telescope for Christmas. (To be fair, she got leather boots.) He joined the Mount Diablo Astronomical Society, volunteering as many as four nights per week under California’s cloudless skies. During his time at MDAS he began writing essays for the club’s magazine, Diablo MoonWatch, and later published his first book, 50 Things to See with a Small Telescope, an Amazon best seller, which was followed by three additional titles. His Callisto Deception, the sequel to The Martian Conspiracy, will be released fall 2017. He studies astrophysics at St. Mary’s University in Halifax, Nova Scotia.
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History of Astronomy
By Peter Pesic
M
any people interested in science are also keenly interested in music, and vice versa. But what is the connection between music
and science? To a surprising degree, science has been influenced significantly by music. Let me present three important historical examples, ending with a notable recent discovery.
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This influence goes back to the very beginnings of science in ancient Greece. There, the followers of Pythagoras found that music gave the first link between natural phenomena and mathematics, two realms previous considered unrelated (Figure 1). The Pythagoreans noticed that familiar musical intervals were produced by strings whose lengths formed simple whole-number ratios, such as the octave (2:1) and the perfect fifth (3:2). For them, this was the first revelation of how “all is number,” providing the first step in their ambitious program to understand everything using mathematics. Plato took up this program and presented an account of the cosmos as being formed according to musical ratios. In contrast, his student Aristotle argued that number was too rigid and unchanging to describe the organic processes of growth and change that were crucial to what he called “physics.” Indeed, Aristotle’s Physics founded that field and was its main text for over a millennium.
Figure 1 n Images of the founders of music from Francinus Gaffurius, Theorica musicae (1492): Jubal, from the Bible (top left), along with images of Pythagoras (trying bells, glasses, and pipes) and Philolaus.
Drawing on Pythagorean ideas, Plato advanced a whole new conception of education going beyond rote memorization to the study of seven “liberal arts” (as they came to be called), comprising three basic linguistic arts (grammar, logic, rhetoric) and four mathematical arts (arithmetic, geometry, music, astronomy). These mathematical sister arts became known as the quadrivium, the “four-fold way” that became the heart of higher education (Figure 2). As I argue in my book Music and the Making of Modern Science, our natural sciences are the “children” of this divine sisterhood, in which music was an essential part, bridging the purely mathematical (arithmetic and geometry) and the visible (such as astronomy). Higher education to this day still reflects Plato’s radical plan, even though
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most people do not know what the “liberal arts” really were or meant. As late as the time of Isaac Newton, university students studied the classic texts that had over centuries come to represent those arts. For instance, the young Johannes Kepler studied Boethius’ Institutes of Music alongside Aristotle’s Physics. From an early age, Kepler sang
Figure 2 n The quadrivium, the “four-fold path” encompassing the four sister studies central to higher “liberal education”: arithmetic, geometry, music, and astronomy.
and heard music as well as studied its theory. Though he disclaimed any expertise in composition or performance, music was extraordinarily important to him. His Harmony of the World (1619) sought to modernize Plato’s musical vision of the cosmos using the latest astronomical observations made by Tycho Brahe. In that book, Kepler used Tycho’s data to reconstruct the real songs of the planets and the kind of many-voiced musical polyphony (of which he thought the ancient Greeks ignorant) of their various individual songs (Figure 3). As an ardent Copernican, Kepler emphasized that now the Earth, no longer stationary, had a song like all the other planets. He calculated that the Earth’s song was a melancholy semitone, MI FA MI, endlessly
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Figure 3 n The planetary songs (including the moon) as calculated by Johannes Kepler in his Harmonices Mundi (1619), using the data of Tycho Brahe.
History of Astronomy | Music & Science
repeated, which he interpreted as singing “Miseria et Fames,” misery and famine. Living in a time of continual religious war and suffering himself persecution from both Catholics and Protestants, Kepler thought the Earth’s song was all too apt, all too accurately expressing (if not actually influencing) terrestrial misery. Kepler’s interest in music included familiarity with great composers of his time, especially Orlando di Lasso. Trying to understand the dissonant harmonies of the planets, Kepler invited the composers of his time to write a motet that would
Figure 4 n The opening measures of Orlando di Lasso’s motet “In me transierunt” as transcribed by Kepler and in a modern score.
show how those dissonances could be resolved. Several times he mentioned Lasso’s motet “In me transierunt,” whose opening notes (in then-current notation) were spelled MI FA MI (Figure 4). Thus, this composition could well have struck Kepler as a beautiful representation of the mournful song of the Earth. Kepler’s musical investigations led to an important astronomical discovery that became known as his third (or “harmonic”) law of planetary motion: the squares of the periods of any planet is proportional to the cube of its mean distance from the sun. Kepler announced this result with great excitement; since his youth he had been seeking such a deep relation connecting the orbits of different planets, but only Tycho’s precise observations allowed him to discover it. Kepler’s connection of squares and cubes (second and third powers) reminds us of the Pythagorean ratio for a fifth (3:2); he only discovered it in the course of looking for such musical ratios
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in different planetary data. Kepler’s harmonic law was of the greatest importance for Isaac Newton, who used it in his Principia (1687) to give a decisive argument for the inverse square law of gravitation. As an undergraduate, Newton himself had studied Boethius, the classic liberal arts musical text, on which he commented in detailed notes (Figure 5). In later life, he liked to remark that “Pythagoras’s Musick of the Spheres was gravity.” In experiments he began in early youth, Newton showed that white light was composed of a full spectrum of colors. He decided that spectrum spanned an octave in color, imposing the analogy of music onto light because he thought violet was a “recurrence” of deep red (he called it “purple”) in the same way that one D sounds akin to the D an octave higher. He took this analogy so seriously that he decided to name the colors in the spectrum in accord with the seven notes between one D and another (Figure 6). To make this work, Newton had to introduce into the spectral
Figure 5 n A page from Isaac Newton’s undergraduate notebook, dated November 1665, showing “ye distances of any two notes.” Courtesy of The Syndics of The Cambridge University Library.
colors orange and indigo to fill out a seven-note “keyboard” comprising Red Orange Yellow Green Blue Indigo Violet—the mnemonic ROY G BIV that everyone now learns as “the” colors in the spectrum. Many people find it difficult to differentiate orange from yellow or indigo from blue, and that’s
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Figure 6 n Newton’s illustration (1675) of the analogy between spectral colors and the seven notes of the diatonic scale. The note names follow the older nomenclature spelling the Dorian mode.
no accident: Newton inserted them to enforce his musical analogy while admitting that the colors in the spectrum are
somewhat arbitrary. But such remains the force of his authority that many people do not realize the curious musical backstory behind these colors. The note names follow the older
a
nomenclature spelling the Dorian mode. That story has a curious epilogue. In his later work on the colors seen when lenses are pressed together—“Newton’s rings”—Newton realized that the color spectrum did not really span an octave (2:1) but more nearly 9:14, about major sixth, like the interval between D and the B above it (Figure 7). He tried to explain this discrepancy away, curiously enough by using an argument that involved square and cubes in a way reminiscent of Kepler’s harmonic law of planetary motion. But though Newton obviously recognized a problem, he never went back to revise his views on the octave he had imposed on the spectrum since his earliest work. If he had, he might have found crucial evidence that would demonstrate the wave theory of light rather than the particle theory that Newton general-
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Figure 7 n Newton’s rings: (a) a modern recreation of his experiment using two plano-convex lenses pressed against each other, showing the characteristic moiré pattern; (b) Newton’s diagrams of the rings from his Opticks (1704).
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b
History of Astronomy | Music & Science
ly maintained. Had he cared to look, that ratio of a major sixth could have told him the ratio of the wavelengths of red to violet light (400:700 nanometers, in modern units). Though Newton took music seriously, perhaps he did not take it seriously enough. If he had, he might have advanced the wave theory of light a century; as it was, only in about 1800 did Thomas Young give definitive evidence for that theory, during which he commented upon Newton’s mistake (which Leonhard Euler had also noticed earlier). For my final historical example, let me leap forward another century to Max Planck, who first introduced the quantum in 1900 and thereby began the most consequential shift in modern physics. Like many other German scientists, Planck was a Kulturträger—a “bearer of culture,” someone steeped in literature and especially music. Planck played the piano, conducted, composed, and even thought of becoming a professional musician. He studied physics particularly for its philosophical qualities and what he considered its “search for the absolute,” for universal laws of nature. As a young man, he spent a year in Berlin with Hermann von Helmholtz, himself an exemplary Kul-
Figure 8 n Hermann von Helmholtz, painted by Ludwig Knaus in 1881. The table shows both his opthalmoscope as well as acoustic instruments, such as the round resonator.
turträger who was both physician and physicist, a passionate musician who had written the great works on physiological optics and on acoustics (figure 8). Indeed, during Planck’s year with him (1877) Helmholtz published the fourth and final edition of his masterwork On the Sensations of Tone as a Physiological Basis for the Theory of Music. Planck surely spent many evenings at his mentor’s home enjoying their mutual passion for music. When Planck was called to Berlin as professor of physics (1893), he was tasked with studying a new Eitz harmonium that Helmholtz had ordered, an innovative instrument capable of dividing an octave into 104 parts (Figure 9), compared to the 12 of a standard keyboard. This assignment in itself shows how important music was to the work of the Berlin physics department in Planck’s time. Planck was fascinated by this harmonium; even its
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daunting keyboard he learned to play “with a little practice,” as he modestly put it. Using it, he could test out Helmholtz’s theories that “natural tuning”—based on simple whole-number ratios that were the heir to the Pythagorean intervals—was superior to “equal temperament,” then as now the standard by which pianos and organs were tuned using irrational numbers to equalize all 12 steps in the scale. Indeed, Helmholtz was passionate in his advocacy of natural temperament (now generally called “just intonation”). He invited great musicians such as Johannes Brahms and Joseph Joachim to his house to play his harmoniums for them and elicit their agreement that equal temperament had ruined music. Brahms, notoriously gruff, refused to agree and privately called Helmholtz “an enormous dilettante.” Helmholtz persevered despite such opposition; though he did not make much headway in his own time, now performances of older music try to use the historically correct temperaments, not just the equal temperament that only became widespread during the 19th century. Then too, unaccompanied vocal ensembles like barbershop quartets will approach “natural tuning” as they strive for particularly close harmony. Planck was fascinated by these ideas and decided to make an experimental test of Helmholtz’s pet idea. In fact, this was the only experiment Planck
Figure 9 n An Eitz harmonium, whose keyboard (below) could divide an octave into 104 parts. Courtesy Deutsches Museum.
ever performed; he was a theoretical physicist, one of the first to hold a position specifically in that field, as opposed to the mixture of experiment and theory that had previously been the norm. Planck decided to write short compositions to test whether “natural tun-
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ing” really was more natural than equal temperament. He constructed a four-part piece for unaccompanied voices so that if the singers really were tracking the “natural” intervals (not using a piano to enforce equal
Figure 10 n Max Planck’s first composition to test Helmholtz’s theory about singers’ preferences for “natural” versus equal tuning.
temperament), by the end of the piece the choir would have sunk down an entire half-step in pitch (figure 10). Fully expecting Helmholtz’s theory to be borne out in practice, Planck was quite surprised when the singers kept their original pitch steady, instead of dropping it as the “natural tuning” would have dictated. Following good experimental procedure, he also constructed another test piece in which the pitch should have risen a half-step if the singers were following “natural tuning”: again they stayed true to the piano, even though singing unaccompanied. Planck concluded that habit was stronger than “nature”: growing up hearing pianos play in equal temperament (and having choral directors insist on holding those pitches steady), the singers were influenced more by those long-established habits than by the presumably “natural”
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desire to sing in close harmony. Planck published these results in a musicological journal, though they long remained unknown because they were not included among his other scientific papers. One can only wonder what Helmholtz would have made of this startling contradiction to his cherished theory, but he had far worse problems: after a sudden fall, he died in 1894, “the black year of German physics” in which Planck’s colleagues Heinrich Hertz and August Kundt also died. As the sole surviving professor of physics in Berlin, Planck had to set aside his work on the harmonium and take up other projects. The German lighting industry was pressing for practical help to design optimal light bulbs, which involved investigating the laws of radiation by heated bodies that were studied experimentally in Berlin. Planck’s interest in finding absolute laws of nature, especially in relation to thermodynamics, led him to address these new experimental findings. His autobiography passes directly from his work on the harmonium to his work on black-body radiation and the quantum postulate Planck put forward to explain his colleagues’ experiments. Thinking back to the analogy between color and sound, one might say that Planck was trying to find the “natural tuning” that governed the spaces between the allowed colors of a heated body considered as if those shades were adjacent “keys” of a cosmic harmonium. Planck broke the spectrum of light from a heated body into equal steps according to his now-famous formula E = hν, where E is the energy of the light, ν its frequency, and h a
new constant of nature that essentially specified the size of the interval between the “keys.” As he told his son Erwin at the time, Planck felt that his discovery was momentous because he had found “natural units” of length and time that would hold throughout the universe and could be recognized by any species of intelligent beings. These natural units showed that light obeyed an absolute and “natural tuning” that was at the same time perfectly equal because of the equal energy steps between the keys: hν, 2hν, 3hν,
4hν . . . Though Planck did not explicitly draw attention to this correspon-
dence, it is hard to imagine that this perceptive man did not notice that his work managed to reconcile the natural with the equal in the realm of light, even though in the music he studied “natural tuning” was at odds with
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“equal temperament.” By telling the story of
a
the harmonium next to that of black-body radiation, Planck’s autobiography certainly invites us to consider their relation. The interaction between music and science continues to evolve in ways that show their close relation over many centuries. Today, particle physicists find what they call “resonances,” a term that directly reminds us of the resonant vibrations of bodies, going back all the way to the vibrating glasses already used by the Pythagoreans so long ago
b
(figure 11). I will close with the recent discovery of gravitational waves by the twin detectors of LIGO in Washington and Louisiana, each composed of 4 km long L-shaped vacuum tubes capable of registering minute vibrations (figure 12). On September 14, 2015, both detectors simultaneously registered the passage of vibrations that strongly indicated as their source two merging black holes about 1.3 billion light years distant. The signal was recorded as a “chirp” played around the world, a swooping glissando that came up to about middle C on the piano. As the LIGO team emphasized in its public announcements, their instruments were “blind,” not registering any form of light or radiation but rather “feeling” the vibrations caused in the fabric of spacetime by gravitational waves emanating from a far-distant source. Thus, though no sound traveled directly, the grav-
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Figure 11 n Two examples of resonance: (a) resonance of a wine glass at its natural frequency of 454.73 Hertz, plotting the amplitude of the glass’s motion versus the frequency of the sound exciting it; (b) resonance showing the detection by the ATLAS collaboration at CERN of Z neutral intermediate bosons (mass 90 GeV) by their decay into an electron-positron pair, plotting the number of detected events versus the invariant mass-energy of the observed electron-positron pair. Courtesy ATLAS collaboration.
History of Astronomy | Music & Science
itational waves were detected as vibrations and, in that metaphorical sense, were “heard” rather than “seen.” The constant description of these events
Figure 12 n The two LIGO gravitational wave interferometers at Livingston, LA (left), and Hanford, WA (right). Courtesy LIGO.
as “chirps” was a powerful reminder of the connection between vibrating bodies and the confirmation of Albert Einstein’s gravitational waves a century after he first proposed them. Even beyond this spectacular result, the ancient project to mathematize nature through the intermediacy of music continues to thrive. Arguably, modern science is for our civilization what the pyramids were for ancient Egypt or the cathedrals for medieval Europe: the great cultural project of the time. Compared to them, the “invisible pyramid” of modern science (as Loren Eiseley called it) is not a static artifact or construction but continues and develops with all the dynamism of music.
PA
About the Author Peter Pesic is director of the Science Institute and musician-in-residence at St. John’s College, Santa Fe. He is the author of Labyrinth: A Search for the Hidden Meaning of Science; Seeing Double: Shared Identities in Physics, Philosophy, and Literature; Abel’s Proof: An Essay on the Sources and Meaning of Mathematical Unsolvability; Sky in a Bottle; Music and the Making of Modern Science; and Polyphonic Minds: Music, Science, and Expression (to appear fall 2017).
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BUY
Experiencing Space
E
xcluding the nonprofessional astronauts/cosmonauts who were taken into space for political or business reasons over the years, space tourism got
off the ground in April 2001, when the American engi-
neer Dennis Tito traveled to the International Space Station for an eight-day trip. Between then and 2016, a total of seven people each paid tens of millions of dollars to travel up there. Indeed, Dr. Charles Simonyi had so much fun on his first trip that he went for a second flight.
By Neil F. Comins
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Image credit: Elijah McNeal
Experiencing Space | Space Tourism
S
ometimes called “commercial space travel,” the opportuni-
ties for tourists to go into space are about to skyrocket in the next few years. A variety of companies, some owned by countries, some by nongovernmental corporations, and some by entrepreneurs (and some in combinations), are developing all aspects of space flight, including launch vehicles, spacecraft, and habitats for visiting or living in space. Let’s consider some of the very real options for space travel in the coming decades. “Space” is commonly defined to begin about 100 km (62 mi) above the Earth’s surface. That boundary is called the Kármán line after the Hungarian-American engineer Dr. Theodore von Kármán (1881–1963), who did a very interesting calculation related to airplanes and satellites. Kármán knew that the higher you go, the lower the air density (which is why people who go from low-lying communities, like Washington, DC, to places in the mountains, like Denver, Colorado, are often short of breath and have to learn to adapt to living at altitude). The lower air density means that the higher aircraft fly, the less lift their wings experience. Kármán asked and answered the question, “At what altitude would an airplane have to be flying so fast to keep itself aloft
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that its speed would be the same speed as a satellite (with no engine pushing it) orbiting at that same altitude?” The answer is about 100 km. If you don’t need engines to keep you up, then you are in space. There are four likely options for commercial spaceflight in the next two decades: suborbital flights, orbital flights, flights around the Moon that don’t land, and flights to the surface of the Moon. It is likely that all tourist spacecraft launched from Earth will have wings that will enable them to glide to a landing back on Earth. Some of these vehicles will have on-board rockets, some will be strapped to rockets, and some will use both rocket sources. Let’s briefly consider each of these four space travel opportunities. First, a suborbital flight will be a powered ascent that crosses the Kármán line. These vehicles are designed to use up virtually all their fuel on the way up. After the engine stops firing, the space vehicle will begin slowing down while continuing upward in an arc that eventually levels off and then begins descending earthward. The path will be similar to the path of a baseball hit toward the bleachers. On this journey you will go into space but not into orbit around the Earth. For about six minutes at the
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top of your trajectory you will be weightless, during which time you will be able to see nearly half of the Earth at once, float around the cabin, and possibly join the 62-mile-high club. Once you start descending, you will feel your weight return, and you will have to return to your seats for the remainder of the trip, which will be a controlled glide back to Earth. While suborbital flights will require some training, all the other spaceflights in the near future will probably
require
months of preparation. The second space flight opportunity is going to be travel to low Earth orbit, where either you will spend several days or more in the spacecraft that brought you up there or, more likely, in an orbiting space station. Low Earth orbit space stations, like the International Space Station, orbit much higher than the Kรกrmรกn line to prevent air friction from the very thin air at that altitude causing the space station to lose energy and spiral earthward. Your trip will be in two stages; first, a high-speed rocket flight to orbit just above the Kรกrmรกn line and then a more leisurely spiral out to your destination. This is more economical than flying straight to your final destination. Once at your destination, you will
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have a few days of uncomfortable adjustment to prolonged weightlessness, and then the fun begins. Besides experimenting with weightlessness, one thing that most astronauts spend a lot of time doing is looking at the Earth. Since a low Earth orbit takes about 90 minutes, in half an orbit you can see stunning views of both the daylight and nighttime sides of the Earth, which appear profoundly different from each other and from anything you can see from here on Earth. Often you will be able to see aurorae sweeping around one or both of the Earth’s poles. You will find that your sense of taste, among other things, will be very different than it is on Earth. Things tend to taste blander in space, which is why your travel company will provide spicier foods than those that you have here on Earth. An experience worth considering is going for a “spacewalk” outside your station. Indeed, spacewalks will likely be optional (spelled “additional cost”) opportunities for this trip and all the trips to the Moon. The third option for spaceflights in the very near future will be round-trip journeys to the Moon but without landing. There are a variety of paths your spacecraft can
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take to get you there. In any case, like the Apollo astronauts, you will first rocket into orbit around the Earth. You may stay there or in an orbiting space station until you adjust to weightlessness. When flights to the Moon become a serious industry, it is very likely that the spacecraft taking you into orbit and to an orbiting space station will not be the one taking you to the Moon. Instead, you will board a “shuttle” for that purpose. This process is much more efficient in terms of fuel and technology, but it is probably several decades down the road. In any event, once in your translunar spacecraft, a rocket attached to it will ignite, taking you via one of a variety of possible routes there. Some trips are more costly in fuel but take less time than the more fuel-efficient
routes.
(Although your spacecraft will have wings, they will be useless in the space.) With present technologies, it takes about three days to get to the Moon. During that time, you will be weightless and able to enjoy the flight by watching Earth and the Moon and doing things in zero gravity. Upon approaching the Moon, rockets will fire and slow your spacecraft, so that the Moon’s gravitational attraction can grab you and whip
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you around its far side. Since that side never faces the Earth, you will be one of the few humans to ever see it directly. The best place to see the details on the Moon, by the way, is on the boundary between day and night there, where the shadows are longest. This is called the terminator. The return to Earth will be a reverse of the trip out, also taking about three days. Unless you are traveling via shuttle, your
spacecraft
will
decelerate
near Earth and spiral down until the air catches the wings of your spacecraft, and you soar down to an airplane-like landing. The final trip that will be available in the next few decades will likely be trips to the surface of the Moon. Like the Apollo lander, you will probably descend in a shuttle rocket that stays on the Moon while your spacecraft from Earth orbits the Moon. Because the Moon has a lower mass and a lower average density than the Earth, its surface gravity is only about 17% as strong as we feel on Earth. As a result, you will weigh less than 1/5 as much there as you do today. One of the many things you will have trained for is walking and getting up when you fall in low gravity. Among the activities you can do
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on the surface are hiking and traveling to interesting features, including craters, hills, rock formations, cliffs (called scarps), possibly caves, and, depending on where you land, one of the Apollo landing sites. These sites are likely to be protected as international monuments. Returning to lunar orbit and to your spacecraft, you will fly home as described above for flights around the Moon. Every aspect of the preparation for space travel and the experiences in space is filled with challenges and opportunities, most of which are unlike any you will ever experience on Earth. You can learn much more about the space travel experience, as well as other upcoming space travel opportunities, in the book The Traveler’s Guide to Space: for One-Way Settlers and Round-Trip Tourists.
PA
Space travel poster images courtesy of NASA. Click on the icon or go to www.jpl.nasa.gov/visions-of-the-future to enjoy the full set of creative posters.
About the Author Astronomer and former NASA/ASEE scientist Neil F. Comins is professor of physics and astronomy at the University of Maine. His new book, The Traveler’s Guide to Space, is the go-to resource for anyone interested in space exploration. His other titles include Discovering the Universe, 10th edition (2014), What If the Earth Had Two Moons? (2010), Heavenly Errors: Misconceptions about the Real Nature of the Universe (Columbia, 2003), and What If the Moon Didn’t Exist? (1993).
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It’s resolution is just beautiful-running at 16 megapixels, it nearly doubles the resolution of camera’s nearly twice it’s cost Wide range of cameras that cover all facets of astrophotography Has a powerful two stage TEC cooling system that is capable of cooling of up to 45 degrees below the ambient temperature. OC
•
SE
LL
TELES
Community
I recently checked out a telescope at my local library. Wait, what? Yes, you read that correctly. In addition to books, movies, music, and online resources, my local library system checks out telescopes.
Check It Out! A Blueprint for a Library Program in Astronomy
BY JOHN FOSSETT
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Community | Check It Out
T
he telescope came in a kit with all the basics to get you started gazing at the night sky. It was very simple to set up; it took me about 10 minutes from the time I pulled into my driveway
until I had the telescope set up in the backyard—and that’s without prior experience using the items in the kit. I was able to see the moons of Jupiter, get a better look at the “Horse and Rider” double star in Big Dipper’s handle, and check out some phenomenal views of the moon. Approximately three years ago a couple of members of our local astronomy group approached me with an idea about the library lending telescopes. They read an article about the New Hampshire Astronomical Society (NHASTRO, http://nhastro.com/ltp.php) and the 100 or so libraries they inspired and supported to get telescope kits to loan to their patrons. The program has been a huge success. Our local astronomers proposed that we acquire two to three telescopes and assemble them in a padded tote with a star finder and some astronomy books. I was intrigued. We set a date for the first of many meetings to determine how many kits to assemble, what type of telescope we wanted, what else we’d like to include in the kit, how to pay for the kits, how to maintain them, etc. I began my background research. I identified a dozen New Hampshire libraries which were comparable in size to our largest branches and contacted them with a list of questions about the telescope lending service. The librarians were quick to provide feedback, and all felt the kits were a great addition and a positive experience for patrons and staff. Armed with information from the public libraries already in the telescope business, I continued to move forward. Determining the type of telescope was the easiest part of the project. NHASTRO has a recommendation for a telescope (Orion StarBlast 4.5-inch Astronomical Telescope), and they provide instructions for modifying the
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instrument
so
that
it’s easier to use and maintain. Next up was a discussion about what to include with the telescope. That was a much longer conversation. We brainstormed for a bit to create the initial list and then reviewed it. We opted for a very basic kit with just a few items (telescope, operator’s
manual,
The Stars by H.A. Rey, a Miller Planisphere starfinder, and a red flashlight to preserve night vision). Limiting the kits to a few basic
items
proved
cheaper for us, not to mention easier for library users. We’re fortunate to have two active astronomical organizations within the library’s service area, and both were happy to provide maintenance and support for the library’s telescope kits. I should add that when I spoke with the librarians in New Hampshire, nearly all shared that the Orion StarBlast telescope stood up to the rigors of institutional use (one librarian used the term “bulletproof”) and required very little maintenance. We decided on three kits to start with, thinking that we could add more if the service was successful. With the cost of the tote added to the price list for the rest of the kit’s contents we were estimating $300 per kit. If we asked for
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$1,000, that would give us enough for the three kits and leave a little for the cost of maintaining them. Next step: find a funding source. Some of the New Hampshire libraries were funded by their local astronomy groups, some were funded by their Friends of the Library groups, a few used library collection dollars to acquire their kits, and some just relied on donations. Funding was going to be our biggest challenge. We considered applying to grant sources on the national level, but we have a few local organizations providing grant funding to local nonprofits. Given the perceived competition on the national level, we opted for local funding and began preparing the grants. The president of one local astronomy group won an Orion StarBlast 4.5inch Astronomical Telescope in a raffle, which he donated to the cause, while the president of the other local astronomy group wrote the grants. The grantors were intrigued by the idea and asked if we’d do a presentation. I accompanied the astronomy group president, we presented, and they funded the project. Once we got the funds it took less than a week to acquire the kit’s contents. Another few days were needed to modify the telescopes according to NHASTRO specs, and the labeling and cataloging of the kits took another week. The entire process from initial meeting to the first checkout took approximately three years. Our project took considerably longer than other systems, but we wanted to be thorough, and we had to wait for the grant cycle. As I type there are 62 reservations on our three telescope kits, so now I’m looking into the possibility of securing funding for three more kits. Let me know if you’d like to contribute!
PA
About the Author John Fossett grew up in a sleepy little fishing village in northern New England. For two decades he worked in the maritime industry, eventually attaining the position of captain. In the late ’90s he enrolled in the library school at the University of Washington. He now works as a reference librarian at the Bainbridge Branch of the Kitsap Regional Library.
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Radio Astronomy
RADIO ASTRONOMY—HISTORY SETS THE STAGE
T
he field of radio astronomy owes a great debt to the famously failed Michelson–Morley experiment, which set out in 1887 to
characterize the effects of mysterious luminiferous “aether wind” on the speed of light. One of science’s more fruitful failures, it tilled the ground for Einstein’s special theory of relativity.
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Radio Astronomy | Galactic Quests
At the center of the experiment was Mi-
at the Parkes Observatory, northwest of
chelson’s ingenious invention, the inter-
Sydney, Australia, put it this way: “The
ferometer, the basic concept of which is
power received from a strong cosmic radio
still at work in modern radio telescope
source . . . is about a hundredth of a mil-
arrays—and still revealing, if not always
lionth of a millionth of a Watt (10-14 W). If
solving, the deep mysteries of the cosmos.
you wanted to heat water with this power
Interferometry allows radio astron-
it would take about 70,000 years to heat
omers to not only amplify distant sig-
one drop by one degree Celsius.”
nals, but also to increase their resolution,
Consequently, the drive for high sensi-
providing ever greater degrees of detail
tivity (plus the additional challenge pre-
on otherwise murky phenomena. This is
sented by radio emissions’ long wave-
a great challenge, because radio waves
lengths) is why radio telescope antennas,
emanating from space are exceptionally
whether used singularly or in an array,
weak. So weak, in fact, that astronomers
require such large collecting areas. The
The Michelson interferometer continues to be used in many scientific experiments. It is well known for the famous Michelson-Morley experiment of 1887, which sought to measure the earth’s motion through the supposed luminiferous aether that most physicists at the time believed was the medium in which light waves propagated.
Arecibo radio telescope, for example, measures 305 meters across, whereas the ASKAP array, presently under construction in Western Australia, will ultimately be made up of 36 identical antennas, each measuring 12 meters in diameter, but comprising a single “distributed” instrument with a large effective collecting area. (To achieve the same sensitivity with a single dish, its area would have to be approximately one square kilometer—a diameter of about 1.1 km!) These arrays rely upon “aperture synthesis,” a type of interferometry, to combine the signals from the individual antennas to yield resolution equivalent to
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that of a telescope of diameter equal to
could detect radio waves from the cen-
the greatest distance between its individ-
ter of the galaxy—well beyond the range
ual elements.
of optical instruments—the era of the
R
•••
adio astronomy had its formal genesis
it, the discovery of a great many mys-
in 1931 when Karl Jansky of Bell Labs
terious phenomena—not the least of
began the search for the source of radio
which is the Milky Way’s black hole that
noise that was feared might cause inter-
Jansky unwittingly exposed in his 1931
ference with Bell’s transatlantic com-
RFI experiment!
munications system. With the help of a
Jesse Greenstein, another astronomer
large antenna he constructed, he found
who recognized the importance of Jan-
it. It turned out to be near the center of
sky’s findings at the time, noted that
the Milky Way (in the constellation Sag-
analysis of radio waves emanating from
ittarius), its extraterrestrial nature causing a bit of a stir. As there was nothing to be done about such “star noise,” Jansky’s bid to investigate the phenomenon further was rejected, and he moved on to other projects at Bell. But Grote Reber, an amateur radio
operator
who
learned of Jansky’s discovery,
picked
up
Jansky
where
left off, building a 9.5-meter parabolic dish antenna in his back yard. With it, he compiled the first survey of the radio sky, which he completed in 1941. When
astronomers
realized
that
the
new radio telescope
136
great radio telescopes began. And with
popularastronomy.com | Fall 2017
Jansky, pictured with his seminal radio antenna tuned to receive radio waves at a frequency of 20.5 MHz. It had a diameter of approximately 100 ft. and stood 20 ft. tall. By rotating the antenna on a set of four Ford Model-T tires, it could pinpoint the location of a received signal.
Radio Astronomy | Galactic Quests
space provided researchers with “10,000
explored: one-off transient radio bursts
times the information” they could get
whose duration is measured in milli-
from optical astronomy. This would, in-
seconds and are presently of unknown
deed, revolutionize our understanding of
origin—events
the cosmos.
than Michelson’s luminiferous aether,
far
more
mysterious
The next big discovery in the field
and even rarer. In fact, only a handful
came on November 28, 1967. Jocelyn
of such transients have been recorded to
Bell Burnell and Antony Hewish ob-
date. But that’s about to change.
served pulses separated by 1.33 seconds that originated from a fixed location. The pulses followed sidereal time, ruling out man-made radio frequency interference. And when observations with another telescope confirmed the event,
137
RADIO ASTRONOMY ENTERS NEW COMPUTATIONAL ERA
D
r. Nathan Clarke, a research engineer with the International Centre for Ra-
dio Astronomy Research at Curtin Uni-
it eliminated anything intrinsic to the
versity in Perth, led the development
telescope itself. It was, indeed, a great
of a novel transient detection engine
mystery. Burnell recalled, “We did not
(dubbed Tardis) that captures and pro-
really believe that we had picked up sig-
cesses these fleeting signals in real time
nals from another civilization, but ob-
from the multiple beams of a telescope
viously the idea had crossed our minds,
array. It’s no small challenge; doing
and we had no proof that it was an en-
so involves a series of computational-
tirely natural radio emission. It is an
ly intensive operations that begins with
interesting problem—if one thinks one
“cleaning up” the faint, noise-shroud-
may have detected life elsewhere in the
ed signals so that the evanescent events
universe, how does one announce the
can be detected at all.
results responsibly?” With tongue in
Unlike Michelson’s spurious “aether
cheek, they dubbed the signal LGM-1,
wind,” the very real “interstellar fog”
for “little green men.”
has a decided effect on the propagation
Radio astronomers would continue to
of electromagnetic waves. Narrow pulses,
discover myriad new sources of radio
whether emanating from a known pulsar
emissions, as well as reveal the cosmic
or ambiguous fast transient, are delayed,
microwave background radiation. And
dispersed, and scattered by free elec-
now, through the work of researchers at
trons in the ionized intergalactic soup,
Australia’s Curtin University, an entire-
reducing their detectability. The silver
ly new class of radio phenomena is being
lining in this cosmic cloud is that there
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Radio Astronomy | Galactic Quests
is information in those effects: low-
important data about the source and dis-
er-frequency radio waves travel through
tance of the event, as well as providing
the medium at a slower rate (and con-
new insights into the interstellar medi-
sequently are more dispersed) than the
um itself.
higher-frequency
wave
components.
“Fortunately,” Clarke explains, “there
The resulting delay in the arrival of the
are several methods to partially or com-
pulse at a range of frequencies provides
pletely remove dispersion, a process
the “dispersion measure” (DM), yielding
referred to as de-dispersion.” Clarke’s
Goldstone Observatory. Courtesy NASA/JPL-Caltech
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team ultimately settled on the incoherent
Radio Astronomy | Galactic Quests
de-dispersion variant, which operates
ASKAP system, for example, will perform
on the dynamic spectrum of each signal,
448 such trials simultaneously on each of
measured over successive short inter-
its 36 beams, producing a total of 16,128
vals of time. “The dynamic spectrum is
de-dispersed data streams, with trials
obtained by using a filter to separate the
distributed across a sufficiently granular
signal into many frequency channels and
DM range to minimize S/N attenuation
then squaring each channel’s signal and
between them. Each de-dispersed stream
integrating it over the desired measuring
is then searched for events matching the
interval. De-dispersion is then accom-
fast transient profile.
plished by applying delays to each chan-
Such massively parallel, computation-
nel to compensate for dispersion and
ally intensive operations are well beyond
summing the time-realigned channels.”
the processing capabilities of many-core
The result? A nice, clean pulse.
CPU-based computing systems; they are
But Clarke went further with the al-
simply unable to keep up with the enor-
gorithm, summing individual spectral
mous volume of data streaming continu-
samples across both frequency and time,
ously in real time. And yet this is exactly
providing a signal-to-noise performance
the demand that fast transient detection
advantage over other de-dispersers that
places upon a computational system.
sum only across frequency. He also struc-
The routine de-dispersion of pulsar sig-
tured the algorithm for greater scalability
nals, for example, never presented such
so that a larger number of beams can be
a challenge. “In fact,” Clarke explains,
de-dispersed simultaneously, making for
“the de-dispersion of pulsars has, up till
more efficient surveys of the skies.
recently, been done in software. That’s because the pulsar is always on; it’s pro-
TACKLING A TOUGH COMPUTE-INTENSIVE CHALLENGE
B
139
ducing regular radio impulses. You can record your data, take it away, and search for the pulses on your own time; you can
ecause the DM is unknown—and can
fold the signal over at the pulse period to
vary over a wide range of possibili-
get better sensitivity detection. But with
ties—determining the actual DM for a
fast transients, you can’t do any of that;
potentially detected pulse (with reason-
these are one-off events with no peri-
able accuracy and hence good signal-to-
odicity or predictability at all. And that
noise ratio) requires a large number of
is what has driven the need for radical-
parallel processes, each de-dispersing
ly accelerating the de-dispersion algo-
the signal for a particular “trial” DM. The
rithm. Fast transients, because they are
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Radio Astronomy | Galactic Quests
so irregular, fleeting, and weak, must be
hand, provides better performance over
detected and de-dispersed in real time.”
GPUs—and without the power penalty. “One of our motivations for using FP-
POWER CONSIDERATIONS
GAs” Clarke says, “is the need for sys-
To this end, some fast transient detec-
tems that are very power-efficient. FP-
tion pipelines have used graphics pro-
GAs have a factor of 10 improvement
cessing units (GPUs), as they are power-
in power over GPUs. That’s important,
ful enough to allow real-time searching
because these large radio telescopes are
over a large parameter space. However,
going to be with us for many decades,
they have also proven to be impractical
and there will be a great many FPGAs
due to their exceptionally high power
operating in the background, processing
consumption. Field-programmable gate
massive amounts of data. So the cost of
array (FPGA) technology, on the other
development will fade into insignificance
ASKAP is developing and proving technologies for the international Square Kilometre Array (SKA) telescope, which will start construction in Australia and South Africa in 2018. Credit: CSIRO
when you consider a system that will be running continuously for a very long period of time. The extra bit of effort up front pays off in huge power savings.” The development team, working cooperatively with JPL, selected Pico Computing to provide the FPGA-based high-performance computing platform (see the
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Radio Astronomy | Galactic Quests
sidebar at the end, Inside the Fast Transient
“Most of the design was captured in Ver-
Detection System). In addition to the pow-
ilog,” Clarke says, “and we parameter-
er savings, there other motivating factors
ized the key variables so that we could
driving the choice of an FPGA-based sys-
switch to a new variant very quickly. We
tem, most notably its simple scalability
pretty much just change parameters to
and ease of reconfiguration.
suit the telescope, recompile, and load the new bitfile into the FPGAs.”
MEETING THE TWIN CHALLENGES OF SCALABILITY AND FLEXIBILITY Because of its parallel architecture, the performance of the fast transient detector scales linearly with the number of FPGAs in the system. In the case of the ASKAP array, with up to 36 beams in its beamformer, Clarke was able to accommodate nine beams in each FPGA of the six-FPGA Tardis system, yielding a compact and economical solution comprising a single PCIe board. Equally important was the ease of reconfiguring the Tardis board for operation with different radio telescopes. This need became manifest when the scope of the ASKAP array development effort was scaled back, delaying the interface that had been planned for the transient detection system. “Unfortunately,” Clarke added, “that meant we’d have to try out our system on other telescopes.” The good news was that reconfiguring the Pico Computing-based Tardis system for different antennas was straightforward, requiring only the modification of the parameters needed to adapt to the new telescope.
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Pico Computing’s high-performance computing modules integrate a Xilinx UltraScale FPGA and Micron’s high-bandwidth Hybrid Memory Cube. Up to six of the business card-sized modules snap onto any of Pico Computing’s PCIe backplanes (with up to eight backplanes in a 4U rack), filling a single PCIe slot with considerable parallel processing density for compute-intensive applications.
Radio Astronomy | Galactic Quests
The most important of these parame-
at the Goldstone Observatory, part of
ters is the SST (sample selection table),
the Goldstone Deep Space Communica-
into which the user loads a set of pre-cal-
tions Complex in the Mojave Desert, and
culated dispersion profiles tailored to the
operated for JPL. The 34-meter diame-
observing frequency of the telescope and
ter single-dish antenna (dubbed DSS-13
the range of DMs to be searched. Other
“Venus” experimental station), unlike
parameters include the antenna’s field of
the 36-beam ASKAP, has no need for
view, minimum sensitivity, angular sen-
summing signals across multiple anten-
sitivity, integration time, number of fre-
nas, thus freeing all six of the system’s
quency channels, beams per FPGA, and
FPGAs to be used for de-dispersion.
other configuration details. The first opportunity for reconfigura-
beams and 1,024 DMs and is deployed at
tion was the deployment of the system
the Murchison Widefield Array (MWA) in
The Murchison Widefield Array (MWA) is a low-frequency radio telescope operating between 80 and 300 MHz. It is located at the Murchison Radio-astronomy Observatory (MRO) in Western Australia, the planned site of the future Square Kilometre Array (SKA) lowband telescope, and is one of three telescopes designated as a precursor for the SKA. Credit: Pete Wheeler, the International Centre for Radio Astronomy Research.
142
A third variant processes up to six
popularastronomy.com | Fall 2017
Western Australia—a low-frequency radio array operating in the 80–300 MHz range. Clarke expects to see much more dispersion
at
those
lower
frequen-
cies, which necessitated the increase in de-dispersion trials. “In the original ASKAP version,” Clarke explains, “we could support many separate beams si-
Radio Astronomy | Galactic Quests
multaneously in one FPGA, de-disperse
their extraterrestrial origin, chalking
them, and search for these fast tran-
the phenomenon up to artifacts of the
sients. But the MWA required many more
telescope itself. But recent detections
de-dispersion trials and frequency chan-
of similar signals with other telescopes,
nels to detect the pulses. Consequently,
most notably at Arecibo, have add-
we could only fit a single beam into an
ed weight to their existence and have
FPGA.” The advantage, though, is MWA’s
ignited efforts to determine what is
exceptionally large field-of-view, which
causing them. And with new, real-time
lends itself well to intercepting isolated,
instruments emerging to capture the
short-duration pulses.
events in large numbers, astronomers
I
•••
can begin to study and characterize
f the dispersion measures associated
them more rigorously, solving the next
with the fast transients are to be be-
great cosmic mystery. Clarke, however,
lieved, then these exotic events origi-
still looks forward to the full realization
nate from sources billions of light years
of the ASKAP array, as it will capture
away, well beyond our galaxy. Since the
radio signals with unprecedented sen-
first such transient was detected in 2007
sitivity over large areas of sky. With a
at the Parkes Observatory’s 64-me-
wide instantaneous field-of-view, the
ter telescope in Australia, these mys-
ASKAP/Tardis combination will be able
terious events have captured astron-
to survey the whole sky vastly fast-
omers’ imaginations. In fact, they are
er than is possible with existing radio
so strange that many initially doubted
telescopes.
PA
INSIDE THE FAST TRANSIENT DETECTION SYSTEM
O
riginally designed for the ASKAP array, the Tardis fast transient detection system consists of a host computer equipped with a commercial FPGA platform provided by Pico Computing. The computer receives dynamic power spectra from all antennas via a dual 10-GbE network interface card (NIC). The FPGA platform consists of a Pico Computing PCI Express board supporting an array of up to six Pico Computing FPGA plug-in modules. The board connects to the host through a PCIe expansion slot and provides an 8-lane PCIe fabric interconnecting the FPGA modules. One FPGA is used to combine beams
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Radio Astronomy | Galactic Quests
across antennas and polarizations, and four FPGAs implement the de-dispersion and transient detection functions, with each processing nine of the 36 combined beams. The summing FPGA delivers combined beam data to each of the other FPGAs using a daisy-chain interconnection. Software running on the host CPU is mainly responsible for managerial tasks, such as communicating with the telescope control system to obtain relevant operational parameters, and configuring and initializing the FPGAs. The host software can also record the de-dispersed time series to disks. For each tentative pulse detection, a capture trigger signal is generated by the software and sent to all beamformer assemblies. The saved voltage samples can then be downloaded from the beamformer assemblies via the same Ethernet switches and recorded to disk. “The Pico Computing hardware accelerator is a very good platform,” Clarke adds. “It was smooth going getting it up and running.” For more information on the Tardis system, see “A Multi-beam Radio Transient Detector with real-time De-dispersion over a Wide DM Range,” Journal of Astronomical Instrumentation, Vol. 3, no. 1, 2014.
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Astrophysics
Einstein’s Castle in the Air
W
hen I first learned about nonlocality as a graduate student in the early 1990s, it wasn’t from my quantum-mechanics professor: he didn’t see fit to so much as
mention it. Browsing a local bookshop, I picked up a newly published book, The Conscious Universe, which startled me with its claim that “no previous discovery has posed more challenges to our sense of everyday reality” than nonlocality. The
By George Musser 146
popularastronomy.com | Fall 2017
phenomenon had the taste of forbidden fruit.
Astrophysics | Nonlocality
In everyday speech, “locality” is a slightly pretentious word for a neighborhood, town, or other place. But its original meaning, dating to the 17th century, is about the very concept of “place.” It means that everything has a place. You can always point to an object and say,
‘‘
In a famous essay in 1936, Einstein wrote that the most incomprehensible thing about the universe is that it is comprehensible. At first glance, this statement itself seems incomprehensible. The universe is not a conspicuously rational place.
“Here it is.” If you can’t, that thing must not really exist. If your teacher asks where your homework is and you say it isn’t anywhere, you have some explaining to do. The world we experience possesses all the qualities of locality. We have a strong sense of place and of the relations among places. We feel the pain of separation from those we love and the impotence of being too far away from something we want to affect. And yet quantum mechanics and other branches of physics now suggest that, at a deeper level, there may be no such thing
’’
as place and no such thing as distance. Physics experiments can bind the fate of two particles together, so that they behave like a pair of magic coins: If you flip them, each will land on heads or tails—but always on the same side as its partner. They act in a coordinated way even though no force passes through the space between them. Those particles might zip off to opposite sides of the universe, and still they act in unison. These particles violate locality. They transcend space. Evidently, nature has struck a peculiar and delicate balance: Under most circumstances it obeys locality, and it must obey locality if we are to exist, yet it drops hints of being nonlocal at its foundations. That tension is what I explore in the book Spooky Action at a Distance. For those who study it, nonlocality is the mother of all physics riddles, implicated in a broad cross section of the mysteries that physicists confront these days: not just the weirdness of quantum particles, but also the fate of black holes, the origin of the cosmos, and the essential unity of nature. For Albert Einstein, locality was one aspect of a broader philosophical puzzle: Why are we humans able to do science at all? Why
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BUY
Astrophysics | Nonlocality
is the world such that we can make sense of it? In a famous essay in 1936, Einstein wrote that the most incomprehensible thing about the universe is that it is comprehensible. At first glance, this statement itself seems incomprehensible. The universe is not a conspicuously rational place. It is wild and capricious, full of misdirection and arbitrariness, injustice and misfortune. Much of what happens defies reason (especially when romance or driving is involved). Yet against this backdrop of inexplicable happenings, the world’s rules glow with reassuring regularity. The sun rises in the east. Things fall when you drop them. After the rain comes a rainbow. People go into physics out of a conviction that these are not just gratifying exceptions to the anarchy of life, but glimpses of an underlying order. Einstein’s point was that physicists really had no right to expect that. The world needn’t have been orderly at all. It didn’t have to abide by laws; under other circumstances, it might have been anarchic all the way down. When a friend wrote to ask Einstein what he’d meant by the comprehensibility remark, he wrote back, “A priori one should expect a chaotic world which cannot be grasped by the mind in any way.” Although Einstein said comprehensibility was a “miracle” we shall never understand, that didn’t stop him from trying. He spent
‘‘
his entire professional life articulating exactly what it is about the universe that makes it make sense, and his thinking set the course of modern physics. He recognized, for example, that the inner
Relativity theory says that no material thing can move faster than light. Without such an ultimate speed limit, objects might move infinitely fast, and distance would lose its meaning.
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workings of nature are highly symmetrical, looking the same if you view the world from a different angle. Symmetry brings order to the bewildering zoo of particles that physicists have found; entire species of particles are, in a sense, mirror images of one another. But among all the properties of the world that give us hope for understanding it, Einstein kept coming back to locality as the most important.
Astrophysics | Nonlocality
Locality is a subtle concept that can mean different things to different people. For Einstein, it had two aspects. The first he called “separability,” which says that you can separate any two objects or parts of an object and consider each on its own, at least in principle. You can take your dining chairs and put each one in a different corner of the room. They will not cease to exist or lose any of their features—size, style, cushiness. The entire dining-room set derives its properties from the chairs that make it up; if each chair can seat one person, a set of four chairs can seat four people. The whole is the sum of its parts. The second aspect that Einstein identified is known as “local action,” which says that objects interact only by banging into one another or recruiting some middleman to bridge the gap between them. Whenever a distance separates us from someone, we know we cannot have any effect on that person unless we cross the distance and touch, talk to, punch—somehow, make direct contact with—that person, or send someone or something to do it for us. Modern technology does not evade this principle; it merely recruits new intermediaries. A phone translates sound waves into electrical signals or radio waves that travel through wires or open space and then get translated back into sound on the other end. At every step of the way, something has to make direct contact with something else. If there is even a hairline crack in the wire, the message gets as far as a scream on an airless moon. Simply put, separability defines what objects are, and local action dictates what they do. Einstein captured these principles in his theory of relativity. Specifically, relativity theory says that no material thing can move faster than light. Without such an ultimate speed limit, objects might move infinitely fast, and distance would lose its meaning. All the forces of nature must wend their way laboriously through space, rather than leap across it in a single bound, as physicists used to suppose. Relativity theory thereby provides a measure of isolation among separated objects and ensures their mutual distinctness. Depending on your frame of mind, relativity theory and the
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Astrophysics | Nonlocality
‘‘
other laws of physics are either a satisfying deep order to the universe or a series of killjoy rules, like
In a world without locality, objects outside your body could reach inside without having to pass through your skin, and your body would lose its ability to control its internal condition. You would blend into your environment. And that is the very def inition of death.
’’
an authoritarian parent trying to take all the fun out of life. How great it would be to flap our arms and fly—but sorry, no can do. We could solve the world’s problems by creating energy—oh, physics won’t allow that, either; we can only convert one form of energy into another. And now comes locality, yet another draconian diktat, to spoil our dreams of faster-than-light starships and psychic powers. Locality dashes sports fans’ eternal hope that, by crossing their fingers or bellowing some insightful comment from their armchairs, they might give their team an edge on the playing field. Unfortunately, if your
team is losing and you’re serious about wanting to help,
you’ll have to get up and go to the stadium. Yet locality is for our own good. It grounds our sense of self, our
confidence that our thoughts and feelings are our own. With all due respect to John Donne, every man is an island, entire of himself. We are insulated from one another by seas of space, and we should be grateful for it. Were it not for locality, the world would be magical—and not in a happy, Disneyesque way. As much as sports fans may wish they could sway the game from their living rooms, they should be careful what they wish for, because supporters of the opposing team would presumably have this power, too. Millions of couch potatoes across the land would strain to give their side some advantage, making the game itself meaningless—a contest of fans’ wills rather than of talent on the field. Not just sports games, but the entire world would become hostile to us. In a world without locality, objects outside your body could reach inside without having to pass through your skin, and your body would lose its ability to control its internal condition. You would blend into your environment. And that is the very definition of death. By focusing on locality as a crucial prerequisite to comprehend-
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ing nature, Einstein crystallized 2,000 years of philosophical and scientific thought. For ancient Greek thinkers such as Aristotle and Democritus, locality made rational explanation possible. When objects can affect one another only by making direct contact, you can describe any event by giving a blow-by-blow account of “this hit that, which in turn knocked into that, which in turn bounced off some other thing.” Every effect has a cause linked to it by a chain of events unbroken in space and time. There’s no point at which you have to wave your hands and mumble,
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As painters have long realized, space is not mere absence, but a thing in its own right. What comes between objects on a canvas is as important to the composition as the objects themselves. For a physicist, space is the canvas of physical reality.
“Then a miracle occurs.” It wasn’t the miracle the Greek philosophers objected to—they weren’t atheists—so much as the mumbling. Even gods, they felt, should exert their power by clear and explicable rules. Locality is essential not just to the types of explanations that philosophers and scientists seek, but to the methods they use. They can isolate objects from one another, grasp them one at a time, and build up a picture of the world step by step. They are not faced with the impossible task of taking it in all at once. In 1948, toward the end of his life, Einstein summarized the importance of locality in a short essay: “The concepts of physics refer to a real external world . . . things that claim a ‘real existence’ independent of one another, insofar as these things ‘lie in different parts of space.’ Without such an assumption of the mutually independent existence . . . of spatially distant things, an assumption that originates in everyday thought, physical thought in the sense familiar to us would not be possible. Nor does one see how physical laws could be formulated and tested without such a clean separation.” Locality has such a pervasive importance because it is the essence of what space is. By “space” I don’t just mean “outer space,” the realm of astronauts and asteroids, but the space between us and all around us, the space that our bodies and everything else occupy, the space through which we swing a baseball bat or stretch a measuring tape. Whether you point your telescope at the planets
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or at the next-door neighbors, you are peering across space. For me, the beauty of the landscape comes from the giddy sense of spanning space, a sort of horizontal vertigo when you realize the little dots on the other side of a valley really are there and that you could touch them if only your arms were long enough. As painters have long realized, space is not mere absence, but a thing in its own right. What comes between objects on a canvas is as important to the composition as the objects themselves. For a physicist, space is the canvas of physical reality. Almost every attribute of our physical selves is spatial. We occupy a place. We have a shape. We move. Our bodies are intricate choreographies of cells and fluids dancing in space. Every interaction we have with the rest of the world passes through space. Living things are things, and what is a thing but a part of the universe that acquires an individual identity by virtue of occupying a certain volume of space? Physics is rooted in the study of how things move through space, and space defines practically every quantity that physics deals in: distance, size, shape, position, speed, direction. Other quantities of the world may not appear spatial, but are; color for example, corresponds to the size of a light wave. Only a very few properties of matter have no known spatial explanation, such as electric charge, and even these betray themselves by deflecting motion through space. When we look at an object, everything about it is ultimately spatial arising from how its particles are arranged; the particles themselves are the barest flecks. Function follows form. Even non-spatial concepts become spatial in physicists’ minds; time becomes an axis on a graph, and the laws of nature operate within abstract spaces of possibility. No less an authority than Immanuel Kant, whose ideas were a major influence on Einstein, thought it impossible to conceive of a world without space. What a twist of fate that the greatest champion of locality was also its undoer. Though best known to the wider world for relativity theory, Einstein actually won his Nobel for co-founding quantum mechanics, the theory that describes how atoms and subatomic particles behave. Actually, physicists think quantum
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mechanics describes how everything behaves, although its distinctive effects are strongest on tiny scales. The theory grew out of Einstein’s and his contemporaries’ epiphany that atoms and particles can’t just be little versions of the things we see around us. If they were—if they acted according to the classical laws of physics developed by Isaac Newton and others—the world would self-destruct. Atoms would implode; particles would explode; light bulbs would fry you with deadly radiation. The fact we’re still alive means that matter must be governed by some new set of laws. Einstein welcomed the strangeness; in fact, despite the reputation that he later acquired
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Physics is rooted in the study of how things move through space, and space def ines practically every quantity that physics deals in: distance, size, shape, position, speed, direction. Other quantities of the world may not appear spatial, but are; color for example, corresponds to the size of a light wave. Only a very few properties of matter have no known spatial explanation, such as electric charge, and even these betray themselves by def lecting motion through space.
as a rearguard defender of classical physics, he was consistently ahead of everyone else in appreciating the alien features of the quantum world. Among those features was nonlocality. Quantum mechanics pre-
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dicts that two particles can become blood brothers. For want of a mechanism to couple them, the particles should be complete-
ly autonomous, yet to touch one was to touch the other, as if the distance between them meant nothing. The scientific method of divide and conquer fails for them. The particles have joint properties that escape you if you view them one at a time; you must
measure the particles together. Our world is crisscrossed by a web of these seemingly mystical relationships. Atoms in your body retain a bond with everyone you have loved—which sounds romantic until you realize that you’re also linked to every weirdo who brushed against you while walking down the street. Particles on opposite sides of the universe can’t really be connected, can they? The idea struck Einstein as silly, a regression to pre-scientific notions of sorcery. Any theory that implied such “spooky actions at a distance,” he reasoned, had to be missing
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something. He figured that the world was in fact local and merely gave the impression of being nonlocal, and he sought a deeper theory that would lay bare the hidden mechanism whereby two particles can act in unison. Try as he might, though, Einstein could never find such a theory, and he recognized that he might be the one who was missing something. There might be no concealed clockwork. The principle of locality—and with it, our conception of space—might not hold. A few months before he died, Einstein reflected on what the dissolution of space might mean to our understanding of the world: “Then nothing will remain of my whole castle in the air including the theory of gravitation, but also nothing of contemporary physics.” What was really spooky was how sanguine most of his contemporaries were. To them, nonlocality was a nonissue. The reasons for their dismissive attitude were complicated and are still debated by historians, but perhaps the most charitable explanation is pragmatism. The questions that vexed Einstein just didn’t seem relevant to the practical applications of quantum theory. Only in
‘‘
the 1960s did a new generation of physicists and philosophers give Einstein’s worries a real hearing. The experiments they did suggested that nonlocality was not a theoretical curiosity, but a fact
Particles on opposite sides of the universe can’t really be connected, can they? The idea struck Einstein as silly, a regression to pre-scientific notions of sorcery. Any theory that implied such “spooky actions at a distance,” he reasoned, had to be missing something.
of life. And even then, most of their colleagues gave it little thought—which is why I practically had to stumble on the topic as a grad student. In the past 20 years, though, I’ve witnessed a remarkable evolution in attitudes. Nonlocality has surged into the currents of mainstream physics and swept far past the phenomenon that Einstein discovered. In my career as a science writer and editor, I have had the privilege of talking to scientists from a wide range of communities—people who study everything from subatomic particles to black holes to the grand structure of the cosmos. Over and over, I heard some variant of, “Well, it’s weird, and
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I wouldn’t have believed it if I hadn’t seen it for myself, but it looks like the world has just got to be nonlocal.” Researchers were like those matching particles on opposite sides of the universe, often not even knowing of one another, yet reaching the same conclusions. If Einstein thought nonlocality smacked of sorcery, does the new research lend credence to paranormal claims? Some have thought so. In past decades, a number of scientists speculated that nonlocal links between particles could endow you with psychic powers. For instance, if particles in your brain were entangled with particles in your friend’s, perhaps the two of you could communicate telepathically. At the other extreme, the supernatural intimations of nonlocality have been cause for many physicists to dismiss the whole area of research as hooey. In fact, there’s no connection. None of the evidence for ESP has ever stood up, and the types of nonlocal phenomena under discussion are too subtle to meld minds or sway distant baseball games. Some people are disappointed by that. They shouldn’t be. The real magic of the world is that it isn’t magical. For the reasons I discussed earlier, locality is a precondition for our existence. Any nonlocality must remain safely tucked away, emerging only under certain conditions, or else our universe would be inimical to life. What nonlocality gives us is much more impressive than any paranormal phenomenon: a window into the true nature of physical reality. If influences can leap across space as though it weren’t really there, the natural conclusion is: space isn’t really there. The Columbia University string theorist Brian Greene wrote in his 2003 book, The Fabric of the Cosmos, that nonlocal connections “show us, fundamentally, that space is not what we once thought it was.” Well, what is it, then? Investigating nonlocality may clue us in. Many physicists now think that space and time are doomed—not fundamental elements of nature, but products of some primeval condition of spacelessness. Space is like a rug with ragged edges and worn spots. Just as we can look at those frayed areas to see how the rug is woven, we can study nonlocal phenomena to
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‘‘ ’’
glimpse how space is assembled from spaceless components.
Over and over, I heard some variant of, “Well, it’s weird, and I wouldn’t have believed it if I hadn’t seen it for myself, but it looks like the world has just got to be nonlocal.”
“I always thought, and still do, that the discovery and proof of the nonlocality is the single most astonishing discovery of 20th-century physics,” says Tim Maudlin, a professor at New York University and one of the world’s leading philosophers of physics. In a paper in the late 1990s, he summed up the implications: “The world is not just a set of separately existing localized objects, externally related only by space
and time. Something deeper, and more mysterious,
knits together the fabric of the world. We have only just come to the moment in the development of physics that we can begin to contemplate what that might be.” At the same time, precisely because so much is at stake, other
scientists tell me nonlocality can’t be real—that one or another of the nonlocal phenomena will turn out to be a misinterpretation, and that it is a mistake to lump them together. Physicists have had enormous success with spatial reasoning and won’t give it up lightly. One skeptic, Bill Unruh, who is a physics professor at the University of British Columbia, feels much as Einstein did: “If I have to know everything about the universe to know anything, if we take nonlocality seriously, if what happens here depends on what the stars are doing, it makes physics virtually impossible. What makes physics possible is that the world is partitionable. If we really do have to look to the stars to see our future, then I don’t see how we can do physics anymore.” Apart from its inherent fascination, nonlocality is an ideal case study for scientific disputes. The disagreements between people such as Maudlin and Unruh are intellectually pure. No econom-
ic interests make you suspect ulterior motives. No lobbyists from ExxonMobil roam the halls. The adversaries have no overt personal animosity; many are friends. The mathematics is fairly simple; the experimental findings, undisputed. And still the debates drag
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on for generations. Today’s scholars rehearse arguments that go back to Einstein and those he sparred with in the 1920s and ’30s. Why is that? And what are the rest of us to do when the experts can’t agree? Consider the highest-profile scientific debate of recent times: climate change. Most climate scientists think human activity is warming the planet, some holdouts still disagree—and to someone reading a newspaper or surfing the web, the arguments can be baffling. Most people don’t have time to become experts in general circulation models or measurements of longwave radiation. But one thing we will see is that a debate can be resolved in a practical sense regardless of whether the experts go on arguing. In the case of climate change, the public already knows what it needs to. There’s a good chance of climate disaster and it’s only prudent to manage the risk, just as you don’t need a Ph.D. in combustion theory to know you should buy fire insurance for your home. Likewise, in the case of nonlocality, even the most die-hard skeptic now accepts that something very weird is going on, something that
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forces us to go beyond our deepest-held notions of space and time, something that we need to grasp if we are to know how the universe was born and how the natural world fits together in perfect unity. The social stories are not just a sideline to the science. They are directly pertinent, because in a fluid area of research, where ideas jostle and nothing is entirely clear, the conventional ways that people outside science assume it operates—through the application of fact, logic, equations, experiments—aren’t enough to bring closure. Scientists have to reach into gut feelings, metaphorical connections, and judgment calls about the adequacy of their basic principles. In deciding to explore nonlocality, I set off down what looked like a leisurely nature walk, but soon found myself
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Even the most die-hard skeptic now accepts that something very weird is going on, something that forces us to go beyond our deepest-held notions of space and time, something that we need to grasp if we are to know how the universe was born and how the natural world fits together in perfect unity.
Astrophysics | Nonlocality
entangled in an exotic rainforest filled with glistening leaves, labyrinthine byways, and tempting handholds swarming with fire ants. Some physicists thrill to the rebelliousness of questioning one of the oldest and deepest concepts in science. Others shudder at the madness. If locality fails, does it mean our universe is ultimately incomprehensible, as Einstein feared, or can physicists find some other way for it to make sense?
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About the Author George Musser is an award-winning journalist, a contributing editor for Scientific American, and the author of The Complete Idiot’s Guide to String Theory. He is the recipient of a Jonathan Eberhart Planetary Sciences Journalism Award from the American Astronomical Society and the 2011 American Institute of Physics Science Communication Award for Science Writing. He was a Knight Science Journalism fellow at MIT from 2014 to 2015. He has appeared on Today, CNN, NPR, the BBC, Al Jazeera, and other outlets. He lives in Glen Ridge, New Jersey, with his wife and daughter. This article is excerpted from his book, Spooky Action at a Distance: The Phenomenon That Reimagines Space and Time—and What It Means for Black Holes, the Big Bang, and Theories of Everything. Learn more at www.georgemusser.com.
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“Introduction: Einstein’s Castle in the Air” from SPOOKY ACTION AT A DISTANCE by George Musser. Copyright © 2015 by George Musser. Used by permission of Farrar, Straus and Giroux.
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Astrophotography
By Brenda Tharp
N
ight is the new day. Just take a look online at any popular photosharing site and you’ll see that the sky has become the new craze for many photographers. It appears that we’ve only just recently awakened to the fact that we have this amazing ceiling over our heads! PHOTO CREDITS This page: Elena Liseykina.
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All other pages: Brenda Tharp.
Astrophotography | Night Photography Photographing at night is a special part of what I do as a nature photographer. When I am out in the night in a remote area, I feel the Earth resting from the intensity of the sun; it is to me one of the most tranquil and peaceful times. And amidst all the calculations and careful setup for making a nighttime photograph, I don’t stop appreciating the beauty. I invite you to take a step outside, when you’re in a very dark area, and look up in amazement at the wondrous sight overhead. To experience the night while photographing it is simply awesome. Be ready to feel very small. My first exposures of stars were failed attempts. I was guessing, using film, and had to factor in reciprocity, and, well, I just wasn’t getting great
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results. But a few years later in Utah’s Canyonlands National Park, a very dark place, I made an eight-hour exposure, pointing south. When I awoke at 4:30 AM to close the shutter, it was 17 degrees Fahrenheit! Back home I had the film processed, and I finally had star trails, but they were mostly horizontal, and the film was green! The lab determined the green was likely due to the film freezing, as normal reciprocity shifts were red. And I didn’t have nice arcs in the star trails, because I had pointed south. It was an epic fail, and I had much to learn.
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Undaunted, I read more articles and tried again, this time with a digital camera. As star photography had become popular, there was more information about how to do it right, along with discussions about must-have lenses, motorized tracking
gear,
and
formu-
las for exposures. I was a bit overwhelmed. Did I really need tracking gear? I just wanted to make some images of the night sky when I was out camping and exploring. I knew if I was going to keep photographing stars, the process had to be easy to remember and apply without using a lot of technical gear. I started writing down formulas and laminating charts I made for what I wanted to do. It was exciting, and I discovered that you don’t have to be very technically inclined to get good results. You can certainly become more technical about your approach, and do things like multi-row panoramas, nine-hour exposure composites, or capture an eclipse, but the simple act of getting star trails or points of light is not difficult. With a chart as a reference tool and some notes,
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Preparing the Camera Nightgood Photography you can have success infor getting exposures Theresources checklist items for belowgetting are the same for and sharp stars. Many photography photogtechniques. Before much deeper into starsmost andnight moonlight
you get out in the dark, set up your camera raphy are available online and in books. This as follows: article will get you started in photographing during the night. Away we go, into the night! Use a fast lens, such as f/2.8, or f/1.4, with Bring caffeine, as you’re likely to need it. a lens hood (helps keep dew off the lens). Generally, use a focal length from 14–
Calculating Exposures28mm. for Star Photographs
Let’s assume you are working around the new Set your camera for RAW. moon, so moonlight isTurn not affecting your ex- (use off long-exposure noise reduction posures. Start by setting yourlater ISO software for to this).6400 with your aperture set to f/2.8 thenoise shutter Turn offand high-ISO reductionset (this only to 30 seconds. Focus on infinity affects JPEGs). just to have a Turn off any vibration-reduction features on your lenses and/or your camera. Switch to “Manual Focus” on the lens. Attach a programmable remote release to the camera (or a locking one). Use a smartphone to time your exposures if you don’t have a programmable release. Use a sturdy tripod. Have a rocket blower with you (helps keep dew off lens). Have extra batteries close at hand to switch out quickly if needed.
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relatively sharp picture, and make an exposure. Check
your
histogram.
The majority of the tonal values should fall within the first and third panels in from the left side, de-
Preparing the Camera for Night Photography The checklist items below are the same for most night photography techniques. Before you get out in the dark, set up your camera as follows: n
n
pending on whether you
n
have any light on the land
n
or if your subject/foreground is simply a silhou-
n
ette. If you need more exposure, increase your ISO until the exposure looks
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n
Use a fast lens, such as f/2.8 or f/1.4, with a lens hood (helps keep dew off the lens). Generally, use a focal length from 14–28mm. Set your camera for RAW. Turn off long-exposure noise reduction (use software later for this). Turn off high-ISO noise reduction (this only affects JPEGs). Turn off any vibration-reduction features on your lenses and/or your camera.
n n
n n
n
Switch to “Manual Focus” on the lens. Attach a programmable remote release to the camera (or a locking one). Use a smartphone to time your exposures if you don’t have a programmable release. Use a sturdy tripod. Have a rocket blower with you (helps keep dew off lens). Have extra batteries close at hand to switch out quickly if needed.
Astrophotography | Night Photography
good, as changing the aperture would affect how many stars show, and changing the shutter would affect the star movement. When you achieve a good exposure for the stars, you are ready to extrapolate settings that will work for your singular star trails
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and for the multiple, shorter exposures to be later composited.
PA
About the Author For over 28 years, Brenda Tharp has been photographing the world around her in response to the needs of creative professionals in the editorial and book publishing industries. Her award-winning images are in private collections across the country, and she provides finely crafted prints to interior decorators and corporations. Brenda specializes in creating strong compositions with an attention to light, color, form, and texture. She also creates story-telling photographs of people and places. Her images are widely used in ads, books, brochures, calendars, greeting cards, and magazines for a variety of clients, including National Geographic Books, Sunset, British Gas, Chronicle Books, Sierra Club Magazine, Nature Conservancy, Audubon, The Presidio Trust, National Park Service, and Michelin Travel Publications.
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This article is excerpted from Expressive Nature Photography: Design, Composition, and Color in Outdoor Imagery by Brenda Tharp, published by Monacelli Studio (an imprint of The Monacelli Press) on July 25, 2017.
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