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CELESTRON’S STARSENSE REVIEWED p. 62

www.Astronomy.com Vol. 42

GERALD RHEMANN: IMAGING COMETS AND NEBULAE p. 46

Journey inside globular cluster 47 Tucanae to see what astronomers would face under such a crowded sky.


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FROM THE EDITOR BY D AV I D J . E I C H E R

Editor David J. Eicher Art Director LuAnn Williams Belter EDITORIAL STAFF

Senior Editors Michael E. Bakich, Richard Talcott Production Editor Karri Ferron Associate Editors Liz Kruesi, Sarah Scoles Editorial Associate Valerie Penton

Rock with Starmus this September!

ART STAFF

Senior Graphic Designer Chuck Braasch Illustrator Roen Kelly Production Coordinator Jodi Jeranek CONTRIBUTING EDITORS

Bob Berman, Adam Block, Glenn F. Chaple, Jr., Martin George, Tony Hallas, Phil Harrington, Ray Jayawardhana, David H. Levy, Alister Ling, Steve Nadis, Stephen James O’Meara, Tom Polakis, Martin Ratcliffe, Mike D. Reynolds, Sheldon Reynolds, John Shibley, Raymond Shubinski EDITORIAL ADVISORY BOARD

Buzz Aldrin, Marcia Bartusiak, Timothy Ferris, Alex Filippenko, Adam Frank, John S. Gallagher lll, Daniel W. E. Green, William K. Hartmann, Paul Hodge, Anne L. Kinney, Edward Kolb, Stephen P. Maran, Brian May, S. Alan Stern, James Trefil

The 10.4-meter Gran Telescopio Canarias, the largest optical telescope in the world, at La Palma, Canary Islands, will host the 2014 Starmus Festival. IAC PABLO BONET

I

magine a gathering where the greatest minds in space exploration, astronomy, cosmology, and planetary science get together for incredible talks, sharing of information, and appreciation of the knowledge we have of space and the universe. And imagine the event takes place at one of the most beautiful places in the world, the Canary Islands, Spain, in the shadow of the world’s largest telescope, and involves making new friends and renewing old acquaintances. Well, that’s the formula for the Starmus Festival. And it really happened in 2011. Plus, thanks to the vision of organizer Garik Israelian, an astronomer at the Institute of Astrophysics of the Canary Islands, it will happen again. Garik and his advisors — Queen guitarist and Ph.D. astronomer Brian May and Russian cosmonaut Alexei Leonov — have announced the 2014 Starmus Festival! Starmus 2014 will take place in the Canaries, at Tenerife and La Palma, September 22–27, 2014. I’m proud to say that Astronomy magazine is the exclusive

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A ST R O N O M Y • JULY 2014

media partner for the conference. The theme will be “Beginnings: The Making of the Modern Cosmos.” I am also writing and editing the book of Starmus 2011 proceedings and talks, titled Starmus: 50 Years of Man in Space, with Israelian and May. It will be published by Robin Rees at Canopus Books in London and will be available this summer and at the 2014 Starmus event. The organizers have already announced a variety of impressive speakers to bring “Beginnings: The Making of the Modern Cosmos” to life. Nobel-Prize-winning astrophysicist Robert W. Wilson; eminent ethnologist, zoologist, evolutionary theorist, and scientist Richard Dawkins; and Nobel Prize winner and chemist Sir Harold W. Kroto will address the big questions: Where do we come from, and where are we headed? Also in attendance will be three Apollo astronauts — Jack Schmitt, Charlie Duke, and Ed Mitchell — as well as five cosmonauts — Leonov, Vladimir Dzhanibekov, Sergei Krikalev, Viktor Savinykh, and Yuri Baturin.

Important astronomers also will speak at this year’s festival, including SETI researcher Jill Tarter and former director of STScI, Robert Williams. And rock legends will put on quite a show: May and Rick Wakeman of the great prog rock band Yes will perform. Starmus 2014 is definitely shaping up to be as much of a thrill as the 2011 festival. Expect to hear more in the weeks leading up to Starmus, and I hope you’ll join Astronomy magazine and me at this exciting event with some of the brightest minds of our time — all under the pristine skies of the Canary Islands. The festival is supported by Gobierno de Canarias, Cabildo de Tenerife, the International Astronomical Union, and the Canary Islands Astrophysics Institute (IAC). For more information, see www.starmus.com. Yours truly,

David J. Eicher Editor

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JULY 2014 ESO/M.R. CIONI/VISTA MAGELLANIC CLOUD SURVEY 47 TUCANAE; NASA/JPLCALTECH NUSTAR

VOL. 42, NO. 7

CONTENTS

24

FEATURES 18 COVER STORY Life inside a globular cluster

38 StarDome and Path of the Planets

52 Enhance your observing with filters

Imagine doing astronomy when 10 thousand 1st-magnitude stars light up your night sky. WILLIAM

RICHARD TALCOTT; ILLUSTRATIONS BY ROEN KELLY

Not seeing enough detail on planets? Light pollution getting you down? In each case, the solution may be a small piece of glass.

HARRIS AND JEREMY WEBB

24 Chandra’s 10 biggest discoveries

44 Ask Astro

MICHAEL E. BAKICH

Target times.

46

For nearly 15 years, this X-ray observatory has shown what happens to material as it approaches a black hole, how dark energy affects galaxy cluster growth, and how many active galaxies populate the cosmos. LIZ KRUESI

30 The universe in X-rays NuSTAR can see X-rays more extreme than any other telescope, opening a new window on the oldest black holes and the newest supernovae. MICHAEL E. BAKICH

46 Gerald Rhemann imaging from near and far

Pluto comes to the fore. MARTIN

With remote observatories in Namibia and the Alpen foothills, this Austrian imager can lock his lens on any comet or nebula he likes. TEXT AND IMAGES BY

RATCLIFFE AND ALISTER LING

GERALD RHEMANN

36 The Sky this Month

Visit Astronomy.com/toc for bonus material — it’s exclusive to Astronomy magazine subscribers. Astronomy (ISSN 0091-6358, USPS 531-350) is published monthly by Kalmbach Publishing Co., 21027 Crossroads Circle, P. O. Box 1612, Waukesha, WI 53187–1612. Periodicals postage paid at Waukesha, WI, and additional offices. POSTMASTER: Send address changes to Astronomy, 21027 Crossroads Circle, P. O. Box 1612, Waukesha, WI 53187–1612. Canada Publication Mail Agreement #40010760.

ON THE COVER A half million stars pack into globular cluster 47 Tucanae. The brilliant night sky would severely challenge any astronomers there.

COLUMNS Strange Universe 9 BOB BERMAN

Secret Sky 14 STEPHEN JAMES O’MEARA

Observing Basics 64 GLENN CHAPLE

56 Hunting aurorae in the Arctic

Cosmic Imaging 66

Astronomy’s editors battled bitter cold and high winds to witness the northern lights. LIZ KRUESI

ERIKA RIX

ADAM BLOCK

Astro Sketching 68

AND KARRI FERRON

QUANTUM GRAVITY

60 12 sweet summer bino treats

Snapshot 7 Breakthrough 8 Astro News 11

Grab your binoculars and explore double stars, asterisms, and star clusters. PHIL HARRINGTON

IN EVERY ISSUE

62 Astronomy tests Celestron’s StarSense This accessory allows you to transform your old go-to mount into one that aligns itself. PHIL HARRINGTON

Letters 9, 64, 66 Web Talk 65 New Products 67 Advertiser Index 71 Reader Gallery 72 Final Frontier 74

ONLINE FAVORITES Go to www.Astronomy.com for info on the biggest news and observing events, stunning photos, informative videos, and more.

The Real Reality Show Discover the true wonders of the universe

Blogs from the Local Group Insight from the editors

Tour the Solar System

Ask Astro Archive

Videos about our planetary neighborhood

Answers to all of your cosmic questions

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EVERYTHING YOU NEED TO KNOW ABOUT THE UNIVERSE THIS MONTH . . .

HOT BYTES >> TRENDING TO THE TOP

SOLAR BLASTS Magnetic field lines on the Sun’s surface twist, tangle, and build up energy. Once they’ve “had enough,” they straighten and release huge flares, say scientists.

CORE REVEALED Astronomers confirm that the Circinus active galaxy’s center has two dust structures: one out to 3 light-years and another at least double that size.

SPACE DUST The Herschel Space Observatory team released its infrared survey of 323 dusty galaxies with varying star-formation rates and chemical compositions.

SNAPSHOT TONY HALLAS NGC 6503; NASA/SDO/THE AIA TEAM SOLAR BLASTS; XRAY: NASA/CXC/COLUMBIA/F. BAUER, ET AL.; VISIBLE LIGHT: NASA/STSCI/UMD/A. WILSON, ET AL. CORE REVEALED; ESA/HERSCHEL/HRSSAG2 AND HEVICS KEY PROGRAMMES/L. CORTESE SWINBURNE UNIV. SPACE DUST

Galaxies discovered

Our knowledge of “island universes” is a recent thing. Galaxies exist in an array of shapes, sizes, and structures. Bound by the gravity that keeps their contents together, they offer astronomers an infinite variety of architecture to study. Only recently, however, has the picture begun to come into sharp focus. In the 19th century, several astronomers noticed that what appeared to be glowing gas clouds visible through their telescopes seemed to show spiral shapes. These unusual “spiral nebulae” intrigued early observers, particularly William Parsons, aka Lord Rosse, whose 72-inch telescope in rural Ireland was then the world’s largest. Rosse, an Irish nobleman and amateur scientist, was never able to resolve the mystery of his fascinating spiral nebulae. Nearly a century later, American astronomer Edwin P. Hubble, working at Mount Wilson Observatory near Los Angeles, suddenly and shockingly solved the mystery. Hubble found a particular type of variable star in the so-called Andromeda Nebula (M31) and was able to show through the star’s brightness that the nebula was exceedingly far away. The Andromeda Nebula was not a cloud within our own galaxy but instead a remote and very large object itself — the Andromeda Galaxy. In a single series of observations, Hubble discovered the nature of galaxies. — David J. Eicher

Spiral galaxy NGC 6503 in Draco is a highly inclined object showing numerous star-forming regions.

W W W.ASTR ONOM Y.CO M

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BREAK

THROUGH Spiral’s gas blows away Bluish tentacles dangle from ESO 137-001, a massive spiral galaxy that lies 220 million light-years away in the constellation Triangulum Australe. The blue threads are streams of gas stripped from the galaxy as it plows through the much hotter gas that permeates the enormous Norma cluster to which it belongs. ESO 137-001 blasts through this intracluster gas, which seethes at 180 million degrees Fahrenheit (100 million degrees Celsius), at nearly 4.5 million mph (7.2 million km/h). The tendrils of stripped gas glow blue from the light of hot massive stars that recently formed in them. NASA/ESA/ THE HUBBLE HERITAGE TEAM STSCI/AURA

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A ST R O N O M Y • JULY 2014


STRANGEUNIVERSE

FROM OUR INBOX

BY B O B B E R M A N

Astronomy for kids

The animated universe

Natural motion dominates the cosmos.

A few months ago, I did something I never thought I would do: I got rid of eight years of my beloved Astronomy magazines! But don’t worry — they found a new home. I donated them to my older daughter’s school library, where they will continue to challenge the minds of young readers for years to come. — César Rodrigues, Slough, United Kingdom

Praise for Bob Berman

N

othing in the universe, small or large, is stationary. Everything moves. In many cases, the motion is as fascinating as the object itself. During early July, the Sun lopes through Gemini 3 percent more sluggishly than it passed through Sagittarius last winter. That’s because Earth now moves at its slowest pace of the year. We’ve been braking for six months. We’ve lost a whopping Mach 3. Meanwhile, the Moon spins so slowly that an elite lunar marathoner could keep the Sun from setting. And our sister planet, Venus, boasts the most lethargic rotation in the known universe, a mere 4 mph (6 km/h). By comparison, most U.S. cities whiz at very nearly the speed of sound. All this squirms through my mind because Little, Brown and Company is just publishing my newest book. The result of two years’ work, Zoom is about natural motion and the wild stories of the forgotten men and women who made brilliant or lucky discoveries — like the man who first figured out why the wind blows. I learned amazing stuff. Some involved astronomical objects, but most were revelations about everyday phenomena. The speed of blood. How fast all that stuff in your intestines creeps along. How slow molasses is. How the magnetic poles shift hourly by the length of a living room. And that relative to their size, bacteria can swim 10 times faster than fish. Some germs can cross a kitchen counter in an hour. I included today’s hottest topics, such as unimaginably fast quantum phenomena and

why distant galaxies seemingly racing at light-speed are actually just hanging out, receding solely because the empty space is expanding between us. My findings were mesmerizing, like the bizarre radiation discoveries a century ago and the lingering mysteries of cosmic rays. Why are these omnipresent incoming particles made almost entirely of heavy protons when there are just as many electrons in the universe? And what about the wild genius who first invented motion pictures before shooting his wife’s lover at point blank range? Zoom’s subtitle is How Everything Moves: From Atoms and Galaxies to Blizzards and Bees. It’s my lengthiest work. And, yes, this is a shameless plug. I can’t help it. It’s got way too much cool stuff to ever find its way onto this page. Did you know that ocean waves arrive every eight seconds? And, using typical values, that

When each issue of Astronomy magazine arrives, I immediately read “Strange Universe.” I am impressed — sometimes stunned — by the almost unbelievable facts and insightful comments about the interconnected universe and the very nature of reality itself. I find this wondrous and exciting! Thank you for your work. — Jerry Richter, Warrensburg, Missouri

Correction The main image on p. 65 of the March issue was not of M86 and M84 but rather NGC 4874 and NGC 4889. We regret the error. — Astronomy Editors

We welcome your comments at Astronomy Letters, P. O. Box 1612, Waukesha, WI 53187; or email to letters@astronomy.com. Please include your name, city, state, and country. Letters may be edited for space and clarity.

And not just far-away things. We may imagine that a compound like water ice, made of two hydrogen atoms bonded electrically to an oxygen atom, has a rigid structure. Not so. The atoms stretch away from each other a bit and then snap back as if on a rubber band. At the same time, they twist around and then return to shape.

UNSEEN VIBRATIONS CREATE DRAMATIC EVERYDAY EFFECTS. they match the speed of cars in moderate traffic? When reaching a shallowing seabed, a wave’s top starts moving faster than its base. The result: It rises and leans forward. When its heightto-wavelength ratio reaches a 1:7 proportion, the wave cannot support itself, and it “breaks.” We often overlook one peculiar kind of motion. Astronomers have found that all celestial bodies spin on an axis while also moving forward, but in addition, everything vibrates. An entire research field called asteroseismology probes the rapid up-and-down pulsations of stellar surfaces.

They also rock back and forth like a metronome. Each of these repetitive atom motions of twisting, stretching, rocking, bending, and wagging recur with a precise period between 1 trillion and 100 trillion times a second. You’d think this shaking would dampen out and stop. It never does. Meanwhile, light itself — the medium that delivers most of what we know about the cosmos — is oscillating waves of magnetism and electricity whose fluctuation rate depends on the color. Green light oscillates 550 trillion times per second. Such motion has in-your-face consequences.

An automobile parked in sunlight heats up, to give one example, because its interior’s infrared waves happen to pulse at a rate matching the natural atomic vibrations of the car’s glass. This creates a chaotic boundary, blocking heat from escaping through the windows the way visible light does. People have been arrested for leaving pets or children in such parked cars. The warrant probably didn’t specify, “Suspect ignored the lethal perils of ultra-fast vibrations,” but that’s what it amounts to. Unseen vibrations create dramatic everyday effects. Don’t you love this kind of stuff? Even our thoughts involve speed, as they traverse the brain at 70 mph (110 km/h). But other nerve signals lope along much more slowly. That’s why, when we stub our toe, there’s that agonizing delay of two or three seconds before we get the bad news. And for now, this is where I too must come to a complete stop. Contact me about my strange universe by visiting http://skymanbob.com.

BROWSE THE “STRANGE UNIVERSE” ARCHIVE AT www.Astronomy.com/Berman. W W W.ASTR ONOM Y.CO M

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ASTRONEWS

CONGRATULATIONS, CONTRAPTION! The European Southern Observatory installed the Multi Unit Spectroscopic Explorer (MUSE) on its Very Large Telescope in Chile. On March 5, the agency announced that MUSE had collected its first light.

QUICK TAKES

RING AROUND A … CENTAUR?

UPCONVERSION

ESO/L. CALÇADA/M. KORNMESSER/N. RISINGER

W

hen scientists planned an exhaustive campaign to observe the asteroid-like object 10199 Chariklo as it passed in front of a distant star from Earth’s vantage point, their goal was to refine the solar system body’s size and determine its shape. Chariklo, the largest member of a class of objects known as centaurs, which have unstable orbits in the region of the giant planets, lies between the orbits of Saturn and Uranus. While the astronomers did learn more about this 155-milewide (250 kilometers) minor planet, their results, which appeared in the April 3 issue of Nature, came as a surprise: Two dense rings encircle Chariklo. “We weren’t looking for a ring and didn’t think small bodies like Chariklo had them at all, so the discovery … came as a complete surprise!” says lead author Felipe Braga-Ribas of the National Observatory in Rio de Janeiro. To date, scientists had only observed rings

CIRCLED CENTAUR. Recent observations of the asteroid-like object 10199 Chariklo have revealed two narrow rings encircling the centaur, as depicted in this illustration.

around four bodies in our solar system — those circling the gas giant planets. But scientists saw four additional dips in the occulted star’s brightness, beyond the expected one, when Chariklo passed in front of the distant sun. The extra dimming brought the rings to light in the same way this method helped astronomers discover the rings of Uranus in 1977. Analysis indicates that the two rings are about 2 and 4 miles (3 and 7km) wide separated by a 5.5-mile (9km) gap.

LIGHT HAS DIRECTION

Although Braga-Ribas’ team doesn’t know conclusively how the rings formed, the results do answer previous questions concerning Chariklo. According to the study leader, observations between the centaur’s discovery in 1997 and today have shown changes in spectral intensity (which indicates composition) and brightness over time. A ring system made of ice that scientists sometimes see head-on but other times view edge-on would explain the data. — Karri Ferron

FAST FACT

Elliptical polarization is similar to circular polarization except the components are shifted by one-eighth wavelength.

Researchers now can detect weak radio signals from space by turning them into visible light. The radio waves cause shifts in a laser beam, which can travel through low-loss optical fibers, according to the March 6 issue of Nature.

MARTIAN MATCH The shergottite meteorites — by far the majority of rocks that flew our way from Mars — came from the Red Planet’s Mojave Crater, according to the March 21 issue of Science.

MIRROR MONEY The University of Texas at Austin committed $50 million March 7 to the $1.05 billion Giant Magellan Telescope, which will take its first observations in 2020.

EURO EXOPLANETS The United Kingdom announced March 11 that it will pledge £25 million to the European Space Agency’s Planetary Transits and Oscillations of Stars mission, which will study exoplanet habitability starting in 2024.

FORESIGHTED The United Kingdom announced March 11 that it will fund £100 million of the Square Kilometre Array (SKA) telescope. In 2011, the U.S. pulled out of the SKA. Ten major nations are involved.

TOO SOON OLD …

Linear polarization

Circular polarization

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LYRICAL LIGHT. Electromagnetic radiation, like visible light, is energy that moves through space as a wave or as a particle. The wave form is made up of an electric wave and a magnetic wave that are always perpendicular to each other. One of the properties of a light wave is its wavelength, which relates to its color; another is its direction, called polarization. When scientists talk about a light wave’s polarization, they refer only to the electric wave’s direction, which is made of up two directional components (X and Y). This illustration shows two types of polarization: linear and circular. These types are a result of the electric field’s components being at different phases from one another. Linear means they’re in phase; circular is when they’re shifted by one-quarter wavelength. ASTRONOMY: LIZ KRUESI AND ROEN KELLY

27,200 (±520) LIGHTYEARS

The most accurate distance yet measured from Earth to the Milky Way’s center, according to a March 10 study in The Astrophysical Journal of more than 100 massive young stars in the galactic core.

Mature galaxies — organized and finished with outbursts of star formation — existed just 1.6 billion years after the Big Bang, reports a paper in the March 1 issue of The Astrophysical Journal Letters. But how? Why? To be continued.

EUROPA REPORT Researchers recreated the surface of Europa inside the Centro de Astrobiología in Spain, they announced March 12, showing that material beneath the icy crust rises to the surface like magma.

CASH FLOW An anonymous donor pledged $4.2 million to The Planetary Society on March 17. Founded by Carl Sagan, the society will use the money to continue existing projects, expand staff, and educate us all. — Sarah Scoles

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ASTROCONFIDENTIAL ASTRONEWS

BY K ARRI FERRON

COURTESY MARK T. REYNOLDS

WHAT ARE WE LEARNING ABOUT BLACK HOLE SPIN?

Mark T. Reynolds Assistant research scientist with the University of Michigan Department of Astronomy, Ann Arbor

ASTRONEWS

Studies of the spin evolution of supermassive black holes versus redshift allow us to study the co-evolution of black holes and their host galaxies across cosmic time. As a black hole accretes gas, depending on the direction of the gas, it may increase or decrease the spin of the black hole, which we measure by studying the X-ray radiation emitted by the multimilliondegree gas orbiting in its direct environment. In this region of space, the strong gravitational potential of the supermassive black hole, as described by Albert Einstein’s general theory of relativity, acts to distort the emitted radiation in a characteristic manner. In our recent study with the Chandra and XMM-Newton X-ray observatories, we measured the spin of the supermassive black hole in the quasar RX J1131–1231 at a redshift corresponding to almost half the age of the universe. To do this, we took advantage of a fortuitous cosmic alignment of a large galaxy along the line of sight that acts as a

Black holes have two main characteristics: mass and spin. While astronomers have been able to measure black hole masses effectively for years, determining their spins has been much more difficult.

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gravitational lens to magnify and distort the emission of the distant quasar. The luminous black hole in RX J1131– 1231 is about 200 million solar masses and consumes vast quantities of matter (about one solar mass per year!). The X-ray emission we detected originates at only two times the radius of the event horizon. Detailed modeling of these X-rays has revealed that this black hole spins at approximately 90 percent of the maximum value allowed by general relativity. This is the most distant black hole for which we have been able to directly measure the spin to date, and its large spin value supports models in which black holes accrete matter preferentially in a coherent manner. There are a number of additional lensed quasars that we hope to be able to study in a similar manner over the coming years. Undoubtedly, exciting times lie ahead in our quest to understand the spin of distant supermassive black holes.

IS IT HOT IN HERE? NASA’s Solar Probe Plus moved into its fabrication and assembly stage March 18. The pioneering spacecraft, to launch in 2018, will fly through the Sun’s corona, traveling in a star-hugging orbit 24 times.

Plasma protects Earth

What to do with all the citizens’ science?

Without Earth’s magnetosphere to protect against the constant stream of solar particles that bombards our world, humans (and our delicate technology) would be toast. It deflects these damaging particles away from our planet. Where that magnetic field meets the Sun’s, though, their “magnetic reconnection” can allow electrical currents to flow straight into Earth’s atmosphere. Geomagnetic storms, which have deleterious effects on high-altitude aircraft and astronauts, can result. Scientists at the Massachusetts Institute of Technology in Cambridge and NASA’s Goddard Space Flight Center in Greenbelt, Maryland, have discovered that the magnetosphere has another trick up its sleeve: a “river of plasma” that acts as a backup weapon in the fight against the life-giving star that easily could kill us. They describe their results in the March 7 issue of Science. The team found cold (in other words, slow-moving) plasma particles from Earth’s lower atmosphere snaking up our planet’s magnetic field lines, traveling to the points where magnetic reconnection occurs. The plasma plumes slow reconnection events, shielding Earth from

In your free time, you can classify galaxies, count craters, and dissect stardust. Dozens of astronomy-based citizen science projects exist online, giving anyone with a computer and an Internet connection the opportunity to join the research world. But the role of citizen science is unclear to the professional scientific community. In a “Policy Forum” article published in the March 28 issue of Science, Rick Bonney of Cornell University in Ithaca, New York, and collaborators lay out both the problems and some solutions. Science that requires “big data” — terabytes of data, billions of samples, geographic spread — also requires big analysis. Sometimes, computers can shoulder that task, but sometimes human beings still do the job best (for example, if it involves pattern recognition). For a scientist, harnessing the power of the population makes the work go a lot faster than harnessing the power of her five collaborators. But how can the scientists ensure that the work of amateurs is robust and reliable enough to “count”? That uncertainty has been the primary barrier to wide-ranging acceptance of citizen-obtained conclusions. Bonney and his co-authors suggest that scientists hold their citizen science methods to the same standards they would their own research. Then, they say, let the peer-review process decide whether the results are worthy. If they are, no stigma should be attached simply because all participants don’t have Ph.D.s. In addition, if project developers work together to combine similar projects and processing methods, the standardization will increase efficiency and reliability. In the astronomical world, the Zooniverse citizen science platform attempts to accomplish this. The organization created software, algorithms, and tutorial templates that can jump-start vetted projects. Perhaps astronomy is ahead of the curve. — S. S.

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A ST R O N O M Y • JULY 2014

SHIELDS UP! The Sun is always sending charged particles — and sometimes larger ejections, as illustrated here — in our direction. Earth’s magnetosphere deflects these particles, and scientists recently discovered that plasma plumes from its lower atmosphere do too. CHRISTINE DANILOFF/MIT

some of their effects. To find these plumes, astronomers watched for distortions in GPS satellite signals. From the distortions’ details, they made 2-D maps of the atmospheric plasma. They then used satellites to look down at the same plumes detected from the ground. The plasma, they found, went all the way up, tens of thousands of miles. “A new set of ground-based observations can be used to infer what is occurring deep in space,” says Tony Mannucci of the Ionospheric and Atmospheric Remote Sensing Group at NASA’s Jet Propulsion Laboratory in Pasadena, California, “allowing us to understand and possibly forecast the implications of solar storms.” — S. S.


ASTRONEWS Earth

NEW LEADERSHIP. The Smithsonian Astrophysical Observatory stated March 19 that Belinda Wilkes will head the Chandra X-ray Center.

Kepler-186 system

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Habitable zone

Solar system Sun Earth

Venus

Mercury

EARTH’S COUSIN? As a red dwarf star, Kepler-186 is cooler and gives off less energy than the Sun; thus its habitable zone (HZ) is closer in. This diagram compares our solar system to the Kepler-186 system. Kepler-186f is an Earthsized planet orbiting within the HZ, making it the most similar world to Earth yet found. NASA AMES/SETI INSTITUTE/JPLCALTECH

Earth-sized world in “Goldilocks” zone Nearly 500 light-years away lies a star with a world just 10 percent larger than Earth orbiting within its habitable zone (HZ) — the region around the sun where water could exist in liquid form on the exoplanet’s surface. Astronomers have found about 20 other exoplanets in their stars’ HZs, but this new one, called Kepler-186f, is the most similar in size to Earth. The new study, which appeared in the April 17 issue of Science, “shows that Earth-size planets can and do exist in the HZs of other stars,” said NASA’s Exoplanet Exploration Program Scientist Doug Hudgins during a press conference announcing the discovery. Kepler-186f orbits a red dwarf star that is 47 percent of the Sun’s width and about 66 percent of our star’s temperature. Using the Kepler space telescope’s first two years of data, scientists found the signatures of four planets orbiting the star with periods between 3.9 and 22.4 days.

These worlds lie between 0.04 and 0.13 astronomical unit from their star (where 1 AU is the average Earth-Sun distance). An additional year of observations allowed Elisa Quintana of the SETI Institute and colleagues to tease out Kepler-186f orbiting 0.36 AU from the red dwarf. The star’s HZ extends from 0.22 to 0.40 AU, placing this newfound world near the outer edge. There, the exoplanet receives about 32 percent of the intensity of radiation from its star as Earth receives from the Sun. Quintana’s team measured Kepler-186f’s width: 1.11 times Earth’s. Their observations, however, tell them nothing about the exoplanet’s mass, which means they cannot calculate the composition. They also can’t observe the planet with enough detail to spy evidence of an atmosphere. Whether this planet has surface water, an atmosphere, or any type of life are still open-ended questions. — Liz Kruesi

AVERAGE NUMBER OF CLEAR DAYS IN JULY

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ASTRONOMY: MICHAEL E. BAKICH AND ROEN KELLY, AFTER NOAA

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SECRETSKY

Cold as space

The bewitching Fata Morgana This strange atmospheric phenomenon causes multiple images of a single object to materialize out of thin air.

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he Strait of Messina between Sicily and Southern Italy has long been associated with one of the most fascinating mirages known: the Fata Morgana. Italian for “Morgan the fairy,” the phenomenon is named after the fabled fairy/ witch Morgan le Fay — featured in Arthurian legends — who used her mystical powers to conjure up images of castles in the air. These fanciful visions bewitched sailors, leading them into danger. Some believed that one special optical illusion — a looming palace — was le Fay’s enchanted island dwelling. Truth is, le Fay’s magic isn’t required to see this beautiful natural event, nor do we have to be on or near the sea … or in Italy. The phenomenon can occur at any longitude or latitude. All we need is for a string of complex variables to come together to create the right atmospheric conditions for this “castle” to appear. Seeing it also requires awareness and perseverance.

Bewildering phenomenon

Supernova hot

Sciencegate

Travel advisory

Sexy space

Cramped quarters

Enrico Saggese resigns from the Italian Space Agency after potential fraud and unofficial agency-sponsored vacations. It’s about time astronomers started acting more like politicians.

The General Authority of Islamic Affairs & Endowment deems travel to Mars tantamount to suicide and disallows it for Muslims. Easier excuses do exist for getting out of a trip to the Red Planet.

In the most sensual sentence ever about pulsars, NASA titles a press release “With A Deadly Embrace, ‘Spidery’ Pulsars Consume Their Mates,” titillating and spurring new interest in science.

The Olympic torch rides on the ISS before arriving in Sochi, seen here from orbit, February 7. After seeing its Russian hotel room, it asks to go back to that metal box with artificial air.

buildings ever shrinking then climbing in the shimmering air. Even a distant frozen sea can rear up into a Fata Morgana, and early polar explorers eager to sight undiscovered lands were known to mistake this apparition for mountainous land.” On December 2013, I had the fortune of spying le Fay’s handiwork from a hillside outside Fairbanks, Alaska. At first, I saw a series of inverted castles in the air above a distant peak. Two minutes later, the airborne castles had melted into a single fortress with two spires. Two minutes after that, the castle had deformed into a massive flattopped plateau.

Historical wonder In written records, whispers of the Fata Morgana can be traced to at least 1531, when German magician and occult writer Heinrich Cornelius Agrippa recorded the phenomenon in his Of Occult

Philosophy, Book III. An even earlier observation came from Italian scholar Antonio de Ferrariis in 1508, but it was not published until 1558. In his book about the region of Italy now known as Apulia, de Ferrariis wrote that the formations do not last long but change “as the vapors in which they appear, from one place to another, from one form to another.” Sometimes, he wrote, “you will see cities and castles and towers, and sheep and different colored cattle and images or specters of other things.” By the way, the plot of Sergei Prokofiev’s 1921 opera, The Love for Three Oranges (based on an Italian fairy tale), included a curse from the witch Fata Morgana and the casting of a magic circle by the sorcerer Agrippa. Get out there and try to detect this illusion. As always, let me know what you see and don’t see at sjomeara31@gmail.com.

STEPHEN JAMES O’MEARA

An elaborate type of “superior mirage” (meaning the mock

object materializes above the position of the real object), the Fata Morgana forms during strong temperature inversions. When a layer of warm air blankets a layer of cold air, the combination causes a rise in the temperature with altitude, the opposite of a normal situation. In the Fata Morgana, light rays from distant objects travel across the interface between the cold and warm air layers in disparate curved paths to reach our eyes. Consequently, the light from these objects smears out vertically. The rays also can be magnified, multiplied (with alternating erect and inverted components), and distorted. Classically, the Fata Morgana has three or more false images, which can change shapes in a matter of seconds. The shapes an observer sees also vary with position relative to the cold/ warm air boundary. “Not all inversions give a Fata Morgana,” explains Les Cowley, who runs the website Atmospheric Optics, “but when they do, we are confronted with a wondrous prospect of otherwise ordinary distant hills transformed into impossibly tall multilayered cliffs, towers, and

A look at the best and the worst that astronomy and space science have to offer. by Sarah Scoles

ESA SCIENCEGATE; NASA/JPLCALTECH/MSSS TRAVEL ADVISORY; GODDARD SPACE FLIGHT CENTER SEXY SPACE; NASA CRAMPED QUARTERS

COSMIC WORLD

BY STEPHEN JAMES O’MEAR A

In Fairbanks, Alaska, Stephen James O’Meara witnessed the optical phenomenon known as the Fata Morgana, in which temperature inversions cause rapidly changing optical illusions. BROWSE THE “SECRET SKY” ARCHIVE AT www.Astronomy.com/OMeara.

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A ST R O N O M Y • JULY 2014


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ASTRONEWS

pH UNPLEASANTNESS. When the Chicxulub asteroid smashed into Earth 65 million years ago, the impact may have created

sulfuric acid aerosols that turned the surface oceans into acid baths within a few days, say scientists in the April Nature Geoscience.

NEW “DWARF PLANET” FOUND

Ten years after scientists discovered Sedna, the most distant object seen to orbit the Sun, they’ve found another body in the same region. Called 2012 VP113, this new object travels around our star in an highly elliptical orbit, bringing it as close as 80 astronomical units (AU, where 1 AU is the average EarthSun distance) to the Sun and as far away as about 450 AU. By finding a second object with an orbit similar to Sedna’s, scientists have confirmed that the area they’re calling the inner Oort Cloud exists — a region that lies outside the Kuiper Belt, where Pluto and its friends orbit, but inside the part of the Oort Cloud that harbors comets. Chadwick Trujillo of the Gemini North Observatory in Hawaii and Scott Sheppard of the Carnegie Institution for Science in Washington, D.C., went looking for distant solar system bodies in November and December 2012 with the new Dark Energy Camera attached to the 4-meter Victor M. Blanco Telescope in Chile. They imaged sixteen 2.7-square-degree fields three times each and used a software program to sift through the photos to find changing signals. And sure enough, the program spotted 2012 VP113 in the November 5 observations. After studying the object further with the 6.5-meter Magellan Walter Baade Telescope in Chile’s Atacama Desert in March, August, and October 2013, Trujillo and Sheppard determined its orbit and thus its nearest and farthest approaches to the Sun. They also analyzed 2012 VP113’s color and

SOLAR ACTIVITY SCALES

2012 VP113 Sedna Jupiter’s orbit Kuiper Belt

Sun Saturn’s orbit

Neptune’s orbit

Uranus’ orbit

SCOTT S. SHEPPARD/CARNEGIE INSTITUTION FOR SCIENCE

SPACE SCIENCE UPDATE

NEW WORLD. Scientists found a rocky body with an orbit (red) that brings it as close to the Sun as 80 astronomical units (1 AU is the average Earth-Sun distance) and as far out as about 450 AU. This object, called 2012 VP113, is the second known member of the inner Oort Cloud; Sedna, discovered in 2003, is the first.

how much sunlight it reflects; these two things tell them about the object’s surface, which they can use to calculate its size. The object is about 280 miles (450 kilometers) wide — about the distance between Philadelphia and Providence, Rhode Island. Sedna is roughly twice as big, at 620 miles (1,000km) wide, and has an orbit that takes it some 1,000 AU from the Sun. The scientists describe their discovery in the March 27 issue of Nature. In their paper, Trujillo and Sheppard also note that the two inner Oort Cloud members share similar orbit angles with a few distant Kuiper Belt objects. They ran computer simulations to try to match these orbits. The model that best matches observations indicates that a planet a few times Earth’s mass could shepherd the smaller Sedna-like bodies as it orbits the Sun from about 200 AU out. That planet — if it exists — could have formed much closer to the Sun but then was launched much farther out during a period of upheaval in the early solar system. — L. K.

Light from solar flares takes eight minutes to arrive at Earth, while ejections take days.

FAST FACT

Earth to scale

BIG/SPICY. The Sun is huge. But seeing Earth in comparison slams the point home. A solar prominence from August 31, 2012, dwarfs our planet (left). Active Region 44, which released a large flare February 22 (above), shows even sunspots are bigger than our world. ASTRONOMY: Earth to scale

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A ST R O N O M Y • JULY 2014

SARAH SCOLES AND ROEN KELLY, AFTER NASA/SDO/GSFC PROMINENCE; NASA/SDO SUNSPOTS

CAUSE: COMET CRASHES? Astronomers found a massive clump of carbon monoxide orbiting between about 50 and 100 times the Earth-Sun distance from Beta Pictoris. They suggest a large planet could be shepherding comets into two densely packed regions where their collisions produce the gas. NASA’S GODDARD SPACE FLIGHT CENTER/F. REDDY

Young planetary system may host colliding comets Astronomers have known for several years that the young star Beta Pictoris, which lies roughly 63 light-years from the solar system, has a dusty surrounding disk with an embedded 7-Jupitermass planet. But they’ve now found carbon monoxide distributed along the disk with about one-third of the gas in one clump using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. “The most abundant source of carbon monoxide in a young solar system is collisions between icy bodies, from comets up to larger planet-sized objects,” says the ALMA Observatory’s William Dent. But ultraviolet radiation breaks up carbon monoxide gas in about 120 years, so unless a planet collision occurred around Beta Pictoris within the past century, something, like frequent comet crashes, must be replenishing the reservoir. Dent and colleagues used ALMA to spy on the planetary system and find the carbon monoxide cloud, which lies between about 50 and 100 times the Earth-Sun distance from Beta Pictoris. This clump is nearly one-quarter of the Moon’s mass (or about 16 trillion times as much as the largest freight trains on Earth). The scientists describe their discovery in the March 28 issue of Science. Because the Beta Pictoris dust disk is aligned edge-on to Earth, the astronomers propose that the disk actually holds two patches of carbon monoxide along our line of sight. If this is the case, an as-yet-unseen 10-Earth-mass planet could shepherd comets into two regions. There would be so many comets in those two densely packed areas that collisions would occur frequently (about once every five years) and replenish the gas. This is the most likely scenario, say the scientists. If, instead, the disk hosts one large clump of carbon monoxide, Dent’s team suggests two Mars-mass planets collided recently to produce the observed amount of material. Future observations of the Beta Pictoris system are needed to figure out which scenario proves true. — L. K.


Telescopes.net

TWINKLE, TWINKLE, GIANT STAR After analyzing observations spanning more than 60 years, astronomers say the yellow hypergiant star V766 Centauri is some 1,315 times wider than the Sun, making it the largest yellow star known. The star also has a companion sun, which is so close to V766 Cen that they’re always touching. The new findings appeared in the March issue of Astronomy & Astrophysics.

POLLUTED STELLAR REMNANTS

A study published online March 25 in Monthly Notices of the Royal Astronomical Society describes the abundances of elements in the atmospheres of 89 white dwarfs — the remnants of Sun-like stars. The white dwarfs display heavier elements than expected. The researchers suggest that the remnants accumulated material from rocky bodies — like terrestrial planets and asteroids — that orbited the original stars. — L. K.

NASA/JPLCALTECH/UNIV. OF ARIZONA

FAST FACT

Additional Mars Reconnaissance Orbiter image pairs of similar channel changes at other sites indicate that this type of activity generally occurs in martian winter.

New Mars gully channel appears FEATURE FIND. A comparison of images taken by NASA’s Mars Reconnaissance Orbiter in November 2010 and May 2013 has revealed a new gully channel on the Red Planet. The orbiter uncovered this feature on the slope of a crater wall in the martian southern highlands. According to Mars researchers, the channel probably formed when melted material, likely carbon-dioxide frost, flowing down from the top of an alcove broke out of an older route and eroded a new path. NASA released the image March 19. — K. F.

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NEW STRUCTURE SEEN Astronomers mapping the universe’s large-scale structure across the southern sky have detected strings of galaxies where they didn’t expect them. These newly seen “tendrils” exist within enormous voids of presumed empty space. The Galaxy and Mass Assembly survey team published their findings in the May 1 issue of Monthly Notices of the Royal Astronomical Society Letters.

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Night of a thousand suns

Life inside a GLOBULAR CLUSTER Imagine doing astronomy when 10 thousand 1st-magnitude stars light up your night sky. That would be the task facing scientists living in 47 Tucanae. by William Harris and Jeremy Webb

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hat would the night sky look like from inside a globular cluster? This question has inspired scientists, artists, and space enthusiasts for at least two centuries, ever since astronomers realized that these objects pack hundreds of thousands of stars into fairly small spheres. Perhaps no one explored the possibilities better than Isaac Asimov, who in 1941 wrote the short story “Nightfall” about just such a situation. Asimov set his tale on the fictional planet Lagash, which, unbeknownst to the native population, lies in the middle of a dense star cluster. The plot throws in an extra twist by having Lagash orbit within a system that holds six stars. At least one of these suns is always “up,” so perpetual daylight bathes the planet. Nobody alive has ever experienced night, let alone knows anything about what might exist beyond their own little planetary system. William Harris and Jeremy Webb are both in the Department of Physics and Astronomy at McMaster University in Hamilton, Ontario. Harris is a professor who has studied globular clusters over his career; Webb is completing his Ph.D. thesis on the orbital dynamics of star clusters in large galaxies.

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33 LIGHT-YEARS FROM THE CORE The Milky Way’s disk and the core of globular cluster 47 Tucanae vie for attention in the sky above a hypothetical planet located 33 light-years (10 parsecs) from the cluster’s center. COMPUTER SIMULATION: WILLIAM HARRIS AND JEREMY WEBB MCMASTER UNIVERSITY; BACKGROUND GALAXY: NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA

Although just 2° of sky separate 47 Tucanae (lower right) from the Small Magellanic Cloud (left), a Milky Way satellite located some 200,000 light-years from Earth, the two are not gravitationally connected. G. BRAMMER/ESO

spend their lives orbiting the galactic center, and most of them have done so for more than 12 billion years. They were among the first stellar systems to condense from the original supply of gas that emerged following the Big Bang. While about half of the Milky Way’s globular clusters orbit closer to the galaxy’s center than our Sun does, the more distant ones have orbits that carry them well into the galaxy’s vast spherical halo, even beyond 330,000 light-years (100,000 parsecs; 1 pc equals 3.26 lightyears), where they can take a billion years to orbit the galaxy’s core. Every galaxy except for the tiniest dwarfs has its own retinue of globular clusters. The largest galaxies can hold an astonishing number of these behemoths. The supergiant elliptical galaxy M87 that lies at the center of the Virgo cluster, for example, has 13,000 of them. And even larger systems exist.

Not too hot, not too cold But once every 2,000 years or so, the orbits of five of the stars bring them around to the same direction in the sky, and the sixth one is eclipsed by a normally invisible moon. Lagash then finally experiences true night — and the rest of the universe suddenly becomes visible. None of the residents is prepared for the darkness; after all, who would bother to invent artificial lighting, for example, if it’s always daytime? Asimov presents an arresting image of what deep night on Lagash would be like for its terrified inhabitants: “Not Earth’s feeble thirty-six hundred Stars visible to the eye. … Thirty thousand mighty suns shone down in a soul-searing splendor that was more frighteningly cold in its awful indifference than the bitter wind that shivered across the cold, horribly bleak world.” But would the night sky inside a globular cluster really look like Asimov’s vision of myriad stars spread across a pitch-dark sky?

Giants from the early universe To answer this question, we created a hypothetical Earth-like planet that we could place anywhere inside a simulated but realistic globular cluster. About 160 such clusters scatter throughout our Milky Way Galaxy. These giant, deceptively simple-looking systems of stars

To design our hypothetical Earth-like world, we wanted to make our creation as realistic as possible. Our first step was to abandon the intriguing but improbable idea that the planet could reside in a multiple-star system. Binary and larger systems are fairly rare within dense globular clusters. Worse, however, is the problem of finding a stable orbit for the planet. The task is already difficult in a two-star system, let alone one with three or more stars. The two most common possibilities would have the planet orbiting either well outside the star system, in which case it likely would be too cold for life, or so close to one star (to prevent being pulled away by the companions) that it would be a roasting, Mercury-like world. To avoid these problems, we decided to place our Earth clone in orbit around a single star and at a distance where it would be in the “habitable zone” where surface liquid water and life can exist. Second, we wanted the star itself to be a quiet, well-behaved one on the main sequence, the stage in its life when it generates energy by fusing hydrogen into helium in its core. And, like the Sun, it should have a comfortably long lifetime to allow intelligent life to evolve. Fortunately, these criteria aren’t too restrictive because most stars in globular clusters are still on the main sequence. Our third condition required the cluster to have a relatively high “metallicity,” a term astronomers use to describe the amount of elements heavier than helium. Exoplanet studies show that the W W W.ASTR ONOM Y.CO M

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AT THE CLUSTER’S CENTER From the core of 47 Tucanae, the sky is awash with bright stars. “Night” features some 10 thousand 1st-magnitude or brighter luminaries and more than 130,000 nakedeye suns. COMPUTER SIMULATION: WILLIAM HARRIS AND JEREMY WEBB MCMASTER UNIVERSITY; BACKGROUND GALAXY: NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA

Hundreds of thousands of stars pack into 47 Tucanae, making it one of the larger globular clusters in our galaxy. This groundbased view shows the entire cluster and starts to resolve some of its stars. ESO/DSS2

probability of finding planets around a star goes up with its metallicity, and, in any case, a system needs these heavy elements to build rocky planets. Choosing a highmetallicity globular means that the cluster will spend most of its time orbiting pretty close to the galactic center because that’s where astronomers find most such stellar conglomerations. Almost all of them lie closer to the core than the 27,200 light-years (8,340 pc) distance where our Sun resides. Thus, if we could see the broad swath of the Milky Way’s disk across our model planet’s night sky, it would look at least as big and bright as it does from Earth. Finally, statistics will argue that more planets will be found in larger clusters with more stars. Putting all the conditions together meant we wanted to put our hypothetical planet around a single Sun-like star within a fairly big, high-metallicity globular cluster.

Into the jaws of 47 Tucanae With these guidelines in mind, we developed a detailed computer simulation of a globular cluster. This model allowed us to place our planet at any point inside the cluster and then generate a realistic picture of the sky from that vantage point. Because the simulated cluster includes complete information about all of the model’s stars, we can calculate how far away every individual star is from our imagined location, how bright it appears (its apparent magnitude), what its color would look like to the human eye, and how much total light our Earth-like planet would receive from the entire cluster. The model cluster we built for this purpose contains 570,000 stars and has an average metallicity and structure similar to those of 47 Tucanae (NGC 104). This globular cluster, which lies deep in the southern sky in the constellation Tucana, is the prototype of a highmetallicity cluster in the Milky Way. Although 47 Tuc is not our galaxy’s biggest globular cluster, it is fairly representative and fits most people’s mental image of what such a cluster looks like. We started with a mix of stars of different masses and then used standard stellar evolution models to evolve all of them up to a normal cluster age of 12 billion years. (We chose the initial mix of stars to yield the right relative numbers of main sequence stars, red giants, white dwarfs, and neutron stars observed after 12 billion years.) A cluster like this will take roughly 100 million years to complete one orbit around the galaxy’s center — comfortably long enough for 20

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life to evolve significantly and for the galaxy to stay in pretty much the same place in the sky from the viewpoint of stargazers on our imagined planet. In contrast, the stars inside the cluster will have typical elliptical orbits with periods of a million years around its own center. If we imagine a long-lived civilization with good record keeping, the people there would be able to report on the night sky’s steadily changing appearance as their planet moves in toward the cluster’s center and back out again. Just for fun, we decided to run our visualizations with the cluster at its farthest distance from the galactic center (about 33,000 lightyears, or 10,000 pc). And we chose an orbit that has carried the cluster up and well away from the galaxy’s disk into the halo. As a stand-in for our galaxy in these images, we picked a recent Hubble Space Telescope mosaic of the nearby spiral galaxy M83, which is only slightly bigger than the Milky Way.

Diving into the cluster’s core Our first snapshot of the planet’s sky (above) comes from a point in the cluster’s core. All stars are color-coded by their surface temperatures. The luminous but rare red giants, stars that recently evolved


off the main sequence, appear a deep orange; slightly less evolved subgiants and main sequence stars show a yellow or white hue. At the center, our planet would be surrounded by a few hundred stars per cubic light-year (several thousand stars per cubic pc), which is thousands of times the stellar density of the Sun’s neighborhood in the Milky Way’s suburbs. The typical distance from our hypothetical planet to the closest star, however, still would be substantial — about 0.05 light-year (0.015 pc). In our solar system, this would place it beyond the inner edge of the Oort Cloud of comets. Unless the closest stars happen to be red giants, none of them would have angular diameters large enough to resolve with the human eye, so all the stars still would appear as points of light. Across the entire sky, inhabitants of our hypothetical world would see 10,000 stars brighter than 1st magnitude — compared with just 29 in Earth’s sky — and more than a thousand brighter than Earth’s most brilliant nighttime star, Sirius. The brightest suns would blaze at apparent magnitudes brighter than –9, or 100 times more luminous than Venus appears from Earth. More than 130,000 stars would shine brighter than 6th magnitude, the naked-eye limit, compared with 6,000 from Earth.

Although it might sound like lots of empty space still exists at the cluster’s center, the prospects for doing astronomy from there would be discouraging. The biggest problem would be the sheer amount of light from all those stars. The cluster’s suns would combine to give an average sky brightness some 20 times brighter than Earth’s night sky at Full Moon (or about 16.7 magnitudes per square arcsecond). In other words, the darkest night our viewers would ever see would be a strange sort of twilight that possesses a kind of grainy texture unlike the uniform sheet of light we see on Earth. The galaxy’s disk — already hard to see from Earth at Full Moon except from isolated locations — would be visible in the background but hard to study. Astronomers on our hypothetical planet likely would favor telescopes with small fields of view and excellent baffling against scattered light. It might seem that stellar astrophysicists, at least, would have a field day from their perch because they could observe nearby stars at most evolutionary stages. But knowing the physical properties of stars first requires measuring their distances, and that wouldn’t be easy. The gold-standard method is trigonometric parallax, in which observers measure the apparent shift of a star relative to a distant background of “fixed” stars as the planet orbits its sun. In the cluster W W W.ASTR ONOM Y.CO M

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8.2 LIGHT-YEARS FROM THE CORE From a vantage point 8.2 light-years (2.5 parsecs) from 47 Tucanae’s center, half of the cluster’s stars lie interior to our hypothetical planet’s position. The cluster’s central regions still dominate the sky while the Milky Way looms almost equally impressive. COMPUTER SIMULATION: WILLIAM HARRIS AND JEREMY WEBB MCMASTER UNIVERSITY; BACKGROUND GALAXY: NASA/ESA/THE HUBBLE HERITAGE TEAM STSCI/AURA

Astronomers captured this image of 47 Tucanae through the Visible and Infrared Survey Telescope for Astronomy at Paranal Observatory in Chile. Because it includes some infrared wavelengths, the view highlights cooler, redder stars. ESO/M.R. CIONI/VISTA MAGELLANIC CLOUD SURVEY

This Hubble Space Telescope view of 47 Tucanae reveals some 35,000 stars in the densely packed center of the cluster. The colors match what the human eye would see, with the reddish stars being mostly giants near the end of their lives and the yellowish ones more Sun-like objects. NASA/RON GILLILAND STSCI

environment, few background stars would be visible because the cluster lies out in the galaxy’s halo where field stars are few and far between. It would be difficult just to start measuring parallaxes. Once scientists invent radio and X-ray telescopes, though, a lot of the outside universe would become detectable, but interpreting all those strange new signals would pose a challenge without the optically visible cosmos to compare them with. It would be vital for astronomers to make observations from orbit, where dark sight lines 22

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between the stars would exist and instruments could peer through them free of the blurring and diffusing effects of the atmosphere. And here, deep in the cluster’s core, other factors would make life dangerous. There would be a non-negligible possibility that a close encounter with a nearby star could disrupt the planet’s orbit or even strip the world from its host star. The core of a large globular cluster also typically harbors dozens of millisecond pulsars or low-mass X-ray binaries — violent objects that would bathe the world in highenergy radiation if it ventured too close. And if the cluster happens to be one of the “lucky” ones that contains a central black hole, the planet’s next trip through the core could be its last. All in all, the center of a big cluster doesn’t seem like a good neighborhood to live in.

Welcome to the suburbs Luckily, the planet and its parent star spend most of their time well outside the cluster’s core. If we follow our planet as its star orbits farther out, we discover a wonderfully different picture. To illustrate this, we modeled what the night sky would look like with the planet 33 light-years (10 pc; see p. 18–19) and 8.2 light-years (2.5 pc; above) from the cluster’s center. (The 8.2-light-year [2.5 pc] location lies at


the “half-mass radius” that encloses precisely half of the cluster’s mass and approximately half of its stars.) From either of these viewpoints, the world is still well inside the cluster. Stars remain gravitationally bound to the cluster out to a radius of about 165 light-years (50 pc). But once we move outside the cluster’s core, far fewer nearby stars would hinder the view because the number of suns per unit volume drops roughly as the cube of the distance. By far the brightest thing in the night sky would be the main body of the cluster, but the disk and central bulge of the Milky Way Galaxy would loom behind it all and stretch halfway across the sky. What kinds of fascinating mythologies would be built around this awesome view in early pre-literate cultures? Although parallax measurements still would pose problems, doing astronomy from either of these vantage points would in some ways be better than from Earth. Observers would have a fine view of the entire galaxy and would not have to struggle, as earthbound astronomers have for decades, to disentangle the dimming and reddening effects of interstellar dust that mar the view from within the

galactic disk. And by looking directly away from the center of the cluster, skygazers would have an uninterrupted panorama of the deep sky. This view would provide a perfect lead-in to studying galaxies and cosmology. But an important shortcoming from these locations would be the difficulty in investigating the early stages of stellar evolution, starting with the interstellar clouds of gas and dust that give birth to stars and the subsequent life cycles of the most massive, short-lived stars. All these objects live in the galaxy’s disk and spiral arms. Although they would be visible from farther out in the cluster, astronomers would have to study them from longer range. All in all, though, the night sky from these vantage points would be an exciting and wonderful thing to see. If we were free to choose, there’s no doubt we would vote for one of these outer two spots. In the end, the answer to our original question about what the night sky would look like from inside a globular cluster depends crucially on exactly where we imagine putting ourselves. In some ways, Asimov came pretty close to hitting the mark.

TO WATCH A VIDEO THAT TAKES YOU FROM EARTH’S SURFACE INTO THE HEART OF 47 TUCANAE, VISIT www.Astronomy.com/toc. W W W.ASTR ONOM Y.CO M

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High-energy cosmos The supernova remnant Cassiopeia A was one of the first objects astronomers targeted with the Chandra X-ray Observatory. When the data came in, astronomers were ecstatic to see the point source at the remnant’s center: a neutron star (visible as a turquoise dot), the dense core of a massive sun that exploded as a supernova centuries ago. NASA/JPLCALTECH/STSCI/CXC/SAO CASSIOPEIA A; NGST CHANDRA XRAY OBSERVATORY

Chandra’s biggest discoveries

For nearly 15 years, this X-ray observatory has shown what happens to material as it approaches a black hole, how dark energy affects galaxy cluster growth, and how many active galaxies populate the cosmos. by Liz Kruesi


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Galaxy cluster growth reveals dark energy

Astronomers have used Chandra to study many of the universe’s puzzles, including dark energy, the mysterious “force” that’s Astronomers studied 86 clusters of galaxies speeding up cosmic expansion. Specifiat different cosmic epochs, including Abell 85 cally, scientists measured if dark energy shown here, to figure out how their masses affects the formation and growth of clus- and numbers change as a function of time. XRAY: NASA/CXC/SAO/A. VIKHLININ, ET AL.; OPTICAL: SDSS ters of galaxies. In a study published in 2009, Alexey Vikhlinin of the HarvardSmithsonian Center for Astrophysics in Cambridge, Massachusetts, and colleagues measured the masses of 86 galaxy clusters from two different cosmic epochs (49 from the present-day cosmos and 37 from about 5.5 billion years ago) to see if their growth depends on when in the universe’s lifetime they formed and grew. They calculated the masses of those galaxy clusters from the temperatures and densities of their X-ray-emitting gas, and they found that structure growth has slowed in the past 5 billion years. The astronomers then compared the measured masses of the observed clusters to simulations of cosmic structure, noting when a model matched what they observed. “We can explain all aspects of evolution of the clusters’ weight only with models with dark energy,” said Vikhlinin in a press conference announcing the findings. Scientists can combine these dark energy constraints with what they’ve learned about this “force” from different measurement techniques — like those based on exploding stars called type Ia supernovae and on the glow of the cosmic background radiation from just 380,000 years after the Big Bang. When they incorporate all these studies, they can narrow down how much of the universe is composed of dark energy and gain hints of what it might be.

NASA/CXC/IOA/A. FABIAN, ET AL.

ON

August 26, 1999, scientists with the Chandra X-ray Observatory held a media briefing to reveal the new space telescope’s first images. As usually happens during one of these events, the team chose a pretty object to capture, something the public would like to see; they decided on Cassiopeia A, the remnant of a massive star’s supernova explosion. “We were supposed to look amazed looking at the screen as the data from Cas A came in,” says Chandra Project Scientist Martin Weisskopf of NASA’s Marshall Space Flight Center in Huntsville, Alabama, “but it turned out we were amazed because all of a sudden at the center of Cas A was a bright point-like object that had not been seen before.” That bright point is a neutron star, the leftover core of the once-massive sun. Astronomers had theorized that Cas A contained such an object, but before Chandra no one had seen it. During the nearly 15 years since that day, the Chandra team has uncovered many similarly astounding discoveries. This observatory certainly wasn’t the first X-ray satellite, but it has a remarkable ability: unparalleled angular resolution. It can distinguish details as small as 0.3 arcsecond across; that’s equivalent to the size of a quarter 10.4 miles (16.7 kilometers) away. Chandra’s amazing vision shows astronomers X-ray emission from the hottest objects in the universe, like exploding stars, the regions surrounding active black holes, giant clusters of galaxies, and newborn suns. “It allows us to see things that we couldn’t see before,” says Weisskopf. And from that incredible resolution, scientists have unraveled many of the universe’s high-energy secrets, including how supermassive black holes affect galaxy growth, properties of the universe’s mysterious dark matter, and the details within supernova remnants. These three and seven more of Chandra’s 10 most important discoveries highlight the space telescope’s career, and the mission isn’t over yet.

With Chandra, astronomers have found about a hundred supermassive black holes clearing gas and creating cavities in their host galaxies. These bubbles, which extend hundreds of thousands of light-years, also initiate shock fronts. Such wave-like patterns are visible in X-ray images of galaxy Perseus A, which is shown here.

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Black holes “blow” bubbles

Every large galaxy harbors a supermassive black hole at its center. And every cluster of galaxies holds hundreds or thousands of individual galaxies, with the largest near its core. By studying the X-ray emission from the hot gas within these clusters, astronomers are learning about the violent events that happen in such environments and the features that result. Often, the central galaxy is active as its black hole dines on nearby material and blows off radiation. Scientists have found that the black hole at the center of the most massive cluster member affects not just its host galaxy but also the cluster it lies in. In an active galaxy, the black hole’s immediate surroundings emit high-energy jets of radiation and particles that then slam into the nearby material and push away the hot gas. “You’re literally seeing the impact the black hole is having,” says Julie Hlavacek-Larrondo of Stanford University in California. “And if you calculate the energy it takes to push away all that gas, it’s huge, it’s amazing. That’s when you see just how powerful black holes are.” While previous generations of X-ray satellites saw hints of the cavities in Perseus A, the active galaxy at the center of the Perseus cluster, it took Chandra’s detailed eye to see it in so many other examples. These cavities extend some 30,000 to 300,000 light-years from the central black holes that clear them. Astronomers also believe some of these bubbles “generate some kind of a shock, and then we see these beautiful waves propagate through the medium,” says Hlavacek-Larrondo. Perseus A illustrates these shock fronts better than most other galaxies that scientists have studied. In all of the examples they’ve analyzed, a black hole is creating structures at least a billion times larger than itself. It’s pumping a lot of energy into its environment, heating gas or pushing it away — and hindering star formation and thus galaxy growth. W W W.ASTR ONOM Y.CO M

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When you look at a galaxy cluster in visible light, you see hundreds or thousands of galaxies — made up of billions of stars each — in a huge conglomeration. But look at it with X-ray eyes, and you see the high-energy glow of hot gas between all those galaxies — a lot of it. In fact, in a cluster “the mass of the hot gas exceeds the mass in the galaxies by about a factor of seven,” says Richard Mushotzky of the University of Maryland, College Park. Yet even that normal matter is a small fraction of the cluster’s total mass. Another material, called dark matter, completes the picture. One way to “see” this mysterious, pervasive mass is by studying huge clusters of galaxies, which grow through the collisions and mergers of smaller clusters. The Bullet Cluster (1E 0657–55.8), the product of such a crash, is the most famous example. As two clusters merged, their gas

interacted via the electromagnetic force. The gas lost energy and slowed down relative to the galaxies and dark matter. Astronomers compared the X-ray observations, which Chandra collected in the early 2000s, to optical light that displays a trick of gravity. The enormous mass of the Bullet Cluster warps the light from galaxies behind the cluster from Earth’s viewpoint. “So the background galaxies are just slightly distorted and extended,” says Harvey Tananbaum, the man at the helm of Chandra until earlier this year, when he stepped down. “You don’t know exactly their shapes to begin with, but statistically you can average over a large enough number and back out where the clumps of mass should be.” When Maxim Markevitch, then at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and

NASA/CXC/S. KOMOSSA, ET AL.

4 In 2001, astronomers discovered the first case of binary gigantic black holes at a galaxy’s center. They think that two galaxies — each with its own supermassive black hole — collided to create NGC 6240.

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Pairs of monster black holes found

In 2001, while peering at the galaxy NGC 6240 with the Chandra X-ray Observatory, astronomers found that its center hosts two active giant black holes. This was the first image of a binary supermassive black hole system, and since then, astronomers have discovered a few dozen pairs. The nearest such binary system to Earth lies about 160 million light-years away in

The Chandra X-ray Observatory imaged the hot gas (shown as pink) within the Bullet Cluster (1E 0657–55.8), and scientists used a trick of gravity to determine the mass distribution in the object (blue). Because the normal matter peak and the cluster’s mass peak don’t line up, the cluster appears to hold invisible dark matter.

colleagues compared the two distributions, they found that the hot X-ray-emitting gas and most of the cluster’s mass did not line up. “The offset provides a direct proof that the total mass is dominated by something other than the visible matter,” says Markevitch, “that is, by dark matter.” The Bullet Cluster gave scientists another piece of evidence that dark matter exists. The team also was able to limit ideas of what dark matter is because of how little the mysterious invisible mass interacted with itself when the clusters merged. Clumps of dark matter passed right through one another.

the spiral NGC 3393. The black holes are 490 light-years from each other. These observations give astronomers even more evidence that galaxies coalesce and combine to form larger structures, and that even their central supermassive black holes eventually merge. In the examples found so far, several million years will pass before the two massive objects combine. As they near each other, they release gravitational radiation, which astronomers hope to directly see with future observatories equipped to detect such gravitational waves.

XRAY: NASA/CXC/CFA/M. MARKEVITCH, ET AL.; OPTICAL: NASA/STSCI; MAGELLAN/UNIV. OF ARIZONA/D. CLOWE, ET AL.; LENSING MAP: NASA/ STSCI/ESO WFI/MAGELLAN/UNIV. OF ARIZONA/D. CLOWE, ET AL.

3Giant galaxy clusters collide


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The Milky Way’s supermassive black hole varies

October 1999

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December 2002

Watching a young supernova remnant evolve

Since October 1999, the Chandra X-ray Observatory has followed the evolution of debris at the site of the February 1987 stellar explosion known as Supernova 1987. This blast occurred in the Large Magellanic Cloud, a satellite galaxy of the Milky Way; it was the nearest supernova to Earth in hundreds of years and has provided astronomers a laboratory to study how the leftover material changes and how it affects the diffuse interstellar medium.

July 2006

When astronomers trained the Chandra X-ray Observatory on the Milky Way’s core, they confirmed that the center hosts a supermassive black hole. They also spied X-ray flares, which occur once a day on average — but they don’t know what causes these bursts. NASA/CXC/MIT/F. K. BAGANOFF, ET AL./E. SLAWIK

March 2010

KARI FRANK AND DAVID BURROWS, PENN STATE

Just a few months after opening its eye, Chandra gave scientists the first definitive X-ray detection of the supermassive black hole that sits at the Milky Way’s center. The observatory also found a surprise: the black hole, called Sagittarius A* (pronounced “A-star”), flares, and now researchers know that these bursts occur once a day on average. But 14 years after discovering the first of these X-ray flares, astronomers still don’t know what’s causing them. “These flares could be small magnetic reconnection events that are going on and having this release of radiation just like we see on our Sun,” says Daryl Haggard of Northwestern University in Evanston, Illinois. “The competing theory that fits the population of flares is the shredding of little asteroids. Those two things fit the data pretty much equally well. We cannot distinguish between them, and they are not the same theory.” During the years of watching Sgr A* with Chandra, astronomers have spied other surprises as well. They’ve seen faint pulses of light, which they have learned arrived at Earth a few hundred years after larger radiation bursts. Some of the original blasts’ light bounced off debris near Sgr A* before heading to our planet. These signals took a slightly longer journey on their way to Earth, and thus we see them later. These “light echoes,” observed in just the past few years, suggest that the Milky Way’s central black hole was actively eating nearby material and spewing radiation within the past few hundred years. “The galactic center is extremely interesting and rich,” says Haggard, “and every time you go and look at it in the X-ray, something else pops its head up.”

September 2013

The nearest supernova to Earth in hundreds of years was Supernova 1987A. Scientists using Chandra have been observing how this astronomical laboratory evolves since shortly after the telescope’s launch, and they’ve been able to track how the stellar explosion’s shock front heats nearby material.

David Burrows of Pennsylvania State University and colleagues have observed SN 1987A roughly twice a year since October 1999. “What we found is that the shock wave from the supernova explosion has been heating up cold gas in the ‘inner ring’ of material around the explosion site,” he says. Observations from 1996 with the Hubble Space Telescope showed knots of material forming around the inner ring, and studies with Chandra reveal that some of the gas has been heated to temperatures of several million degrees — hot enough to emit X-rays. “Since our observations began,

the X-ray source has increased in brightness by nearly a factor of 50, and we have been able to measure the expansion of the X-ray emission as the shock wave moves into the surrounding gas,” Burrows says. “What is really tantalizing for the future is the possibility that the X-rays from the shock front may begin probing material we haven’t seen yet,” he adds. “It is possible that the ‘ring’ is really just the inner edge of an extended disk.” The astronomers will keep monitoring SN 1987A to see if it continues to brighten or instead fades. If it brightens, the ring is an edge; it if fades, it really is a ring. W W W.ASTR ONOM Y.CO M

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NASA/CXC/CHINESE ACADEMY OF SCIENCES/F. LU, ET AL.

Stripe patterns

Companion star’s shadow

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Structure seen in supernova remnants

When a massive star explodes, it does so in a hot jumbled mess. Astronomers, however, used to think these detonations were symmetrical. “With Chandra’s resolution, you can see exactly how complex and clumpy they are,” says Julie Hlavacek-Larrondo of Stanford University. “It’s not just a ball that’s exploding; there’s a lot of structure there.” The explosive star, called a supernova, reaches temperatures hot enough to fuse heavy elements. The blast ejects the hot element-rich material into space, and this debris becomes a supernova remnant, a painted tapestry that reveals the blast’s dynamics. Gas that glows at millions of degrees — like that associated with a supernova — emits X-rays. And each chemical element gives off specific wavelengths (or colors) of light when heated. Astronomers collect the supernova remnant’s light and break it apart into its constituent wavelengths to determine which elements within the object are glowing. Using Chandra, researchers have mapped oxygen, silicon, sulfur, magnesium, iron, and other materials.

The angular resolution of the Chandra X-ray Observatory has revealed details never before seen in the debris left over after a stellar explosion. In the Tycho supernova remnant, astronomers found striped patterns that result from tangled magnetic fields and evidence of a companion star blocking the supernova’s material.

As it turns out, those elements are not distributed symmetrically in the remnant. For example, Cassiopeia A has two plumes rich in silicon extending outward toward opposite sides of the remnant. Astronomers also can watch how the supernova’s material interacts with the diffuse interstellar medium. As the dying star’s gas rams into the surrounding material, the impact site heats up and glows in X-rays. Chandra’s resolution allows scientists to see the shock fronts from the collision. In Tycho’s supernova remnant, astronomers found stripes, which result from electrons spiraling around tangled magnetic field lines near the debris’ outgoing shock wave. Sometimes astronomers can combine many observations of a supernova remnant to trace the expansion back in time and figure out if the exploded star had a partner that it fed off. In one such study of Tycho’s remnant, they detected a “shadow” that resulted from a companion star blocking some of the supernova’s material. All of these observations give researchers details about stellar death, which helps them piece together Liz Kruesi is an associate editor of Astronomy. how the original stars lived. 28

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Scientists detected high-energy radiation emanating from all directions, but they couldn’t pin down the source of these X-rays until Chandra launched. It turns out that a plethora of active galaxies spews large amounts of X-ray emission. Each of the points in this deep-field image marks one such galaxy. NASA/GSFC MUSHOTZKY, ET AL.

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Active galactic nuclei are prolific

In 1962, astronomers detected uniform X-ray signals across the sky, which they thought resulted from either a huge amount of hot gas spread throughout the cosmos or a bunch of individual point sources. Decades of X-ray observations did resolve more and more energetic sources, essentially ruling out a diffuse X-ray background of hot gas. However, these known sources, like the centers of active galaxies that spew radiation, still accounted for just 20 percent of the overall signal scientists detected. Then came Chandra and its ability to see finer details. In late 1999, Richard Mushotzky of the University of Maryland and colleagues imaged the location of an expected galaxy cluster. (Previous observations indicated the object was there.) “Lo and behold, my cluster wasn’t there,” he says. “But there were all these point sources. They turned out to be rather distant active galactic nuclei. And then we did some simple arithmetic. We were able to account for more than 80 percent of the X-ray background.” With that 28-hour observation, Mushotzky’s group figured out the answer and met one of Chandra’s main science goals. They found 36 active galaxies in that image, and from those objects, they could account for most of the overall X-ray radiation. Daryl Haggard of Northwestern University sums up the discovery: “We hadn’t previously known just how many black holes were hiding out there. And it turns out all those hidden black holes were throwing tons of X-ray photons out into the universe and creating this X-ray background.”


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A black hole’s speedy wind

The stellar-mass black hole IGR J17091–3624 is stealing material from its companion star and funneling that gas into a disk surrounding the black hole, as shown in this illustration. Astronomers studied the pair with the Chandra X-ray Observatory and discovered that the disk is blowing a wind at some 3 percent light-speed. That’s nearly 10 times faster than any such wind ever seen before. NASA/CXC/M. WEISS

A black hole of about 10 solar masses (with the friendly name of IGR J17091–3624) and its stellar companion are locked in a gravitational dance. The star is blowing away its outer layers of gas, which the black hole is happily grabbing. That material forms an accretion disk around the black hole, which glows hot and emits ultraviolet radiation. Interactions cause the nearby material to glow in X-rays, allowing Chandra to see it and X-ray astronomers to analyze the region. In addition to taking pictures of objects, Chandra collects information about the specific wavelengths of emitted radiation. By

10 The Orion Nebula (M42) hosts thousands of forming stars. Astronomers using the Chandra X-ray Observatory found 28 Sun-like stars between 1 million and 10 million years old that experience much more intense X-ray flares than the Sun. These high-energy outbursts would affect the surrounding disks of gas and dust that eventually form planets. XRAY: NASA/CXC/PENN STATE/E. FEIGELSON & K. GETMAN, ET AL.; OPTICAL: NASA/ESA/STSCI/M. ROBBERTO, ET AL.

watching how those wavelengths shift, scientists learn about the material’s movement. In 2011, Ashley King, then at the University of Michigan in Ann Arbor, and colleagues studied the wavelengths from IGR J17091–3624 to find that its disk blows a wind 10 times speedier than ever seen coming from an accretion disk surrounding a stellar-mass black hole. The wind moves at 3 percent light-speed. The scientists then compared these observations with data obtained just a couple months prior to find that the black hole system didn’t have a speedy wind previously. This means that such features can change on quick time frames, astronomically speaking.

Young Sun-like stars flare … a lot

Using Chandra’s X-ray vision, astronomers have probed high-energy activity on young Sun-like stars, giving them hints about our Sun’s youth. In 2003, astronomers peered at the Orion Nebula (M42) for nearly 13 days. Of the more than 1,000 stars detected, 28 of them spew blasts of X-rays. The scientists determined that these stars are between 1 million and 10 million years old. Such outbursts are much more energetic than anything our 4.6-billion-year-old Sun experiences, and scientists want to know how they affect planet growth. Astronomers can combine what they learn through X-ray observations with other types of radiation. For example, infrared vision shows clouds of dust and gas around stars — disks of material that will form into planets. Researchers also can estimate the masses of those stars from the

infrared radiation. Because young stars are brighter X-ray sources, scientists can compare their ages and masses and if they have surrounding disks. It turns out that the disks surrounding stars five to 10 times as massive as the Sun disappear within a few million years, but those around stars more like the Sun last longer. “So if you’re going to form giant planets like Jupiter, then you need a disk to do that, and they have to form pretty quickly,” says Harvey Tananbaum of the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts. “Combining the X-ray and the infrared data, we begin to get a handle on the lifetime of disks around stars of different masses.” Such research gives scientists hints of how the disk of gas and dust surrounding our young star formed into eight major planets and uncountable smaller bodies.

LEARN ABOUT A FEW MORE IMPORTANT CHANDRA DISCOVERIES AT www.Astronomy.com/toc. W W W.ASTR ONOM Y.CO M

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X-treme energies

NuSTAR can see X-rays more extreme than any other telescope, opening a new window on the oldest black holes and the newest supernovae. by Michael E. Bakich 30

A ST R O N O M Y • JULY 2014


or thousands of years, skywatchers used only their eyes to survey our universe. Although tremendously useful to us, these detectors collect only one type of electromagnetic radiation: visible light. It took a long time for humans to venture outside this limited range of wavelengths. Finally, in 1800, German-born English astronomer William Herschel discovered infrared radiation, and the following year German physicist Johann Wilhelm Ritter observed the effect of ultraviolet rays. Then followed microwaves (1864), radio waves (1887), X-rays (1895), and gamma rays (1900). Each time a new region of the spectrum opened, discoveries followed. During the intervening century, astronomers have studied all forms of radiation, but they have had problems obtaining clear views through the window defined by high-energy X-rays. Researchers quantify the energy of radiation by using a unit called the electron volt (eV). Visible light has an energy range of 1.6 eV to 3.4 eV. But high-energy X-rays are, as the name suggests, much more energetic. Their range is from 3 keV to 79 keV, where the k signifies “thousand.” And these “hard” X-rays are the Nuclear Spectroscopic Telescope Array’s (NuSTAR) specialty.

A new approach

The NuSTAR X-ray telescope orbits Earth, catching the high-energy X-rays from the universe’s most distant objects. NuSTAR: NASA/JPL

Our atmosphere absorbs this piercing radiation (lucky for us!), so researchers through the years have used high-altitude balloons, sounding rockets, and now satellites to rise above the layer of air that surrounds our world. NuSTAR is a space-based telescope whose predecessors include the Einstein Observatory, launched in 1978, ROSAT (1990), the Chandra X-ray Observatory (1999), and XMM-Newton (1999). But the detectors in these telescopes were made to detect energies between 0.1 keV and 10 keV. The few satellites that collected higherenergy X-rays produced considerable background interference and were not sensitive. Despite the clear need for a telescope that could collect hard X-ray data, NuSTAR almost didn’t happen. While NASA approved the project in 2005, the agency canceled the mission a year later due to budget cuts. Luckily, NuSTAR’s champions

CALTECH; EARTH: NASA

Michael E. Bakich is a senior editor of Astronomy. W W W.ASTR ONOM Y.CO M

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Shielded focal plane detectors

NuSTAR: An anatomical guide

B Focal plane bench Deployed mast

Path of X-rays

plane B Focal detector X-rays Focal surface Optics modules

A A

Hyperboloid reflector

Inside the optics module Paraboloid reflector

NuSTAR consists of two main elements connected by a mast, which engineers deployed after the telescope was already in orbit. The optics modules capture X-ray photons and focus them onto the focal plane bench, where instruments turn them into digital signals. The focusing optics guide the photons along a shallow-angle path. ASTRONOMY: ROEN KELLY, AFTER NASA/JPLCALTECH

convinced NASA to flip-flop again. “The best experience was making the case to NASA to reinstate us and having NASA do it,” says says Fiona Harrison of the California Institute of Technology in Pasadena and NuSTAR’s principal investigator. That happened in September 2007. In mid-2012, NuSTAR finally made it into space. NASA contracted with Orbital Sciences Corporation of Dulles, Virginia, the firm that also built the spacecraft. Engineers affixed the 790pound (360 kilograms) craft to a Pegasus XL rocket, and, on June 13, 2012, the Stargazer (a modified Lockheed L-1011 aircraft owned by Orbital Sciences) dropped the duo above the Pacific Ocean some 2,000 miles (3,200 kilometers) southwest of Hawaii. From there, the rocket carried the telescope into space. Now, a dozen teams of scientists and engineers peer through NuSTAR’s window.

A new design NuSTAR consists of two co-aligned Wolter telescopes, also known as grazing incidence telescopes. Because normal mirrors either absorb or are transparent to X-rays, these instruments have specially

coated focusing optics tilted at no more than 2° to incoming radiation. The X-rays, then, glance off the reflectors at shallow angles. Each optics set, with focal lengths of 33.3 feet (10.2 meters), sits at the end of a long mast deployed once the satellite achieved orbit. In addition to the small angles of reflection required to focus X-rays, such a design also requires special materials. Past missions used dense elements like gold and platinum as coatings, but they don’t work as well for high-energy X-rays. So, for NuSTAR, engineers coated the segments with 400 ultra-thin layers, alternating between high-density (platinum and tungsten) and low-density (silicon and silicon carbide) materials. The result is an observatory that provides higher sensitivity and 10 times better resolution than previous missions that operated at these X-ray energies. Each focusing optic is actually a set of 130 concentric shells built from the inside out. Engineers placed graphite spacers between the shells and held the assemblies together with epoxy. The 65 inner shells each have six reflective segments, while the 65 outer shells contain 12. NuSTAR’s primary mission lasts just two years, but NASA likely will extend funding. Scientists will use it to investigate the invisible

Not all X-rays are created equal Wavelength (meters) 10 – 7

Visible 10eV light Energy (electron volts [eV])

10 –8

10 2

10 –9

1keV Chandra 0.1–10 keV

10–10

10 4

10 –11

10 5

10 –12

1MeV

NuSTAR 3–79 keV

Astronomers classify X-rays as either soft (lower energy) or hard (higher energy). Prior to NuSTAR, most telescopes specialized in the soft variety, which means NuSTAR is plumbing new depths, electromagnetically. ASTRONOMY: ROEN KELLY

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Visible-light dots in the night sky are usually stars. Dots that NuSTAR sees, however, are active black holes bedded down in the centers of distant galaxies. The Chandra X-ray Observatory previously detected black holes in red and green, which have lower energies than the blue black holes, which NuSTAR saw. NASA/JPLCALTECH/YALE

Spiral galaxy IC 342 has at least two dark secrets. The Chandra X-ray Observatory detected two intermediate-mass black holes, whose X-rays are shown in magenta, in its spiral arms. Because such medium-sized black holes are still mysterious, scientists plan to use NuSTAR to detect and study many more of them. NASA/JPLCALTECH/DSS

energetic universe — specifically astronomy fan-favorites like black holes, blazars, and supernovae, where the action and the X-rays are.

rotation rate. Black holes have masses that range from stellar — a few times that of the Sun — to supermassive — millions or billions of times the Sun’s mass. Scientists also use the telescope to hunt black holes in other galaxies. Their highest priority is to survey areas where researchers have found visible and infrared counterparts — objects that other telescopes have found whose locations match up with those of X-ray sources. X-rays don’t tell scientists much about the nature of celestial sources, but other wavelengths, like visible light, do.

Sizing up black holes

One of NuSTAR’s first orders of business is to check out the core of the Milky Way. Telescopes that collect visible light cannot penetrate the clouds of gas and dusty regions that lie near the galaxy’s center. Luckily, high-energy X-rays have no trouble at all passing through this material, and NuSTAR looks for them. Astronomers point NuSTAR toward — but not directly at — the Ultra-weird heart of the Milky Way, which contains a supermassive black hole. Astronomers have to look outside the galaxy to unearth the secrets Known as Sagittarius A* (pronounced “A-star”), it contains about of a mysterious type of object called an ultraluminous X-ray source 4 million solar masses. (ULX), first discovered in the 1980s. They are brighter in X-rays Previous X-ray telescopes have revealed many sources in that than scientists expect any star or stellar-mass black hole to be, but region besides the black hole, so this is a fertile hunting ground for stellar-mass black holes and other equally strange objects. Astrono- they are dimmer than active supermassive black holes, leaving astronomers shrugging and then pointmers want to know how many black holes ing their telescopes to distant space. Sev(not counting the supermassive one at eral theories are afloat as to what ULXs our galaxy’s center) populate the region. are, but none provokes more discussion When a massive star explodes as a than the possibility they are a new class supernova, its core may collapse into an of black hole. ultra-dense object that astronomers call a Currently, astronomers recognize black hole. The object is “black” because stellar-mass and supermassive black its gravity is so strong that not even light holes, and new discoveries suggest a can escape. middle ground exists: An intermediateA black hole swallows anything that mass class of black hole that dwarfs the comes within a gravitational boundary stellar variety but is, in turn, dwarfed by called the event horizon. Just outside that the monsters in the hearts of galaxies. frontier, a swirling accretion disk of Although astronomers know these sizeintensely hot matter forms. This disk medium objects are out there, they don’t causes X-ray emission that tips scientists Astronomers do not know why ultraluminous X-ray sources (ULXs), such as those shown in NGC know much about how they came to be. off to the presence of a black hole — 1313 (magenta), shine so brightly. They do know, “Exactly how intermediate-sized which researchers cannot see directly. however, that ULXs are black holes in the process black holes would form remains an open Once astronomers find a black hole, of consuming material and that their meals fuel issue,” said Dominic Walton of the the next step is to determine its mass and their high-energy emissions. NASA/JPLCALTECH/IRAP W W W.ASTR ONOM Y.CO M

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And it really doesn’t matter that the supermassive black holes lie hidden behind thick walls of material. “Our early results show that the more distant supermassive black holes are encased in bigger galaxies,” Daniel Stern, a co-author of the study and the project scientist for NuSTAR at NASA’s Jet Propulsion Laboratory in Pasadena, California, said in September. “This is to be expected. Back when the universe was younger, there was a lot more action with bigger galaxies colliding, merging, and growing.”

Scrutinizing blazars

California Institute of Technology in Pasadena last November. “Some theories suggest they could form in dense clusters of stars through repeated mergers, but there are a lot of questions left to be answered.” Walton and his colleagues recently used NuSTAR to study one possible candidate, ESO 97–G13, which lies 13 million light-years away in the Circinus Galaxy, one of the closest active galaxies to the Milky Way. They also incorporated archival data from other space telescopes. “We went to town on this object, looking at a range of epochs and wavelengths,” Walton said. His team found that ESO 97–G13 contains approximately 100 times as much mass as the Sun. If that finding holds, it means the source is either an incredibly massive stellar black hole or at the lower end of the intermediate-mass range.

Explosive mapping In addition to learning about such large-scale violence, NuSTAR can zoom in on small stuff, like supernovae. Since early cosmic

Which way does it go? Retrograde spin

Black hole

Counting black holes

X-ray brightness

No spin

Energy

Prograde spin

Energy

NuSTAR looks at the illuminated material around black holes. From those X-rays, astronomers can determine how the invisible black holes are spinning. A black hole’s X-ray spectrum has different slopes, peaks, and valleys depending on whether it has retrograde rotation (meaning the disk of matter spins opposite the black hole), prograde rotation (where disk and hole spin the same direction), or no spin. ASTRONOMY: ROEN KELLY, AFTER NASA/JPLCALTECH

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A ST R O N O M Y • JULY 2014

Energy

Accretion disk

X-ray brightness

NuSTAR can find black holes of all sizes, though. After the space telescope found its first 10 supermassive black holes, David Alexander, a NuSTAR team member based at Durham University in England, said last September, “We found the black holes serendipitously. We were looking at known targets and spotted the black holes in the background of the images.” The researchers discovered that other X-ray satellites had detected them, but it wasn’t until the NuSTAR observations that the black holes looked interesting enough for follow-up. These objects, and others that NuSTAR will find, will help astronomers estimate how many black holes the universe contains. “We are getting closer to solving a mystery that began in 1962,” Alexander continued. “Back then, astronomers had noted a diffuse X-ray glow in the background of our sky but were unsure of its origin. Now, we know that distant supermassive black holes are sources of this light, but we need NuSTAR to help further detect and understand the black hole populations.” That’s because the cosmic X-ray background, the term that astronomers use to refer to this glow, is right in NuSTAR’s wavelength “sweet spot.”

X-ray brightness

The center of the Milky Way, just like the centers of other galaxies, hosts a supermassive black hole (Sagittarius A*). It is calmer than many others — and much calmer than NuSTAR’s normal targets — but because it’s nearby, scientists can observe its occasional flare-ups. This one, which occurred in July 2013, shows Sagittarius A* before the flare’s peak (top), during the peak (middle), and as the flare faded (bottom). At the height of its hype, the black hole heated matter up to 180 million degrees Fahrenheit (100 million degrees Celsius). NASA/JPLCALTECH

The most energetic of these active galaxies launch plasma from their poles at near the speed of light. Astronomers believe these jets originate from the supermassive black holes in the cores of galaxies. Sometimes a black hole’s jets align with the accretion disk’s rotation axis. Of course, the jets could point toward any location in space, but they appear brightest to telescopes like NuSTAR if Earth is in the jets’ line of sight. Astronomers call such aligned sources blazars. Occasionally, something perturbs the vast amounts of dust and cold gas that surround a galaxy’s core. The black hole’s gravity captures this material, which falls into the ultra-dense object, causing radiation outbursts. Even though such flares come from billions of light-years away, they stand out to NuSTAR’s detectors. The telescope’s sensitivity allows it to probe the high-energy X-ray emissions of blazars with the best resolution so far, which astronomers hope will reveal how the jets form and operate.


NuSTAR scientists hope to catch cosmic rays, particles traveling at near lightspeed, as they’re being accelerated. Last year, astronomers discovered that supernova remnants, like Cassiopeia A, give some particles their speed boosts. As they repeatedly cross the leading edge of the remnant’s shock wave (blue), their velocities increase. NASA/JPLCALTECH/DSS

Astronomers had aimed NuSTAR at IC 751 (right, magenta) when they accidentally discovered another X-ray-active supermassive black hole (left, magenta). Learning about the interactions between supermassive black holes and their hosts allows astronomers to understand how galaxies like the Milky Way form and evolve. NASA/JPLCALTECH

history, the universe’s contents have been going through cosmic recy- The Sun, too? One of NuSTAR’s targets lies billions of times closer than even galaccling. Stars form and evolve; the most massive ones then blow themtic supernovae. It’s the Sun’s corona, a region of thin, multimillionselves to bits, releasing the heavy elements built up in their cores. degree plasma that surrounds the more substantial sphere of our star. Material from those stars finds its way into uncounted star-forming Normally invisible (except during the total phase of a solar eclipse), it regions, so new stars that form contain heavy elements from birth. Astronomers want to study the elements, even short-lived ones, is an active region where loops of plasma extending from the surface, the sudden brightening of solar flares, and the resulting mass ejecthat result from supernovae. By doing so, they’ll find out what conditions — like temperature, pressure, and composition — ruled tions of hot plasma often intrude. Solar physicists studying this envelope want to answer one question: Why is the corona so hot? within the cores of the massive stars that exploded. Some researchers think the mechaIn February, the NuSTAR team nism that heats the corona involves a high reported that it had created the first map number of miniature solar flares called of one such element, titanium-44, in a nanoflares. NuSTAR is the instrument of supernova remnant called Cassiopeia A, choice to study them because nanoflares which astronomers first detected as a radio produce high-energy X-rays. source in 1947. The map showed a nonTo find out if that hunch is correct, uniform distribution of titanium that proastronomers primarily aim the telescope vided a clue as to why such stars explode. at the Sun’s active regions, areas of strong “Stars are spherical balls of gas, and so magnetic fields usually associated with you might think that when they end their sunspots. For a more general study, they lives and explode, that explosion would also can pinpoint normal flares occurring look like a uniform ball expanding out all over the Sun’s surface. with great power,” Harrison said in FebruStudying objects ranging from our ary. “Our new results show how the explohometown star to the most distant, most sion’s heart, or engine, is distorted, extreme galaxies, NuSTAR covers the possibly because the inner regions literally scope and scale of the universe in a way slosh around before detonating.” that no one has ever seen before. If recent The more NuSTAR helps scientists history teaches us anything, it’s that openlearn about how stars explode, the more After a massive star explodes, its condensed leftover core can become a pulsar — a beacon-emitting ing a new window on the cosmos leads to they will learn about why the universe has neutron star. Pulsar B1509 slings a particle wind into wonderful and unexpected discoveries. the composition it does and how that parthe cast-off stellar material, creating a pulsar wind It’s a safe bet, then, that the revelations ticular composition leads to the different nebula. This image from NuSTAR shows its wind that come from NuSTAR will influence types of stars and planets that exist across nebula called the “Hand of God.” NASA/JPLCALTECH/M GILL astronomers for a generation to come. the universe. C

WATCH A VIDEO OF NUSTAR’S TRIP TO SPACE AND A SIMULATION OF A SUPERNOVA EXPLOSION AT www.Astronomy.com/toc. W W W.ASTR ONOM Y.CO M

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SKYTHIS MONTH

Visible to the naked eye Visible with binoculars Visible with a telescope

MARTIN RATCLIFFE and ALISTER LING describe the

solar system’s changing landscape as it appears in Earth’s sky.

July 2014: Pluto comes to the fore

A

Saturn

Mars

Spica

A waxing crescent Moon anchored the early evening sky August 21, 2012. Mars stood above and a little left of Luna while Saturn appeared at the scene’s upper right with Spica directly below it. The same objects (minus the Moon) gather in mid-July this year. ALAN DYER

Mars meets Spica at dusk Arcturus OPHIUCHUS

Antares

LIBR A

SC OR PIUS

LUPUS

Saturn

VIRGO

Mars Spica

CENTAURUS

Denebola

10°

C ORVUS

July 12, 10 P.M. Looking southwest Notice the color contrast between Mars and Spica when the Red Planet slides 1.4° north of the blue-white star the evening of July 12. ASTRONOMY: ROEN KELLY

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A ST R O N O M Y • JULY 2014

lthough summer nights are short, they still pack quite a wallop. Evening observers this July can enjoy wonderful views of Mars and Saturn, which offer a nice contrast in both color and telescopic appearance. The outermost planets, Uranus and Neptune, take center stage after midnight. Patient viewers at dark sites can spot these ice giant worlds easily through binoculars. This month’s morning sky hosts Mercury and Venus. The two inner worlds shine brightly low in the east before sunrise. At the opposite end of the brightness scale, Pluto reaches its peak in July. You’ll likely need an 8-inch or larger telescope to spot this 14thmagnitude object visually. Fortunately, it lies in a part of northern Sagittarius that contains a couple of bright stars to guide you to the right spot. Our tour of the solar system begins shortly after sunset in early July. On the 1st, Jupiter hangs 5° above the west-northwestern horizon 30 minutes after sunset. It shines brightly at magnitude –1.8, which is why it shows up despite the low altitude. The giant planet disappears after July’s first few evenings and passes behind the Sun from our perspective on the 24th. Mars appears in the southwest as darkness falls all month. On July 1, it stands 5.5°

Martin Ratcliffe provides planetarium development for Sky-Skan, Inc., from his home in Wichita, Kansas. Meteorologist Alister Ling works for Environment Canada in Edmonton, Alberta.

northwest of Spica, the brightest star in Virgo the Maiden. The planet shines at magnitude 0.0, a full magnitude brighter (equivalent to a factor of 2.5) than the star. Mars’ orange glow contrasts nicely with Spica’s blue-white hue. If you watch every clear evening in early July, you’ll notice these two objects are pulling closer to each other. On the 5th, a First Quarter Moon jumps between the pair. Across North and South America, our satellite appears within 1° of Mars. Observers in Central America and the northern half of South America will see the Moon pass directly in front of the planet and block it from view. Mars’ eastward motion relative to the background stars continues throughout July. On the 12th, the Red Planet passes 1.4° north of Spica. The pretty conjunction will look best through binoculars or a telescope at low power. By month’s end, Mars has pulled 9° east of the star. Although Mars remains visible until midnight local daylight time or later during July, the best views through a telescope come when it lies highest as soon as darkness falls. The planet shows a distinct phase, particularly around quadrature July 19. (At this configuration, the SunEarth-Mars angle equals 90° and the phase effect is greatest.) The planet’s 9"-diameter disk should display a few dark surface markings during moments of good seeing, when Earth’s atmosphere steadies and the view sharpens. Saturn lies a short hop east of Mars among the stars


RISINGMOON An ancient blast mars a tranquil spot Mare Tranquillitatis — the Sea of Tranquility — wasn’t always calm and peaceful. A giant impact created this basin billions of years ago. Millions of years after that, lava erupted through cracks in the floor. The fractures tend to lie along stress lines created by earlier impacts that formed other large basins. A second round of upwelling lava caused the terrain to heave unevenly, producing cliffs (scarps); in other places, lava tubes collapsed into narrow depressions known as rilles. Nearby, some volcanoes pushed toward the surface, creating symmetric hills called “domes.” Three days after New Moon, on the evening of July 1, the Sun rises on a fascinating area of Mare Tranquillitatis surrounding Cauchy Crater. The region lies

of Libra the Balance. The separation between the two planets drops from 28° to 12° during July. The shrinking gap heralds an upcoming close approach — the two will pass 4° from each other in late August. This month, you’ll find the ringed world about 30° high in the southwest as twilight fades. Shining at magnitude 0.4, Saturn appears more than two magnitudes brighter than any of Libra’s suns. The nearest 1st-magnitude star is Scorpius’ luminary, Antares, which stands to the planet’s lower left. Notice the contrast between yellowish Saturn and the orange hue of the red supergiant star. Swing your telescope toward Saturn, and marvel at the golden globe encircled by a spectacular ring system. The planet’s disk measures 18" across the equator while the — Continued on page 42

along the terminator — the line that divides day from night on the Moon — just north of the lunar equator. The crater itself is an 8-milewide impact feature with sharp edges, a sign of its relative youth. Immediately north of the crater appears the prominent rille Rima Cauchy. Years of tiny impacts have softened its edges. By July 3, the Sun has climbed higher in the lunar sky and shines directly into the rille, wiping out the shadows and making it all but invisible. Parallel to the rille and just south of the crater lies Rupes Cauchy. Many Moon observers consider this prominent scarp second only to the famous Straight Wall (Rupes Recta). At lunar sunrise, the scarp casts a sharp shadow westward, but

Cauchy Crater and its parallel companions Rima Cauchy Cauchy

Rupes Cauchy N

τ

ω

E

Although barely 8 miles across, Cauchy Crater stands out on a waxing crescent Moon. A prominent rille (Rima Cauchy) and scarp (Rupes Cauchy) sandwich the crater. CONSOLIDATED LUNAR ATLAS/UA/LPL; INSET: NASA/GSFC/ASU

the dark line disappears a couple of days later. A real bonus in this region is a pair of lava domes. Look for two small hills protruding into the sunlight. The eastern dome is cataloged as Omega (ω) and the western one as Tau (τ). Return to this region again the night of July 15/16 (the

Moon rises before midnight local daylight time) when sunlight shines from the opposite direction. The scarp’s dark line has been replaced by a white streak sitting in the setting Sun’s glare. The monthly cycle almost repeats July 31, but the Sun is then a few hours higher in the Cauchy region’s sky.

METEORWATCH Fiery streaks from a watery constellation July is a fine month for meteor observing, particularly late in the month as the Moon shifts out of the morning sky, the nights grow longer, and the weather remains balmy. The best meteor shower is the Southern Delta Aquariids. Although it doesn’t produce a ton of “shooting stars” — you can expect to see 15 to 20 per hour at maximum — it maintains peak intensity for a few days. The greatest numbers rain down in the hour or two before morning twilight begins July 29 and 30. The meteors appear to radiate from a point near the star Delta (δ) Aquarii. This area climbs reasonably high before dawn, particularly for observers at more southerly locations.

OBSERVING HIGHLIGHT

Southern Delta Aquariid meteors Active Dates: July 12–Aug. 23 Peak: July 30 Moon at peak: Waxing crescent Maximum rate at peak: 16 meteors/hour

Southern Delta Aquariid meteor shower

Enif

PISCES

DELPHINUS AQUARIUS CETUS

Radiant Fomalhaut

CAPRIC ORNUS

GRUS

10°

July 30, 4 A.M. Looking south With the Moon gone from the morning sky in late July, conditions should be ideal for this shower’s peak. ASTRONOMY: ROEN KELLY

Asteroids Ceres and Vesta appear closer together in early July than at any time since they were discovered more than 200 years ago. W W W.ASTR ONOM Y.CO M

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N

STAR DOME NG

C8

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How to use this map: This map portrays the sky as seen near 35° north latitude. Located inside the border are the cardinal directions and their intermediate points. To find stars, hold the map overhead and orient it so one of the labels matches NE the direction you’re facing. The stars above the map’s horizon now match what’s in the sky.

C8

ALIS

69

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M8

M82

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midnight July 1 11 P.M. July 15 10 P.M. July 31

URSA MINOR

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The all-sky map shows how the sky looks at:

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A star’s color depends on its surface temperature.

• • • • • •

The hottest stars shine blue Slightly cooler stars appear white

SE

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The coolest stars glow red Fainter stars can’t excite our eyes’ color receptors, so they appear white unless you use optical aid to gather more light

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M4

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Intermediate stars (like the Sun) glow yellow Lower-temperature stars appear orange

res Anta

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TELES

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1 NGC 623


Note: Moon phases in the calendar vary in size due to the distance from Earth and are shown at 0h Universal Time.

JULY 2014 SUN.

MON.

TUES.

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THURS.

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MAP SYMBOLS Open cluster Globular cluster Diffuse nebula 6

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Calendar of events

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ILLUSTRATIONS BY ASTRONOMY: ROEN KELLY

Galaxy

1 Mercury is stationary, 10 A.M. EDT

13 The Moon is at perigee (222,612 miles from Earth), 4:26 A.M. EDT

2 Venus passes 4° north of Aldebaran, 6 A.M. EDT

15 The Moon passes 5° north of Neptune, 1 P.M. EDT

3 Earth is at aphelion (94.5 million 18 The Moon passes 1.4° north of miles from the Sun), 8 P.M. EDT Uranus, 6 A.M. EDT SPECIAL OBSERVING DATE 4 Pluto reaches opposition and peak visibility this morning, when it glows at magnitude 14.1 among the background stars of northern Sagittarius. 5

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YD

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First Quarter Moon occurs at 7:59 A.M. EDT

Full Moon occurs at 7:25 A.M. EDT Mercury is at greatest western elongation (21°), 2 P.M. EDT

SW UP

21 Saturn is stationary, 11 A.M. EDT 22 Uranus is stationary, 5 A.M. EDT 24 The Moon passes 4° south of Venus, 2 P.M. EDT Jupiter is in conjunction with the Sun, 5 P.M. EDT

The Moon passes 0.2° north of Mars, 9 P.M. EDT

s

Pa

th

Last Quarter Moon occurs at 10:08 P.M. EDT

26

New Moon occurs at 6:42 P.M. EDT

27 The Moon is at apogee (252,629 miles from Earth), 11:28 P.M. EDT 29 Mercury passes 6° south of Pollux, 1 A.M. EDT 30 Southern Delta Aquariid meteor shower peaks

Mars passes 1.4° north of Spica, 7 P.M. EDT

US

BEGINNERS: WATCH A VIDEO ABOUT HOW TO READ A STAR CHART AT www.Astronomy.com/starchart. W W W.ASTR ONOM Y.CO M

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PATH OF THE PLANETS

The planets in July 2014 DR A

Objects visible before dawn LY N AND AUR

Mercury appears in G Ebright M the morning sky in mid-July C NC Sun

L AC

LYR

CYG

PER

H

TRI ARI

Venus

VUL PEG

Mercury

DEL OR I TAU

Victoria

Hebe

CMi

SGE

EQU

PSC

AQL

Uranus

Pat h of th

MON

O

Celestial equator

e Su

CET

AQR

n (e

clip ti

c)

SCT Path o f the Moo n

Psyche

Neptune

SE R

CMa LEP PYX

ERI FOR

C OL

PUP

CAE

27

for the year in early July Amphitrite

Comet LINEAR (C/2012 X1)

GRU

MIC

Dawn

Moon phases

28

Pluto appears at its best CAP SGR

PsA

SCL

26

25

Midnight

24

23

22

21

20

19

18

17

16

15

14

13

12

To locate the Moon in the sky, draw a line from the phase shown for the day straight up to the curved blue line. Note: Moons vary in size due to the distance from Earth and are shown at 0h Universal Time.

The planets in the sky

These illustrations show the size, phase, and orientation of each planet and the two brightest dwarf planets for the dates in the data table at bottom. South is at the top to match the view through a telescope.

Mercury

Uranus Mars

S W

E

Saturn Ceres

N

Venus

Neptune

Planets

40

Pluto

Jupiter

10"

MERCURY

VENUS

MARS

CERES

JUPITER

SATURN

URANUS

NEPTUNE

PLUTO

Date

July 15

July 15

July 15

July 15

July 1

July 15

July 15

July 15

July 15

Magnitude

0.0

–3.8

0.2

8.6

–1.8

0.4

5.8

7.8

14.1

Angular size

7.5"

11.4"

8.7"

0.5"

31.7"

17.6"

3.5"

2.3"

0.1"

Illumination

43%

89%

87%

96%

100%

100%

100%

100%

100%

Distance (AU) from Earth

0.902

1.467

1.080

2.467

6.219

9.462

19.889

29.244

31.688

Distance (AU) from Sun

0.363

0.723

1.509

2.691

5.258

9.922

20.020

29.974

32.688

Right ascension (2000.0)

6h07.1m

5h40.4m

13h28.7m

13h37.3m

7h54.0m

14h58.7m

1h01.1m

22h36.3m

18h50.4m

Declination (2000.0)

21°08'

22°31'

–10°07'

–3°04'

21°14'

–14°33'

5°47'

–9°36'

–20°20'

A ST R O N O M Y • JULY 2014

11


This map unfolds the entire night sky from sunset (at right) until sunrise (at left). Arrows and colored dots show motions and locations of solar system objects during the month.

UM A

Jupiter’s moons

Objects visible in the evening LY N

Dots display positions of Galilean satellites at 11 P.M. EDT on the date shown. South is at the top to match S the view E through a W N telescope.

CVn

HE R

LMi GEM

BOÖ

CrB

C OM

Comet PANSTARRS (C/2012 K1)

Jupiter Sun

LEO SE R

Vesta passes 0.2° south of Ceres on July 6

Pallas

OPH

MON

3

Saturn C RV

C RT

4

HYA CM a

Mars passes 1.4° north of Spica on July 12

5

ANT PYX

SCO

Callisto

2

SEX

LIB

M

Ganymede

1

CMi

Ceres ars

Europa

CNC

VI R

Vesta

Io

LUP

6

PUP 7

V EL

8

Early evening

Jupiter

9

Io

10

9

8

7

6

5

4

3

31

2

30

1

29

11

28

27

26

25

12 13

Callisto

Ganymede

14 15

Jupiter

16

Europa

17

Venus

18 19

Mercury Greatest western elongation is July 12

20 21

Mars Ceres

22

Earth Aphelion is July 3

23

25 26

The planets in their orbits Arrows show the inner planets’ monthly motions and dots depict the outer planets’ positions at midmonth from high above their orbits.

24

Jupiter Solar conjunction is July 24

27

ILLUSTRATIONS BY ASTRONOMY: ROEN KELLY

10

Uranus 28

Saturn

29

Neptune 30

Pluto Opposition is July 4

31

W W W.ASTR ONOM Y.CO M

41


— Continued from page 37

WHEN TO VIEW THE PLANETS EVENING SKY

MIDNIGHT

Mars (southwest) Jupiter (northwest) Saturn (south)

Mars (west) Saturn (southwest) Neptune (southeast)

rings span 40" and tilt 21° to our line of sight. Look for the shadow of Saturn’s orb falling on the far side of the rings just off the planet’s eastern limb. The ringed planet features several moons. The brightest, 8th-magnitude Titan, shows up through any scope. You’ll need a 4-inch or larger instrument to spy 10th-magnitude Tethys, Dione, Rhea, and Iapetus. Although the last of these varies from 10th to 12th magnitude as it orbits Saturn, it appears brightest well west of the planet in early July. Mars and Saturn certainly stand out in the summer evening sky. Unfortunately, the

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A ST R O N O M Y • JULY 2014

N

MORNING SKY Mercury (northeast) Venus (east) Uranus (southeast) Neptune (south)

same can’t be said for Pluto. The distant world glows at magnitude 14.1 — 1,000 times fainter than the naked-eye limit under a dark sky — among the background stars of northern Sagittarius. You’ll need an 8-inch or larger scope to detect its dim glow visually, though a camera can record it through a smaller instrument. The dwarf planet reaches opposition and best visibility July 4, when it rises at sunset and climbs highest in the south around 1 a.m. local daylight time. Although its magnitude doesn’t change all month, it reaches peak altitude — the best time to search

COMETSEARCH A fresh comet brushes the Lion’s mane If Comet PANSTARRS (C/2012 K1) lives up to expectations, observers who target it through a 4-inch or larger telescope should be in for a nice show. Astronomers predict this visitor from the distant Oort Cloud should reach 7th or 8th magnitude in July. But don’t wait too long. The comet is approaching the Sun in our sky and will disappear in evening twilight by mid-July. The window of observing opportunity is tighter still because the Moon’s glow spreads its light into the evening sky as the nights tick past. The best views should come during the month’s first week. By the time the sky darkens completely, about two hours after sunset, PANSTARRS sits about 10° high in the west-northwest. Before the sky grows fully dark, find the Sickle asterism

Dwarf planet Pluto at its best

that forms the head of Leo the Lion. Target Gamma (γ) Leonis, and pump up your scope’s power on this pretty binary star. The system’s two yellow stars follow a leisurely 510-year orbit and currently appear a comfortable 4" apart. Now that you have warmed up, you’re ready for the comet. First, identify 4th-magnitude Mu (μ) Leo and 3rd-magnitude Epsilon (ε) Leo, the two suns at the end of the Sickle’s curved blade. During early July, PANSTARRS tracks to the southsouthwest along a path that runs parallel to the imaginary line joining these stars. As the comet approaches closer to the Sun, our star heats the icy nucleus and causes it to shed gas and dust. The gas molecules become ionized (losing one or more electrons), and the

SAG IT TA R IUS

E

BB

July 1

29

6

11

16

21

26

31

Path of Pluto

0.05°

Although distant Pluto glows dimly at 14th magnitude, it’s fun to track down as it treks across the rich star fields of northern Sagittarius. ASTRONOMY: ROEN KELLY

for it — a half-hour earlier every week. To track down this object, first find 2nd-magnitude Nunki (Sigma [σ] Sagittarii), the star marking the northeastern corner of the handle in Sagittarius’ Teapot asterism. Next, locate 29 Sgr, a magnitude 5.2 star that lies 6° north and a bit west of Nunki.

Pluto remains within 0.5° (30') of this orange sun throughout July. A fainter star, the 7thmagnitude variable BB Sgr, resides 19' east of 29 Sgr and also proves useful in detecting Pluto. These two anchor the finder chart above. Pluto’s westward motion in July carries it 1.2' south of BB Sgr on the 8th and 2.5'

Comet PANSTARRS (C/2012 K1) N July 1

4 E Path of Comet PANSTARRS +

LEO

7 g

13

10

13 22

¡

Catch Comet PANSTARRS crossing northwestern Leo in early July before it disappears into the Sun’s glare. ASTRONOMY: ROEN KELLY

solar wind then blows these ions into a tail that points directly away from the Sun (toward the east). Pressure from sunlight pushes the ejected dust particles into a diffuse fan that curves gently away from our star.

A low-power view should reveal both tails. At higher power, the tails seem to sprout from a condensed inner region called the “coma.” If the comet produces lots of gas, you might detect the coma’s greenish hue.


Mercury glows before dawn Capella

TAURUS

AU R IG A

Aldebaran

Venus Mercury 10° Castor

G E MI N I

Betelgeuse

ORION

July 15, 30 minutes before sunrise Looking east-northeast Mid-July marks the peak of Mercury’s summer predawn appearance. Look below brilliant Venus to find the innermost planet. ASTRONOMY: ROEN KELLY

south of 29 Sgr on the 21st. Whenever you observe, sketch or image the stars around Pluto’s position and return to the same field a night or two later. The object that moved is Pluto. Although it appears as a mere point of light, imagine what this frigid world really looks like. We’ll find out next July when NASA’s New Horizons spacecraft flies past this enigmatic world. As midnight approaches, Neptune pokes above the eastern horizon. The magnitude 7.8 planet lies in central Aquarius and shows up fairly easily through binoculars. It climbs 40° high in the south by 4 a.m. local daylight time. To get to its position, draw an imaginary line between the 4th-magnitude stars Tau (τ) and Theta (θ) Aquarii. Neptune lies to the left of this line’s midpoint. As July begins, Neptune stands 1.9° northeast of 5thmagnitude Sigma Aquarii. This gap dwindles to 1.4° at month’s end. A telescope at high power reveals the ice giant’s 2.3"-diameter disk and blue-gray hue. Uranus lies one constellation east of Neptune, in Pisces the Fish, and trails about 90 minutes behind its sister world. The best views come as

twilight starts to break and Uranus appears roughly halfway from the southeastern horizon to the zenith. The planet travels slowly relative to the background stars, so its position changes little all month. Look for it some 2° south of 4th-magnitude Epsilon (ε) Piscium. Uranus shines at magnitude 5.8, which is bright enough to see with naked eyes under a dark sky. Binoculars easily bring it into view in the same field as Epsilon. Through a telescope at medium magnification, the planet shows a disk 3.5" across with a distinct blue-green color. As twilight first appears, Venus rises in the east. It shines brilliantly at magnitude –3.8, far brighter than any other point of light in the sky. The planet resides in Taurus the Bull in early July, passing 4° north of 1st-magnitude Aldebaran on the 2nd. It races eastward all month, crossing the northern tip of Orion on the 17th and 18th and traversing half of Gemini by the 31st. When viewed through a telescope, Venus’ disk appears 11" across and nearly full. Mercury makes a brief appearance in July’s predawn

LOCATINGASTEROIDS Close encounters of the asteroid kind percentage of the light that hits it than Ceres does, and because it orbits closer to the Sun than its sibling, Vesta also receives more light. Ceres shines at magnitude 8.4 in early July, some three times dimmer than magnitude 7.1 Vesta. To find the pair, start at 3rdmagnitude Zeta (ζ) Virginis. During early July, both asteroids lie within 1.5° of this star. The finder chart below shows stars to magnitude 8.8, so you should be able to tell which points of light are Ceres and Vesta. To confirm a sighting, plot a half-dozen stars visible in a low-power field of view centered near the objects’ positions. Return to this field a night or two later, and determine which pair of dots moved against the background stars.

Asteroids 1 Ceres and 4 Vesta appear closer to each other in early July than they have since astronomers discovered them in the 19th century’s first decade. On the evening of July 1, just 19' separate them. The gap closes to 10' — one-third the Full Moon’s diameter — on the 4th and 5th. Although they glow brightly enough to spot through binoculars, you’ll get a real thrill from seeing both in the same telescopic field. Ceres is the largest object in the main asteroid belt between the orbits of Mars and Jupiter. Its gravity molds it into a spherical shape, which is why astronomers also refer to it as a dwarf planet. Despite its size, Ceres typically is not the brightest object in the asteroid belt. Vesta’s surface reflects a greater

Ceres and Vesta have a historic meeting N VIRGO

c

July 1 July 1

6

90

6 11 11 E

16 Path of Vesta 21 26

26 31

16

21 Path of Ceres 80

31

74 1°

The two brightest asteroids pass within 10' of each other in north-central Virgo during July’s first week. ASTRONOMY: ROEN KELLY

twilight. It reaches greatest elongation July 12, when it lies 21° west of the Sun and stands 7° high in the east-northeast 45 minutes before sunrise. Coincidentally, that morning Mercury also lies 7° east (to the lower left) of the much brighter Venus, which serves

as a guide to the magnitude 0.4 innermost planet. Mercury maintains its altitude for the next few days and brightens slightly, so it becomes even easier to see. Point a telescope at the planet on the 15th, and you’ll see a nearly half-lit disk that spans 7.5".

GET DAILY UPDATES ON YOUR NIGHT SKY AT www.Astronomy.com/skythisweek. W W W.ASTR ONOM Y.CO M

43


ASKASTR0

Astronomy’s experts from around the globe answer your cosmic questions.

TARGET TIMES Q: HOW DO ASTRONOMERS KNOW HOW LONG TO MAKE AN EXPOSURE OF ANY GIVEN OBJECT? John King, Clackamas, Oregon A: To get a good estimate of the exposure times for a target, astronomers need to understand the telescope and instrument characteristics as well as the requirements of their own scientific measurements. How well an instrumenttelescope combination generally performs depends on the scope’s size, the detector’s sensitivity (which is just how many photons of light the system can detect per second when observing an object of a given brightness), and the sources of “noise” (which can obscure the data). Some of the noise sources are internal and may not depend on the exposure time, such as the readout noise on a CCD detector; this is a consequence of the system converting and reading electronic signals. Other sources of noise do depend on the exposure time, like the noise from the sky background. The measurement of the object itself also has noise, which is often called “shot noise.” (Generally, the amount of shot noise relates directly to the number of photons captured.) Astronomers — armed with this noise information, the brightness of their astronomical targets, and the goal of the science they are planning to do — calculate the required exposure time to achieve a specific signalto-noise ratio (S/N) on that target. For some types of science, like galaxy searches, the S/N can be low, maybe 3 to 5. (A S/N of 3 means the target’s signal is three times brighter than the noise.) For other types of science, like searching for exoplanets by how they tug on their parent

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A ST R O N O M Y • JULY 2014

stars, the S/N needs to be much higher, perhaps 100 or 1,000. In some situations, other criteria are at work. For example, rapidly changing objects might allow only for a short exposure time before the object changes. To get a high enough S/N, the astronomer might have to take many short exposures and combine the results. In other situations, the scientist must find a larger telescope or a more sensitive instrument to get the required data. Bob Goodrich W. M. Keck Observatory, Mauna Kea, Hawaii

Q: HOW CAN A QUARKANTIQUARK INTERACTION MAKE AN ELECTRON? A QUARK IS AN ELEMENTARY PARTICLE AND IS NOT MADE OF AN ELECTRON AND OTHER PARTICLES. Ted Varga Orem, Utah

A: You are absolutely correct that a quark and an antiquark are fundamental particles, yet

Our star’s surface is always changing, so NASA’s Solar Dynamics Observatory takes a short-exposure image of the Sun every 10 seconds. Astronomers take longer exposures of objects that don’t change as often. NASA/SDO

they can interact and form new ones. When they meet, they intermingle and form a “virtual photon” — a photon that lives for only a very short time. A photon is another name for a particle of light, like those that make up what you see from a light bulb or those that compose higher-energy X-rays. A virtual photon can violate some laws of physics, as long as its lifetime is less than a value

Quirky conversion

Electron Decay

Collision

Virtualn photo

Positron

Up quark

Up antiquark

The collision of an up quark and an up antiquark can create an electron and positron because the collision forms a virtual photon, which decays into an electron and its antiparticle, a positron. ASTRONOMY: ROEN KELLY

determined by the photon’s energy and a physical constant (called Planck’s constant). This “loophole” is related to something called Heisenberg’s uncertainty principle. A virtual photon briefly lives and then decays into new particles. Here is one simple example of a quark-antiquark interaction: 1. An up quark (electric charge +⅔) interacts with an up antiquark (charge –⅔). 2. They form a virtual photon, which has no charge but does have a mass. (A photon with mass is a violation of the laws of physics.) 3. The virtual photon decays within the time limit allowed by Heisenberg’s uncertainty principle, sometimes into an electron (charge –1) and an anti-electron, called a positron (charge +1). A quark and antiquark that annihilate each other can form other quark pairs and other elementary particle pairs such as a muon and an anti-muon. Nature


provides many other ways that quarks can combine. Howard Matis Lawrence Berkeley National Laboratory, Berkeley, California

Q: WERE THE UNIVERSE’S EARLY GALAXIES MUCH DIFFERENT FROM THE GALAXIES OF TODAY? Lindsay Van Bohmker Albuquerque, New Mexico

A: Yes! General comparisons of galaxies in the early universe (or similarly, the “high-redshift” universe) against those in the local universe (within about 20 million light-years of Earth) reveal that these two groups can be remarkably different. The reason why galaxies appear so different between our local universe and the distant one is because we are observing galaxies at different stages of their evolution as we look out in space. Telescopes are time machines, albeit ones that run only in reverse, and so the farther out we look with them, the progressively younger universe we see. Furthermore, we do not observe the universe from any special vantage point. So if we make the reasonable assumption that the physical laws we measure in the local cosmos are universal, we can conclude that the galaxies we observe in the early universe are analogous to the predecessors of the local galaxies. Thus, the differences we see between the different populations of galaxies provide direct insights into the nature of galaxy evolution. One way to distinguish galaxies is by their star formation rates, or the “vigorousness” with which they form new stars. When we look close to home — in our Milky Way, the neighboring Andromeda Galaxy (M31), and even the local “starburst” galaxies like the Cigar Galaxy (M82) — we observe these

galaxies forming stars at a meager rate of about 1 to 10 solar masses per year, on average. Galaxies in the early universe were far more active on average than our Milky Way. Astronomers have used space-based observatories, such as the Hubble, Spitzer, and Herschel telescopes, to conduct large surveys of distant galaxies, and they commonly observe star formation rates of hundreds of solar masses per year. As stars live, the nuclear fusion at their cores produces elements heavier than helium, which astronomers call metals, much to the dismay of our chemistry colleagues. When these suns die and spew those metals into space, winds and stellar explosions transport that material and “pollute” the galaxy. We would therefore expect that younger galaxies would have fewer metals in comparison to galaxies that have experienced multiple successive periods of star formation. Many studies have conformed this. For example, using Hubble’s near-infrared capabilities, astronomers have found the average abundances of metals have nearly tripled over the past 10 billion years. The shapes of galaxies in the early universe differ from those today in many ways as well. We group most massive galaxies (roughly the size of the Milky Way or larger) in the nearby universe into two general classes: “late-type” spirals (like our galaxy and M31) and “early-type” ellipticals (like M87). We also have a class for irregular galaxies (like the Magellanic Clouds). But even a glance at the Hubble Ultra Deep Field image — a 270-hour exposure of the highredshift universe — suggests a startling diversity in the shapes of galaxies in the early universe. Instead of spirals and ellipticals, most of these galaxy shapes need an entirely different vocabulary of “tadpoles,” “clumps,” and

Over the past 20 years, astronomers have found that galaxies in the early universe tend to be clumpy, instead of disk-shaped or elliptical. They often refer to these as “tadpole” galaxies. NASA/A. STRAUGHN, S. COHEN, AND R. WINDHORST ASU/THE HUDF TEAM STSCI

“chains” to describe them. And when we find high-redshift galaxies with shapes reminiscent of local spirals and ellipticals, these objects differ from galaxies near us. For example, elliptical galaxies at a redshift of 2 (when the universe was about 3.5 billion years old) of the same mass as those today are more compact — they have more mass within a smaller radius — by roughly a factor of three compared to their local counterparts. Michael Rutkowski University of Minnesota, Minneapolis

Q: HOW DO SCIENTISTS KNOW WHAT SPECTRAL LINES BELONG TO WHICH COMPOUND? Zbigniew Komala Chrzanow, Poland

A: Each atom and molecule has its own light fingerprint that, like yours, is unique. But unlike yours, this fingerprint is made of light. Elements and compounds emit identifying sets of “colors,” or wavelengths, of light. (“Colors” is in quotes because the light is not always visible, extending to infrared and radio bands on one side and ultraviolet and gamma rays on the other.) No two color combinations are the same, allowing astronomers to accuse specific chemicals of being in stars, gas clouds, or planetary atmospheres. But how did astronomers get these chemicals’ fingerprints in

the first place? Just like in a crime drama, they brought the atoms downtown (to the station). And by “station,” I mean laboratory. There, chemists put the atoms through all kinds of trials, where they vary the temperature, collect the light that results, and precisely determine the different wavelengths that make that light up. Once the fingerprints are “in the system,” astronomers can go look for matching sets in space. It may sound simple, but consider this: Few things in the universe are made of one pure substance. Astrochemists, as those who work in this field are called, have to separate the signature of hydrogen from the signature of helium from the signature of ethylmethylamine, which is like trying to determine what a person’s fingerprint looks like when 10 other suspects’ prints are on top of it. Sarah Scoles Associate Editor

Send us your questions Send your astronomy questions via email to askastro@astronomy.com, or write to Ask Astro, P. O. Box 1612, Waukesha, WI 53187. Be sure to tell us your full name and where you live. Unfortunately, we cannot answer all questions submitted.

W W W.ASTR ONOM Y.CO M

45


IMAGER PROFILE

GERALD RHEMANN imaging from near and far

With remote observatories in Namibia and the Alpen foothills, this Austrian imager can lock his lens on any comet or nebula he likes. text and images by Gerald Rhemann

My first encounter with astronomy wasn’t until 1986. Intrigued by the frequent media reports about the return of Halley’s Comet, I decided to have a look through a big telescope myself. I traveled to the western suburbs of Vienna — the capital city of Austria and my hometown — where the historic Kuffner Observatory and its 10.6-inch (270 millimeters) refracting telescope live. But what I saw through the eyepiece disappointed me. Even through this big refractor, Comet 1P/Halley appeared as nothing more than a foggy patch — no evidence of the impressive tails that shone through in photographs. Still, Halley aroused my interest enough that a couple of years later, in 1989, I purchased a telescope and mount. I wanted to make images that captured the same level of detail I had seen in photos of that comet, detail that the eye alone can’t see. Plus, because I was the owner of a photography shop, I had ready access to all the other stuff I needed — cameras, lenses, a darkroom, and experience.

For several months, the author (pictured above) had the opportunity to remotely control an astrograph located in Nerpio, Spain. With it, he captured IC 2177, the Seagull Nebula in Monoceros (right). This image had 21.9 total hours of exposure — the longest of any object the author has ever captured. (ASA 8-inch f/2.9 hyperbolic astrograph, FLI PL 16803 CCD camera, HαLRGB image with 180, 555, 224, 140, and 217 minutes of exposure, respectively)

Comets in the foothills My backyard, however, was not an ideal observing spot. Vienna’s light-polluted skies didn’t lead to photographic success. Fortunately, I met Michael Jäger, the most experienced and successful comet imager in Gerald Rhemann has been sky-shooting since 1989. His work has been featured in scientific papers and on NASA websites.

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A ST R O N O M Y • JULY 2014

Austria. Because Jäger and I share an interest in taking portraits of the solar system’s oldest inhabitants, a deep and lasting friendship developed between us. He showed me his favorite dark-sky sites: observationfriendly spots in the Austrian Voralpen. In these foothills of the Alps, less than an hour’s drive from my home, light pollution is nearly nonexistent.


The author captured Comet Lovejoy (C/2013 R1) on the morning of December 14 from Jauerling, a mountain in the Austrian Voralpen. The CCD’s sensor was sensitive to blue light and therefore accentuated the ion tail structures, whose carbon monoxide causes the hue. The comet was active and powerful enough that its ion tail visibly changed from one day to the next. The image is a two-panel mosaic. (8-inch f/2.9 ASA hyperbolic astrograph, FLI PL 16070 CCD camera, LRGB image with 5-minute exposures through each filter for each panel)

The region around Antares (Alpha [α] Scorpii) is one of the most amazing and beautiful in the entire sky, containing a complex mix of emission and reflection nebulae, dust lanes obscuring background stars, and star clusters. The author took this six-panel mosaic from Namibia over the course of three nights. (8-inch f/2.9 ASA hyperbolic astrograph, FLI PL 16070 CCD camera, LRGB image with exposures of 35, 25, 25, and 40 minutes, respectively, for each panel)

For imaging bright comets or comets at low altitude under the transparent Voralpen skies, I have portable equipment: an Astrosysteme Austria (ASA) DDM60 mount and an ASA 8-inch f/2.9 hyperbolic astrograph. Although trekking out there is a challenge and requires discipline, especially on a cold winter night, it feels worth the effort when I can capture crisp shots of comet tails streaming through space. But creating those pictures is no small task. Both the imaging and the processing of dynamic observations like these are timeconsuming. Because a comet perceptibly

moves in the field during the exposure — and sometimes its tail structure changes quite quickly as well — processing observations isn’t straightforward. To get both pinpoint star shots and a sharp comet image, I first remove the stars. Then, going back to the original picture, I remove the comet from the star field, and — finally — I put them back together again. That might sound easy, but it is not. My images are so precise that I report positional observations to the International Astronomical Union, which has designated my observatory in Eichgraben C14.

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A ST R O N O M Y • JULY 2014

The era of chemical film I first imaged deep-sky objects and comets through an 8-inch Celestron and later a 5.2inch Takahashi Epsilon 130 astrograph. After I became more proficient, I decided to purchase a Schmidt camera, then the most suitable instrument for comet imaging. The camera was a small one, only suitable for use with 35mm film, and it was tricky to work with: I had to cut the film and load the pieces into the film holder without scratching them or getting any dust or moisture on them — and I had to do this in an improvised darkroom in the


Observing hot spots Eichgraben, Austria

EUROPE Voralpen, Austria

ASTRONOMY: ROEN KELLY

A FR IC A

Tivoli, Namibia

This portrait of reflection nebula IC 4592 also shows IC 4601 in the lower left. (8-inch f/2.9 ASA hyperbolic astrograph, FLI PL 16803 CCD camera, LRGB image with exposures of 55, 30, 20, and 50 minutes, respectively)

back of my car. But the hardship provided valuable practice, and I worked myself up to a larger Schmidt camera that was suitable for 6x6cm plates. With a focal length of 450mm and a focal ratio of f/2.0, this camera was fast and produced great images across the entire field of view. In those days, commercial film just wasn’t ready for astroimaging. We photographers had to alter it a bit. Using nitrogen gas, we hypersensitized the film to reduce reciprocity failure, which makes the film less responsive after a certain amount of exposure time. We also had to develop and print the film ourselves, which required access to a darkroom. In view of all these difficulties, only a few amateurs worldwide attempted serious astrophotography. With the Schmidt camera, however, and doing considerable preparatory work, I obtained several hundred images of comets and deep-sky objects.

Step into the digital age In 2003, I recognized that the time of film had passed, and I switched to CCD astrophotography. Meanwhile I had acquired a 14-inch Cassegrain telescope with a prime focus option at f/3.0. On this instrument, I

installed my first CCD camera, a Starlight Xpress SXV-H9. Imaging with this camera opened a whole new world and new feeling for me. Because I could immediately see what I was photographing, I could be sure the image was in focus and the mount was tracking properly. Moreover, the digital “darkroom” rendered unimaginable possibilities in processing plausible, as the throughput increased enormously. There are always trade-offs, though: lots of cables and lots of electricity — both of which made traveling to observing sites difficult. Not one to be deterred, I solved the problem by building an observatory in the backyard of my weekend house in Eichgraben, Lower Austria. It has a roll-off roof and is fully remote-controlled — I can obtain images wherever I am. The observatory has a 12-inch ASA 12N astrograph at f/3.6 on an ASA DDM85 direct drive mount and a Finger Lakes Instrumentation ML8300 CCD camera.

Under southern skies Even though I now have many nearby observing options, the summer nights at

The author’s remote-controlled observatory in Eichgraben, Lower Austria, contains a 12-inch ASA 12N astrograph at f/3.6 on an ASA DDM85 mount. He also observes from the Austrian Voralpen and Namibia, where he has a remote setup. W W W.ASTR ONOM Y.CO M

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On an average night, the seeing in Eichgraben is only moderately good. But in spring, it sometimes is decent enough to use the ASA Barlow Corrector to get a longer focal length (2,070mm) with a 12-inch ASA 12N astrograph at f/6.8, as the author did to obtain this image of Bode’s Galaxy (M81). (FLI ML8300 CCD camera, LRGB image with exposures of 240, 110, 70, and 140 minutes, respectively)

In this April 1997 image, Comet HaleBopp’s (C/1995 O1) tail stretches up to the Double Cluster in Perseus (NGC 869/884). The observations were recorded on Kodak Pro Gold 6x6cm plates. (225/255/450mm Schmidt camera, exposure of 5 minutes)

Austrian latitudes are short and the weather is unstable. Southern objects are visible at low altitudes or not at all. To make up for what my region lacks, I travel to Namibia every two years. My next trip to southwestern Africa will be my seventh. At the Southern Sky Guest Farm Tivoli, the owners specialize in hosting astronomers. You can rent a telescope, a mount, and an observatory, or you can take your equipment with you and install it for the length of your stay. The owners adapt everything to the needs of skywatchers. Excellent meals 50

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are available — even in the middle of the night — and you can have a relaxed stay with like-minded people. The farm is on the edge of the Kalahari Desert, making the climate dry. From May to September, which is Namibian winter, the nights last 12 hours and stable high-pressure systems dominate the weather. Namibia, twice the size of California, has only 2.5 million residents, most of whom live in a few cities far from the farm. Because Namibia sits on the Tropic of Capricorn, the center of the Milky Way transits the zenith,

giving visitors like me full access to our galaxy’s core wonders. During my 2010 stay in Namibia, I installed the same type of equipment that I have in my observatory in Eichgraben in a friend’s nearby Southern Hemisphere observatory. By 2012, that observatory was fully remote-controlled, and I have access to this 12-inch astrograph whenever I want. In the future, I plan to use this telescope for comet searching. The probability of finding a new visitor to the inner solar system is much greater in the Southern Hemisphere than in the north, where several professional automatic comet-search programs are already in place. Maybe I will discover a new object as intriguing as the comet that first inspired me to put my eye to a telescope. In that quest, I will sometimes use the Southern Hemisphere telescope from my European home, but I won’t always stay put. Distance astrophotography is no substitute for actually being on location and enjoying transparent skies with my own senses while creating images that enhance what we can see on our own.


Operating a telescope in Namibia via remote control, the author obtained this image of NGC 2170 in Monoceros. (12-inch f/3.6 ASA astrograph, FLI ML8300 CCD camera, LRGB image with exposures of 230, 140, 140, and 170 minutes, respectively)

Comet Lemmon (C/2012 F6) was mostly visible in the Southern Hemisphere. The author captured it April 21, 2013, by remotely controlling his telescope near Guest Farm Tivoli in Namibia. (12-inch f/3.6 ASA 12N astrograph, FLI ML8300, LRGB image with exposures of 6 minutes through each ďŹ lter)

Although the transparency of Namibian skies is almost always perfect, the seeing is not. The night the author obtained this image of NGC 6726, however, the seeing happened to be great, so he used the longer focal length of the 12-inch ASA 12N astrograph at f/6.8. (FLI ML8300 CCD camera, LRGB image with exposures of 60, 50, 40, and 50 minutes, respectively)

TO SEE A GALLERY OF GERALD RHEMANN’S IMAGES, VISIT www.Astronomy.com/toc. W W W.ASTR ONOM Y.CO M

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TRICKS OF THE TRADE

Enhance your

observing with filters Not seeing enough detail on planets? Light pollution getting you down? In each case, the solution may be a small piece of glass. by Michael E. Bakich

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elescope, $6,000. Mount, $9,000. Eyepieces, $2,000. You’re ready to rock, right? Not so fast. Whether you paid this much for your setup or just a few hundred dollars, there’s a low-priced accessory that will — I guarantee — improve your view. It’s the oft-overlooked astronomical filter. Adding one, or a set, to your equipment is like adding a turbocharger to your new Corvette.

Michael E. Bakich is a senior editor of Astronomy who learned to value the view through filters decades ago.

Serious planetary observers consider a varied color filter set a necessity. These filters each screw into the barrel of a 1¼" eyepiece. ASTRONOMY: WILLIAM ZUBACK

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Sure, the car, like the scope, performed well before. But after? Woo-hoo, it’s smokin’!

What filters do If you’re unfamiliar with astronomical filters, I’m addressing this initial — important — point to you: No filter makes any part of any astronomical object brighter. Because filters subtract light of certain wavelengths, they all make targets fainter. So when you hear, “Wow! This filter makes the nebula so much brighter!” translate it as, “Wow! This filter makes the nebula so much easier to see!”

In my experience, beginning amateur astronomers take a while to warm up to filters. It may be because the view through most filters seems unappealing. We all want to appreciate the image from an aesthetic viewpoint as well as a scientific one. But knowing what filters will do can dramatically improve your observing.

Color filters The first type of filter I want to describe has important functions, but I guarantee you that making an object “pretty” isn’t one of them. A color filter is a carefully made


Celestron’s UHC/LPR Filter reduces the transmission of wavelengths produced by mercury vapor, highand low-pressure sodium lights, and natural sky glow. CELESTRON

The Oxygen-III (OIII) filter is a true narrowband filter. It transmits just the two lines from doubly ionized oxygen emission. An OIII filter works well on planetary nebulae. CELESTRON

piece of glass that passes (transmits) a wavelength range (color) through while blocking (absorbing) all others. Its purpose is to exaggerate differences in brightness. Observers using color filters see an image with only shades of gray, which confounds them. Nearly all criticisms of color filters I’ve heard indicate that the amateur astronomer was looking for changes in color rather than changes in brightness. I asked my pal Don Goldman, owner of Astrodon Filters, about this. “Even with no filter,” he says, “a visual observer cannot see color in most objects. They see grayscale images because the color receptors in our eyes are not sensitive enough for the small amount of light coming through to activate them, even when we use large telescopes.” Goldman also says that some observers claim they can see greenish hues through larger telescopes when they observe the

brightest objects. “That’s because our color vision is most sensitive in the green,” he states. “But color filters pass only a fraction of the visible light that we can detect compared to using no filter, so there is even less light to activate the sensors that weren’t activated with no filter.” Color filters reveal light from different levels in a planet’s atmosphere. And they may boost the performance of your optics … a little. While filters will not eliminate optical defects in a telescope, they will help improve image definition even through a low-quality system. Observers occasionally use color filters to suppress the effects of our atmosphere. This does work, although to a limited extent. Using a #25 Red filter on objects low on the horizon and orange and yellow filters for objects higher in the sky does improve the view. Here’s why. Scattering interposes a luminous veil between the observer and the target. Scientists have shown that for particles of a given size in a planet’s atmosphere, the scattering is inversely proportional to the fourth power of the wavelength of the light. Put more simply, violet light, which has a wavelength of 400 nanometers, scatters 16 times more than deep-red light, which has a wavelength of 800nm. Our clear daytime sky is blue as a result of this property. Unfortunately, although the science is sound, in practice I’ve found the benefit from using such a dark filter as a #25 is small when you view anything near the horizon.

The numbers game Manufacturers label color filters along their circumferences. To use one, just screw it

Several manufacturers offer filter sets. This one from Celestron contains a #15 Yellow, #21 Orange, #80A Blue, and an ND-25 neutral density filter. CELESTRON

into the eyepiece barrel. You can do that because eyepiece filters have threads that match the threaded inside barrels of eyepieces. Most filters fit 1¼" eyepieces, while the rest fit the 2" models. In some cases, you may prefer to hold the filter between your thumb and your pointing finger and move it back and forth between the eyepiece exit lens and your eye. This maneuver lets you make a quick comparison between the filtered view and the unfiltered one. Be aware that this technique has resulted in numerous dropped and broken filters, especially in cold weather when gloves are necessary. Certain manufacturers make filter holders. Such units allow you to pre-load up to five filters. You then slide the unit back and forth to select which filter to view through. Most of my friends who use such a device leave one filter slot empty so they also can observe objects unfiltered. Each filter also carries a number. Manufacturers refer to color filters by Wratten

HOW MUCH LIGHT GETS THROUGH? This list shows the most common color filters along with the percentage of light that they transmit.

This image shows how you can stack filters (because they screw into one another as well as into eyepieces) to allow less light through or to obtain a desired effect. ASTRONOMY: WILLIAM ZUBACK

Color filter Transmission (percent) #3 Light Yellow 88 #8 Yellow 83 #11 Yellow-Green 40 #12 Yellow (minus Blue) 74 #15 Deep Yellow 66 #16 Yellow-Orange 58 #21 Orange 46 #22 Deep Orange 36 #23A Light Red 25 #25 Red 14

Color filter Transmission (percent) #32 Magenta 13 #38A Dark Blue 17 #44 Light Blue-Green 16 #47 Violet 3 #56 Light Green 53 #58 Green 24 #80A Blue 28 #81A Light Orange 82 #82A Light Blue 73 #85 Amber 63

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same filter. (See the list of filters and their transmissions on p. 53.) So, which color filters are essential? My late observing buddy, Jeff Medkeff, once gave me his recommendations: “If I could keep only two of my filters, they would be #21 Orange and #82A Light Blue,” he said. “If I could keep a third, I would make it #25 Red. And if you pressed me, the fourth would be #80A Blue. These would be my recommendations for a first kit.”

Rather than continually screwing filters into eyepieces, many observers use a slider like Lumicon’s Multiple Filter Selector. This accessory allows you to load up to five filters. Note how this user has left the far right slot empty so he can compare filtered views to an unfiltered one. ERIC GRAFF

numbers. Kodak purchased the rights to this system and began manufacturing filters in 1912, and it has been the standard ever since. Filters for photography, astronomy, and other applications all use the same numbers. All filter numbers in this story are Wratten numbers. When Kodak implemented the system, lower numbers transmitted more light. Through the years, however, filter makers created new colors, so new ones no longer follow this relationship. One thing beginners should keep in mind is that color filters work better in conjunction with larger telescopes. It’s a simple rule of light throughput. For example, I’ve tried to use a violet filter on my 4-inch refractor to see cloud features on Venus. It just doesn’t work. The filter transmits a mere 3 percent of the light hitting it. When I switch to an 11-inch Schmidt-Cassegrain telescope, however, I can see those features easily through the

Specialty filter: neutral density Another type of filter common among observers is the neutral density filter. It reduces the light (by absorbing it) across all wavelengths equally. In other words, it filters all colors, just not preferentially. Neutral density filters for visual use come in a wide range of transmissions, from 80 percent all the way down to 1 percent. You can create even darker values, or non-standard ones, by stacking filters. In general, astronomers use light (high transmission) neutral density filters when observing the planets and dark (low transmission) ones when looking at the Moon because our lone natural satellite pours so much light into the field of view.

Specialty filter: polarizing Sometimes, observers want to see only light of a specific orientation. For this, they choose polarizing filters, which have the added benefit of reducing glare. The most common application is for sunglass lenses. In astronomy, double star observers often use them when one of the stars is much brighter than the other. The filter reduces the glare from the brighter (primary) star, making the companion easier to see. (To learn more about polarization, see p. 11.)

Some observers have used polarizing filters to make deep-sky observations during Full Moon, generally the worst possible time to view celestial objects. They report a significant contrast gain when they point their scope 60° from the Moon’s position and astounding results when they view between 80° and 90° from our natural satellite. I’ve tried this, and it seems to work better with low-power eyepieces. At higher magnifications, the polarizing filter helps a bit, but because the field of view is smaller than the one through a low-power eyepiece, not as much light is getting through, so the limiting magnitude (the faintest star you can see) appears to suffer. Several manufacturers make variable neutral density filters, which result when light passes through two polarizing filters, one of which rotates. Such a setup varies the light transmission from about 3 percent to 40 percent. As with neutral density filters, the most frequent use is for lunar observing.

Specialty filter: light pollution reduction Observers call all astronomical eyepiece filters beyond those listed above deep-sky filters, and this is a special breed indeed. They come in two varieties: broadband and narrowband. “Band” refers to the range of wavelengths the filter transmits. Some manufacturers call their broadband versions light pollution reduction (LPR) filters. Using these filters from the middle of a city, for example, will show some improvement in the images. Broadband filters are many and varied, but I have yet to convince myself that they are worth the money. They do filter out some unwanted light, but they tend to work better from a dark site or one with only mild light pollution.

These two sketches of the Trifid Nebula (M20) show the effect of using a deep-sky filter on reflection nebulae. Because a reflection nebula contains light of all wavelengths, a filter will dim it considerably. In this example, applying an Orion UltraBlock filter (right), one of several light pollution reduction filters, extinguished M20’s bluish northern lobe almost completely, except for a hint of haziness around its central star. The view of the part of M20 composed of emission nebulosity improved. JEREMY PEREZ

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Noted amateur astronomer Eric Graff sketched the Orion Nebula (M42). He used a 6-inch f/6 Newtonian reflector, a 30mm Plössl eyepiece, a 2x Barlow lens, and ultra high contrast (UHC) and Oxygen-III (OIII) filters. He created the unfiltered sketch (left) February 19, 2014, one through his UHC filter (center) on the 20th, and the OIII version on the 21st. He brilliantly captured the progressive darkening of the field of view, the loss of star brightness (and the general decrease in the number of stars), and changes to the appearance of the nebulosity. ERIC GRAFF

Specialty filter: Oxygen-III On this subject, my friend Bob Haler, owner of Lymax Astronomy, says, “From my personal experience, the only filter that seems to have miraculous anti-light pollution abilities is the Oxygen-III (OIII).” Haler points out that he has used OIII filters in ridiculously light-polluted environments (like a parking lot full of mercury vapor lamps) and gotten excellent views of the Ring Nebula (M57), the Dumbbell Nebula (M27), and other bright nebulae. “I am not saying that it is just like observing these objects from a dark location far from city lights,” Haler says. “What I am saying is that you can get some good views and might be able to show them off in less than ideal conditions.” Haler’s favorite narrowband filter gets its name because it lets only light from doubly ionized oxygen pass through. Yes, I said doubly. OI is the designation of neutral

oxygen. OII is singly ionized oxygen, so OIII stands for the doubly ionized version. (I note with pleasure that astronomy is not the only science with weird nomenclature.) Generally, the OIII filter has a bandwidth of around 10nm, centered over two spectral lines with wavelengths of 496nm and 501nm. Planetary nebulae and supernova remnants benefit from this filter because these objects emit strongly in OIII wavelengths. But don’t overlook emission nebulae, especially if the object is bright and the light pollution is high. Try an OIII filter with an 8-inch or larger telescope, and point it toward the Orion Nebula (M42). You can thank me later.

Specialty filter: Ultra high contrast The ultra high contrast (UHC) filter has a wider bandpass (as much as 26nm) than other narrowband filters but a much thinner one than any broadband filter. It boosts

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This graph shows the transmission of a typical light pollution reduction filter. In theory, the filter passes wavelengths emitted by celestial objects and blocks those from earthly sources. ASTRONOMY: ROEN KELLY

Specialty filter: Hydrogen-beta The Hydrogen-beta (Hβ) filter has the narrowest bandpass of all, no more than 8nm. Its transmission centers on the Hydrogenbeta line, which has a wavelength of 486.5nm. Amateur astronomers usually purchase this filter for one purpose: to observe the elusive Horsehead Nebula (Barnard 33) in Orion. And it works. By blocking all other wavelengths, this filter creates extreme contrast between the black sky background (and the dark nebula) and the meager amount of Hβ light the nebula behind B33 emits. Using an Hβ filter, I have observed the Horsehead through telescopes with apertures as small as 5 inches. A few other nebulae look good through this filter, including the California Nebula (NGC 1499) in Perseus and the Cocoon Nebula (IC 5146) in Cygnus, but the number is small, making the price per object a bit high.

Soup up your system

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the overall contrast by making the background sky appear slightly darker. Because it absorbs a bit more light on the red end of the spectrum, it gives the stars a slight blue color. Objects that benefit from the UHC filter are bright and diffuse nebulae.

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This graph shows the transmission of a typical Oxygen-III (OIII) filter. The two peaks occur at 496 and 501 nanometers. OIII filters work best on planetary nebulae. ASTRONOMY: ROEN KELLY

There’s no getting around it. Whether you observe the Moon, planets, or deep-sky objects, filters will improve your views. Every advanced amateur astronomer I know has several (to lots) in his or her observing kit. Viewing through astronomical filters will take a little getting used to, but after a few sessions, you’ll wonder how you ever got along without them. W W W.ASTR ONOM Y.CO M

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NORDIC NIGHTS

Hunting aurorae in the Arctic

The aurora’s dance serves as a backdrop to the Imagine Peace Tower of light — a memorial to John Lennon from Yoko Ono, his widow — near Reykjavík, Iceland. CARL BERNHARDT

One editor’s Icelandic adventure featured awesome vistas, rich Nordic culture, and stunning displays of the northern lights. by Liz Kruesi

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hen you see the aurora shimmer and dance overhead, you understand why people chase them. In 2013, Astronomy Production Editor Karri Ferron and I each experienced the joy of the glimmering northern lights on separate trips to the Arctic with the magazine’s travel partner, MWT Associates, Inc. For me, it was during a weeklong tour to Iceland in March (see p. 58 for Ferron’s trip to Norway). While there, I learned about the country’s impressive geology and rich culture — but the draw, of course, was the spectacular northern lights.

Green and purple aurorae shimmer above rental cabins near Iceland’s southern coast. CARL BERNHARDT

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Water, as liquid and ice As soon as we landed at the airport just outside the capital city of Reykjavík, we jumped on the tour bus that brought us to the Blue Lagoon, a geothermal spa within the lava fields of Iceland’s Reykjanes Peninsula. The warm waters are rich in minerals (with silica and sulfur) and extremely relaxing. Managing to stay awake, we continued on to see some of the sights in Reykjavík, including the hilltop Perlan building. The observation deck gave wonderful views of the city and the Esja mountain range in the background. While there, I quickly realized why the recommended packing list included windproof pants and coats — the wind was incredibly strong and made the 30° Fahrenheit (–1° Celsius) air feel much colder. We spent the following four days on the southern coast of the island country. First we explored the “Golden Circle,” composed of Þingvellir National Park, the Haukadalur geothermal area, and the huge waterfall Gullfoss. Þingvellir served as a crucial meeting location for nearly nine centuries, and it has been a UNESCO World Heritage Site for 10 years. Haukadalur hosts hot springs and natural geysers, and its main attraction is the geyser

Strokkur that erupts every few minutes and spews water some 50 feet (15 meters) high. The group witnessed a few eruptions — including two just seconds apart. The third site in this golden trifecta is Gullfoss, a tiered waterfall with transparent light-blue water that tumbles down some 105 feet (30m). Although most of that water was frozen in March, Gullfoss was still an incredible scene. On our first night away from city lights, the aurora greeted us. Pale clouds spread across the sky, brightened to a green color — caused by emission from oxygen atoms in Earth’s atmosphere — and then danced in S shapes. That band faded while another arc formed and spread; then another appeared concentric with that one. After this early-evening show, many of us headed to bed while others stayed up to witness purple and green aurorae. Iceland is a country of ice and fire, and we certainly witnessed that theme throughout our trip. The next day, the group drove to a nearby lava field to view the solidified rock from the 1783–4 volcanic eruption of the Lakagígar fissure in the southern part of Iceland. (The gases released during the volcanic blows caused famine across the island, Liz Kruesi is an Astronomy associate editor.


Comet PANSTARRS (C/2011 L4) was visible against the aurora’s green curtain on our last night in Iceland — March 24, 2013. CARL BERNHARDT

The author explores the mossy dried lava from the Lakagígar fissure eruption. JACOB HOBERG Icelandic horses tend to be short and stocky; they also have beautiful thick winter coats. JACOB HOBERG

which led to the deaths of about a quarter of the country’s population.) The eruption spewed some 3.4 cubic miles (14 cubic kilometers) of roiling lava, pushing clumps out onto the land, which then dried in lumpy shapes. Now, hundreds of years later, moss covers this vast field of bumpy lava. While still in the southern portion of the country, we explored a number of glaciers and Vatnajökull National Park. Pictures and words cannot convey how beautiful these places are. We first visited Jökulsárlón Glacier Lagoon, where seals swam among chunks of clear blue ice and in front of mammoth ice mounds. Gray pebbles lined the beach and added contrast to the blue colors. We then traveled to two other “outlet” glaciers of the huge ice cap Vatnajökull, which is the largest such feature in Europe and one of the biggest glaciers in the world. We got to experience the full natural beauty of the country. It rained while we visited, and that moisture turned the moss, which grows over many places on the island, a deep green. That vegetation lay in the foreground of the light teal-blue of the

water and ice, while the deep gray and crisp white of the snow-covered basaltic mountains stood as a backdrop.

The sky’s glimmering lights On our last day in southern Iceland, we visited a folk museum in Skógar, which included an open-air portion. The stillstanding one-room houses felt claustrophobic — I wasn’t keen on spending five minutes in them, let alone living in one. But I’m sure the close quarters kept the inhabitants warm in the winter months. We toured the small (some 400 square feet [37 square meters]) Lutheran church on the property, and the man who founded the museum — now in his early 90s — played a bit of organ for us. Later that evening, as we made our way along the southwest of the island and back to the capital city, those of us seated on the right side of the bus spotted a pale green cloud. I watched it brighten in spots; there was no mistaking what it was — a fast-paced auroral show had just begun. (At least half our group

Gullfoss, a 105-foot-tall (30 meters) waterfall, is one of three sites along Iceland’s “Golden Circle.” LIZ KRUESI Light-blue water and ice highlight the Jökulsárlón Glacier Lagoon’s gorgeous vistas. LIZ KRUESI

was so excited that we were screaming like preteens at a One Direction concert.) Our bus driver chased a break in the clouds to a park on the northwest side of Reykjavík, which gave us a clear view across the bay. For about 40 minutes, the lights danced across the sky, brightening, swirling, fading, and repeating the cycle. The aurora’s dominant color was green, but we also spied red, purple, and blue at times. Unfortunately, my amateur photography skills couldn’t capture these variations. But even if my photographs were perfect, they could not convey how incredible it is to watch the northern lights shimmer in the sky. The next night, our last evening in Iceland, we didn’t expect to top that aurora viewing, but we still hoped to see something in the sky. We traveled about 30 minutes outside Reykjavík, where we set up our cameras under the moonlit landscape. A few travelers photographed Comet PANSTARRS (C/2011 L4) while others found their way around the constellations in the sky. At about 10:30 p.m., even with a Full Moon, the northern lights appeared. This time they lasted just 10 minutes, but they glowed green as they danced across the sky as a goodbye. Out of our three clear nights in Iceland, we batted a thousand for witnessing the aurora. These light shows in the sky, in addition to the incredible sights on land, made for a fantastic trip. Iceland is a beautiful country filled with impressive geologic wonders and striking colors — on the ground below, the field in front, and the sky above. W W W.ASTR ONOM Y.CO M

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Another editor endured high winds and rough seas to watch the northern lights dance in the land of eternal night.

The 445-foot (136 meters) MS Midnatsol carries cargo as well as aurora chasers. KARRI FERRON A globe sculpture erected on the island Vikingen in the Norwegian Sea marks the latitude of the Arctic Circle. KARRI FERRON

by Karri Ferron

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o see the northern lights dance from a truly dark sky has been a dream of mine since I first saw a faint green glimmer of them from my suburban Milwaukee home as a child. So when I received the invitation to chase the aurora borealis along the Norwegian coast this past November with Astronomy magazine’s travel partner, MWT Associates, Inc., I jumped at the opportunity. And the journey was more than I ever could have imagined, featuring unpredictable Arctic weather, rich Nordic culture, and some wonderful displays of northern lights from the deck of the MS Midnatsol.

Land of eternal night After five flights in 48 hours, our group of 17 astronomy enthusiasts arrived in Kirkenes, in the far

The author and her mom, Barb Ferron, explored 12 ports along the Norwegian coast during their trip. KARRI FERRON

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northeastern part of Norway, to start a northern lights adventure. But even before we began the hunt, we had our first awesome Arctic experience: sunset by 2 p.m. local time. True, we knew such an early dusk was coming, but exploring a town devastated by World War II in midafternoon pure darkness was eerie to say the least. The following morning, the MS Midnatsol arrived in port to take us on our southbound journey along the Norwegian coast. The 445-foot (136 meters) vessel is a combination cargo/cruise ship, so it makes many stops of different durations in ports along its route. But it’s perfect for aurora viewing, as the back half of the top observing deck has no lights, which enhances the spectacle. Many aboard the ship received their first peek at the aurora our first afternoon on the ship. I, unfortunately, missed this initial glimpse, as I had foolishly gone inside to warm up (temperatures never went above freezing, even during the day), but my travel companions graciously shared pictures and descriptions of the experience. I thought my luck had changed later that first night when the captain announced during the middle of dessert an aurora sighting. I wasn’t going to miss one again, so I ran up four flights of stairs and burst on deck (no coat) — only to discover it was a false alarm. But there were small breaks in the clouds, so I hurried to my room, bundled up, and headed back into the Arctic air. For the next few hours, we saw two small spurts

of auroral activity, but after dancing for a few seconds, each fizzled. After that, clouds dominated the remainder of the evening, and the crowd gradually dispersed.

Top of the world The following morning, we arrived in Hammerfest, billed as the northernmost city in the world. Many of us took a bus tour of the city to get the most out of the short time we were in port. Stops included the UNESCO World Heritage Site dedicated to the northernmost point of the Struve Geodetic Arc (a chain of survey triangulations stretching across 10 countries that yielded the first accurate measurement of a meridian) and a city overlook that showed all the rebuilding necessary after German troops burned the area to the ground during World War II. That night saw a combination of music and northern lights. After some sporadic auroral activity, the MS Midnatsol made her way into Tromsø, the “capital” of Arctic Norway. A large group of us headed to the Arctic Cathedral for a midnight concert by a trio of talented local musicians. We heard a variety of classical music interspersed with some traditional Norwegian folk tunes. The setting and songs produced a magical experience and sent us to bed with a theme song for the northern lights to dance to in our dreams. The following morning, we had the opportunity for an extended excursion on land while the MS Midnatsol continued Karri Ferron is Astronomy’s production editor.


Snow-capped peaks and deep blue waters surround Norway’s northwestern coastal towns. KARRI FERRON

south. She dropped us off in Harstad, a town on the northeastern part of the large island of Hinnøya, and we ventured out on buses. We began at the historic Trondenes Church just north of the town, where we attended a service and watched our ship leaving port. After time at the museum next door, which is a premier cultural heritage site for the late Middle Ages, we rode the bus all along the island, seeing amazing views of the mountains, fjords, and agricultural areas before rejoining the MS Midnatsol in Sortland.

Gusty viewing After a day filled with such fascinating Nordic culture, everyone was in a great mood for aurora hunting that night. During dinner, however, the MS Midnatsol started rocking. The next thing we knew, the cruise director was asking people to be extremely careful on the ship, as we were experiencing gale-force winds (Beaufort scale of 8). And she wasn’t kidding;

A faint auroral curtain and the stars of the Big Dipper provide a stunning display off the back of the MS Midnatsol. SUSAN MCNEVIN

it was nearly impossible to walk without bumping into walls and dancing with various poles throughout the ship. Many were queasy, some enjoyed the roller coaster, and very few souls were willing to venture outside to enjoy the crystalclear skies. Things calmed as the MS Midnatsol finally arrived at port in Bodø at 2 a.m., and some then ventured outside. They received a treat at 4 a.m. with a 30-minute show of periods of green dancing lights. As I was one of the queasy ones during the storm, I missed the spectacle. Although upset during breakfast as I heard the tales of stunning aurorae, I had to stay positive. There were still two nights of viewing left. Before that, though, we had an exciting day ahead of us: We were officially leaving the Arctic, as we crossed south of latitude 66°33'. A globe on the island Vikingen marked this moment for us, and the ship’s crew offered a ceremonious spoonful of cod-liver oil to the passengers, washed down with wine. Admittedly, the cod-liver oil was quite awful, but it was worth the souvenir spoon we received for participating. That night produced the true souvenir for those hunting the northern lights, though. Almost as soon as we were away from the port of Rørvik, the light show began despite some lingering clouds. We witnessed some faint arcs and a few striking striation peaks. Some 10 minutes later, the clouds came, the wind picked up, and a hail/snow mix pounded us. And then just as fast as the small squall came, we had clear skies again and more subtle arcs.

Travelers on the ship’s observing deck witness a spectacular show of dancing lights. ROBERT STEPHAN

After one more squall with winds that refused to calm, we experienced a breathtaking curtain of light for about 30 minutes. Pictures weren’t perfect because of the ship’s motion, but the show made up for any uneasy stomachs. This was the first time the observing deck was truly filled with passengers, so everyone finally saw the phenomenon that is the northern lights and went to bed happy.

A trip to remember On our final full day aboard the MS Midnatsol, we stopped in Trondheim (historically called Nidaros, the capital of Norway during the Viking Age). It’s home to the Nidaros Cathedral, a Gothic work of art with Romanesque roots that’s an important Christian pilgrimage destination to this day. And despite the capital city being Oslo, it’s the location where kings held their coronations (and today hold their consecrations). It was spectacular to see both inside and out. Clouds and rain unfortunately greeted us on our final night and continued as we disembarked in Bergen. Yet despite the crazy weather, we headed home with memories of the Arctic and its fascinating lights dancing in our heads.

FIND MORE PHOTOS FROM THE EDITORS’ ARCTIC ADVENTURES AT www.Astronomy.com/toc. W W W.ASTR ONOM Y.CO M

59


BINOCULAR STARGAZING

12

sweet summer bino treats

Grab your binoculars and explore double stars, asterisms, and star clusters. by Phil Harrington

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sn’t it ironic that while summer nights are the shortest of the year, more showpiece objects are visible this season than any other? That means we have our work cut out for us, so let’s get started with these 12 targets. We begin with four globular clusters (and an asterism sprinkled in) that you’ll find in the constellation Ophiuchus the Serpent-bearer. First up is M14, nestled in an empty area of eastern Ophiuchus. Aim about halfway between Sabik (Eta [η] Ophiuchi) and Cebalrai (Beta [β] Ophiuchi) at the upper left (northeast) shoulder of the figure. Drop about one field of view southward to a faint parallelogram of stars.

Globular cluster M14 shines at magnitude 7.6 and measures 11.7' across. It lies in a lonely area of sky far from any bright star. MARTIN C. GERMANO

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M14 lies a little to the north of the halfway point, near a close-set pair of 7th- and 9thmagnitude field stars. Like the telescope Charles Messier used to discover M14 in 1764, binoculars reveal only a nebulous smudge. But you will see it. You’ll find our next globular, M9, just east of the halfway point between Sabik and Xi [ξ] Ophiuchi. Aim there, and you’ll see a right triangle of dim stars. M9 lies along the triangle’s hypotenuse. Coming in at 8th magnitude, this globular cluster is small but reasonably easy to spot as a tiny celestial cotton ball. Moving southward, place Antares (Alpha [α] Scorpii) at the western edge of your binocular field, and look to the opposite side for a close-set pair of stars of magnitudes 5.7 and 5.9. The globular cluster M19 sits just 1° to the duo’s southeast. Like M9 and M14, M19 looks non-stellar through most binoculars. Reader Jim

Elliott from Lee County, North Carolina, also points out that an unusual arc of three optical double stars curves around M19 to the northeast. I call this curious assembly of stars, which includes 26 and 28 Ophiuchi plus SAO 185033 (and the three fainter stars that accompany each of them), the Dish O’ Doubles because it reminds me of a satellite dish with M19 at the focus. Take a look at it, and see how it strikes you. On paper, M62 sounds like a twin of M19. But when you look for it, about half a binocular field to the south, it proves to be more difficult to find. Viewing from the Naylor Observatory outside Harrisburg, Pennsylvania, reader Dave Mitsky describes M62 as “a small, featureless fuzz through my 8x42 binoculars. However, my 15x70 binoculars reveal a brighter stellar core.” One of my favorite summertime asterisms lies in Scorpius just 1.5° southwest of

Open star cluster Stephenson 1, also known as the Delta Lyrae Cluster, shines at magnitude 3.8. Its namesake, Delta (δ) Lyrae, is the gorgeous blue and gold double star dominating the image. The yellowish star shines at magnitude 4.5, and the blue one glows at magnitude 5.6. BERNHARD HUBL


NGC 6819 shines in Cygnus at an impressive magnitude 7.3. It’s small, though — only 5' in diameter. BERNHARD HUBL

M62. If you’re a gardener, you’ll recognize it right away as a Garden Trowel. Give John Davis from Amherst, Massachusetts, kudos for this one. Davis draws the Trowel from three 7th-magnitude stars set in a south-pointing triangle and a trail of three 6th- and 7th-magnitude stars meandering off to the north. While most of the Trowel’s stars are white, a couple of them shine with a subtle golden glint. Let’s now head northward toward Lyra. Even the smallest pocket binoculars will resolve Delta (δ) Lyrae in the constellation’s northeastern corner as two neighboring stars. The brighter of the pair, Delta2, looks orangish, while fainter Delta1 is bluishwhite. The two Delta stars also belong to a scattered open cluster nicknamed the Delta Lyrae Cluster and cataloged as Stephenson 1. Through 70 millimeter binoculars, you may spot a concentration of eight to 10 faint cluster stars just west of Delta Lyrae. Moving eastward into Cygnus, center on Sadr (Gamma [γ] Cygni) at the center of the Swan’s body. We visited here two summers ago to find M29 to this star’s southeast. While it’s also worth a second glance now, this year let’s focus on NGC 6819 about 8° west of Sadr. It shines at 7th magnitude and spans just 5'. You can miss this little open cluster easily if you casually scan the area. Phil Harrington is a contributing editor of Astronomy and author of Cosmic Challenge (Cambridge University Press, 2010).

But a careful search will reveal its gentle glow centered in a triangle of field stars. A second faint open cluster, NGC 6910, is just a Full Moon’s diameter north of Sadr. English astronomer William Herschel discovered NGC 6910 in 1786 and described it as “pretty bright, pretty small, poor, pretty compressed, stars from the 10th to 12th magnitude.” Of course, that was through his 18.7-inch reflector. Binoculars reveal a small, subtle glow with one or two faint stars just poking out. Head back to Sadr, but only briefly, before continuing southeastward toward Epsilon (ε) Cygni. Focus on a spot about three-quarters of the way there. Can you see a clumping of faint stars spanning an area a little larger than the Full Moon? That’s open cluster Ruprecht 173. You’ll count two dozen stars through most binoculars, with the four brightest forming a narrow diamond-shaped asterism. The diamond’s easternmost star is the well-known Cepheid variable X Cygni. Every 16 days, X peaks at 6th magnitude. At minimum, it dips to 7th magnitude. Our final stop is the colorful triple star Omicron1 (ο1) Cygni, which you’ll find 5° west-northwest of Deneb (Alpha Cygni). Fourth-magnitude Omicron1 glows pale orange, while its 5th-magnitude companion, 30 Cygni, appears bluish. Defocusing your binoculars slightly will enhance the colors, but refocus to spot a third member, a 7th-magnitude sun

Open cluster NGC 6910 is a tough catch through small binoculars, but most observers can spot it from a dark site. MARTIN C. GERMANO

southeast of Omicron1. You’ll need a steady hand to spy it through 10x binoculars. None of these stars is a true double but just lineof-sight coincidences in a rich star field. These 12 targets only hint at what the sky has in store for your binoculars this summer. Use them at your favorite observing site, and you quickly will realize that for stargazing, two eyes are better than one.

EXPLORE 13 MORE SUMMER BINOCULAR TARGETS AT www.Astronomy.com/toc. W W W.ASTR ONOM Y.CO M

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EQUIPMENT REVIEW

Astronomy tests

Celestron’s StarSense

Adding Celestron’s StarSense AutoAlign accessory to one of the company’s older telescopes lets you align its go-to drive much more easily than before. CELESTRON

This accessory allows you to transform your old go-to mount into one that aligns itself. by Phil Harrington ne of the tasks stargazers find most time-consuming is aiming a telescope toward an intended target. Go-to technology revolutionized amateur astronomy when it first appeared more than two decades ago. But most go-to mounts still required the user to initialize the system by aiming at several alignment stars. In an effort to make setup easier, many next-generation go-to mounts now do most of this initialization automatically. This equipment requires minimal action on the user’s part other than setting up the mount, flicking a switch, and sometimes entering time, date, and location. But what about those of us who already own older go-to mounts? To enjoy these state-of-the-art features, do we have to buy new ones? Not necessarily. That’s the beauty of the new StarSense AutoAlign add-on from Celestron. By mounting the AutoAlign unit on your telescope in place of the finder scope and then plugging it into your older Celestron mount’s auxiliary inputs, StarSense technology will automatically align the mount in a matter of minutes.

How it works

Phil Harrington is an Astronomy contributing editor and author of Cosmic Challenge: The Ultimate Observing List for Amateurs (Cambridge University Press, 2010).

Attaching the StarSense to your instrument is a simple task. Remove the existing finder scope, install the appropriate mounting bracket, and slide on the imager.

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StarSense uses a small built-in digital camera to take a series of sky images 6.88° wide by 5.16° high. The software then scans for bright, recognizable stars. That information, coupled with the data you input, allows StarSense to use a technique astronomers call “plate solving” to find the coordinates of the center of the captured image. That determines where the telescope is pointing. From that starting point, the observer can select from more than 40,000 celestial objects programmed into the hand controller’s database. Included with the AutoAlign unit is a matching StarSense hand controller (which takes the place of Celestron’s original NexStar hand controller), two mounting brackets, and an input cable to couple the imager to your mount’s auxiliary input. Please note that the mount must have two auxiliary inputs: one for the imager cable and one for the hand controller. Mounts with only one port for the hand controller, like the vintage CG-5 Computerized Mount I used for this review, require Celestron’s AUX Port Splitter ($19.95).

The company includes two mounting brackets. The smaller bracket is compatible with the Vixen-style dovetail bases found on Celestron’s refractors and reflectors, while the larger one matches the base you’ll find on Celestron’s Schmidt-Cassegrain and EdgeHD instruments. For this test,

How it performs The author attached the StarSense to his Celestron C6 telescope. This instrument rides on an older CG-5 mount, which required Celestron’s AUX Port Splitter. PHIL HARRINGTON


I mounted the larger bracket on my C6 Schmidt-Cassegrain telescope. With the StarSense in place, all I had to do was plug one end of the included auxiliary cable into the imager and the other end into the mount’s auxiliary port. After I attached the hand controller into the other auxiliary input, I was ready to go. One nice touch Celestron added was to make the StarSense hand controller the same shape as its NexStar controllers. That means you can stow it in the same holster as you had been using in the past. After turning on the unit, I entered the date and time and then selected the closest location in the hand controller’s database. The nearest choice was 11 miles (18 kilometers) away, which proved close enough for the StarSense’s purpose. The unit prompted me to press the “Align” button, followed by “StarSense Auto Align.” The telescope then began to move to different areas of the sky automatically. Each time the telescope paused, the hand controller’s display read “Acquiring Position,” followed by “Acquiring Image,” and finally “Sensing.” The telescope slewed to four positions in the process, two on each side of the meridian (the imaginary line that runs north to south passing through the overhead point). The instructions warn that if the unit doesn’t sense enough stars, the controller will read out “Too Few Stars” and move the scope to a different region of sky. While

PRODUCT INFORMATION Celestron’s StarSense AutoAlign Communication ports: RS-232 communication port on hand control; AUX interface and USB on camera Computer hand controller: Four-line, 16character backlit Liquid Crystal Display with 19 fiber optic backlit LED buttons Database: 40,000+ objects Weight: 17 ounces (482 grams) Price: $329.95 Contact: Celestron 2835 Columbia Street Torrance, CA 90503 [t] 310.328.9560 [w] www.celestron.com

strong twilight, terrestrial obstructions, heavy light pollution, and moonlight could be problematic, the StarSense had no problem completing the process from my moonless suburban backyard, which isn’t exactly a dark site. The naked-eye limiting magnitude there is about 4.5. The StarSense also offers a manual mode that lets the user select the area of sky for the alignment images. This is useful in locations with an obstructed horizon. Celestron warns, however, that this method is not as accurate as automatic alignment. Still, I found that it does offer reasonably good accuracy within that region of sky.

The StarSense hand controller’s database contains 40,000 objects. Celestron gave it the same shape as its other controllers. PHIL HARRINGTON

The first time I used the StarSense, I had to perform a second operation to align its center with that of my telescope — in effect the electronic equivalent of aligning a finder scope with the main instrument. This process required that I select a named star from its database and instruct the StarSense to go there. I chose Aldebaran (Alpha [α] Tauri). With a wide-field eyepiece in place, the scope slewed to Aldebaran’s general vicinity. It was a bit more than one field of view off. Using the hand controller’s arrows, I centered the star in the eyepiece, pressing “Enter” and “Align” when instructed. Once I finished this, the message “Realignment Required” appeared. This meant I needed to shut off the telescope, turn it back on, and repeat the AutoAlign process. Once done, the hand controller’s readout posted “Alignment Complete,” and I was ready to observe. And guess what? It worked perfectly. Purposely trying to throw it off, I chose widely separated objects, going from the Orion Nebula (M42) to Ursa Major’s Cigar Galaxy (M82), to the Ghost of Jupiter (NGC 3242) in Hydra, and then onward to Jupiter itself in Gemini. Each time, my target was in the eyepiece’s field of view.

How it rates

The StarSense AutoAlign accessory replaces the finder scope on older Celestron telescopes. The unit comes with two mounting brackets; pick the one that works with your instrument. PHIL HARRINGTON

I came away impressed with Celestron’s StarSense accessory. Despite the age of my CG-5 mount, the new unit worked perfectly the first time, and every time. Rather than manually initialize the go-to control when I went out, I simply set up the scope, hit “Auto Align,” and while the scope was doing its thing, I was inside making a cup of tea. What could be better than that? W W W.ASTR ONOM Y.CO M

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OBSERVINGBASICS BY G L E N N C H A P L E

Laser pointer debate

This handy observing tool faces regulation because of misuse.

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very now and then, one of my columns elicits enough reader response to merit a follow-up. Such is the case with a piece I wrote on green laser pointers (November 2013), in which I outlined their value to the amateur astronomer and the risks inherent in their misuse. An accompanying photo showing a green laser flash in an airplane cockpit prompted a comment from Fred Hoffman of Fort Bliss, Texas. “As an instrument pilot,” he wrote, “I’ve been lucky not to have been ‘lit up’ as in your photo. That happening on short final approach in very bad weather could be deadly.” Referring to an incident where a high school teacher became visually impaired after a student shined a laser pointer into her eyes, Peter Sacks of Pearland, Texas, commented: “I would like to see the sale of laser pointers legally restricted to those 18 years of age or older. This limitation is similar to the ban on the purchase of spray paint cans to people under the age of 18 as a way to limit the spray cans being used by juveniles for graffiti.” Such legislation is already on the books in Arkansas. Act 382 (HB1343) bans the sale of a handheld laser pointer to anyone under 18 while Act 1408 (HB2192) prohibits a minor from possessing a hand-held laser pointer without the supervision of a parent, guardian, or teacher. Other states and communities are considering similar laws. They won’t affect laser pointer abuse by criminals and miscreants 18 years or older, but it’s a step in the right direction. Other readers pointed out a related issue. For example, Laura

Graham of Powhatan, Virginia, leader of the International DarkSky Association’s Virginia chapter, wrote: “I understand that to use laser pointers to blind people is a very serious business. I do find it troubling, though, that the police are aware of this problem and do absolutely nothing to prevent other kinds of light pollution. They request that we light up our yards to fight crime — the more light, the better.” In all fairness to our men and women in blue, let’s acknowledge that they, like the general public, likely are unaware of the negative effects of lighting overkill. We need to get out the word that a motion-detector or low-wattage well-shielded light is more effective and energy-efficient than something with the light output of a searchlight beam. Some readers asked about lasers and astroimaging. Mike Howard of Simi Valley, California, inquired, “Does a green laser pointer show up in star pictures?” It depends on the strength and duration of the beam. To be on the safe side, imagers who cringe at the mere sight of an errant firefly may want to work from an area that’s free from any form of stray light — laser pointers included. Those who wish to use these tools for astronomical purposes also had questions. “Could you recommend a laser pointer — company and type — for a price under $100?” asked Jerry Green of Pinehurst, North Carolina. I always hesitate to suggest a preference to any particular brand of astronomical equipment for two reasons. First, I don’t want to rankle a quality company whose product I simply overlooked or

A green laser pointer can be a great observing tool as long as we use it responsibly. XOFC/WIKIMEDIA COMMONS

was unfamiliar with. Second, what works for me may not work for someone else. A number of reputable companies offer green laser pointers at prices well under $100. A hint: Look for one that’s advertised to work in cold weather, as ordinary green laser pointers tend to shut down as temperatures approach the freezing level. Several online sources sell green laser pointers at ridiculously low prices. There is a caveat, though, as Brian Vanderkolk of Buena Park, California, noted: “The Food and Drug Administration regulates all lasers in the United States, and pointers must emit less than 5 milliwatts (5mW), a level considered generally safe and unlikely to cause any permanent damage for safety reasons. Unfortunately, there are several shady companies selling pointer-like hand-held

FROM OUR INBOX ISON outrage Comet ISON (C/2012 S1) wasn’t the comet of the century; it didn’t deserve all the hype, much less its own special issue! In your article “Comet ISON’s final hurrah” (March, p. 50), Richard Talcott states that the comet reached 4th magnitude, making it visible to the naked eye only “under the darkest skies” and in urban areas “through binoculars.” If this was truly a once-in-a-century comet, anyone should be able to see it. It may have provided a “memorable show,” as you put it, but its audience had 6-inch telescopes and CCD cameras. — Mac Fife, Indianapolis No one was more disappointed in Comet ISON’s premature death than the editors of Astronomy. As we stated many times, scientists face a notoriously difficult task when trying to predict the brightness of a comet. With ISON, reality failed to live up to expectations. Its magnitude –2 peak just before it broke apart in late November was two to three magnitudes fainter than most predictions. And, unfortunately, we had to send our February issue to the printer just days before ISON’s demise. — Richard Talcott, Senior Editor

BROWSE THE “OBSERVING BASICS” ARCHIVE AT www.Astronomy.com/Chaple.

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lasers that exceed this power, some quite excessively.” Last year, a study by the National Institute of Standards and Technology revealed that most green laser pointers tested exceeded the acceptable 5mW cap. Just to be safe, let’s treat all laser pointers as though they were more powerful than 5mW and avoid aiming them in the direction of people, vehicles, or aircraft. Vanderkolk added: “It concerns me that the recent abuse of lasers as ‘toys’ may affect the ability of hobbyists such as myself to legally enjoy using these wonderful devices.” Like it or not, the dark side of green laser pointers has reared its ugly head. Spurred on by citizen and law enforcement complaints, government officials are looking into laws to limit, even ban, their use. It’s up to each of us to demonstrate the proper use of green laser pointers at public star parties, report to the appropriate authorities any incidents of laser pointer misuse, and make our state and local legislators aware of the value of these devices when used responsibly. Questions, comments, or suggestions? Email me at gchaple@ hotmail.com. Next month: a “Rodney Dangerfield” globular cluster. Clear skies!


MOBILE UPDATES What’s new at Astronomy.com. BY KARRI FERRON

Cosmic Adventures

OBSERVING TOOLS

The weird and wonderful of our universe Astronomy education isn’t just about textbooks and lectures. Show your children, students, or any other beginner a fun and engaging view of the cosmos with the video series Liz and Sarah’s Cosmic Adventures. In each episode, Astronomy magazine’s associate editors, Liz Kruesi and Sarah Scoles, take viewers on a tour of our beloved science and hobby with jokes, weird anecdotes, demonstrations, and a few outtakes. In their first year together, the duo tackled all aspects of astronomy, both serious and fun, from the dark universe and gravitational waves to big changes in astronomy and the impact of animal astronauts (and cosmonauts). Check out www.Astronomy.com/ cosmicadventures to join Liz and Sarah on their journeys, and contact them at cosmicadventures@astronomy.com to suggest ideas for future adventures.

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Summer observing videos Get outside on these warm nights to check out all this season’s sky has to offer. Find out where to start your exploration with Astronomy.com’s seasonal observing videos. In one, Senior Editor Michael E. Bakich explores the big events of the summer, including a stunning conjunction of Venus and Jupiter. In another, he focuses on warm-weather objects you can see through a small telescope, such as the Trifid Nebula (M20). Finally, Editor David J. Eicher shares 10 of his favorite summer deep-sky objects, including the Fireworks Galaxy (NGC 6946). Check out them all at www.Astronomy.com/seasons.

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Alfa Planetarium Monterrey, Nuevo LeĂłn, Mexico

The Observatory of the Alfa Planetarium is northeast of Mexico’s largest public observatory. The Observatory has two main telescopes: refracting telescope PGEJBNFUFSPQFOJOHBOESFGSBDUJOH UFMFTDPQFPGJOEJBNFUFSUP observe larger or nearby objects.

1IPOF   t   'BY   t NBJM!PCTFSWBEPNFDPN $PNNFSDF1BSL%SJWF+BDLTPO .4

Photograph by: Enrique Perez Garcia

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65


COSMICIMAGING

FROM OUR INBOX

BY A DA M B LO C K

What does it mean to be smart?

Use processing operators Last column, I discussed the “Lighten” and “Darken” blending modes in Photoshop, which you can use as an effect on an underlying layer. However, there are more powerful methods of combining blending modes. One is to enhance images according to an object-oriented approach. This month, I want to show you how to first use the “High Pass” filter on an image and then use “Darken” as an operator (something that has an effect on something else) blending mode for even finer control. The standard technique for using the “High Pass” filter on a luminance layer is to make two copies of it (left image below). On the upper layer, apply the “High Pass” filter by selecting “Filter,” then “Other,” and finally “High Pass” so that you see features of the scale you wish to capture — and ultimately enhance — through blending.

The author created an original luminance layer with two copies above it. He applied the “High Pass” filter to the upper layer and blended with “Overlay.” He didn’t use the bottom image. ALL IMAGES: ADAM BLOCK

Adjust the “Radius” slider to vary the scale-size of details in the object. For galaxies, these features could be spiral arms (large radius), dust lanes (medium radius), or ionized hydrogen (HII) regions (small radius). When you are satisfied, apply the filter and examine the gray image that results (middle image). This image functions as an operator image when used with the “Overlay” blending mode on the lower copy of the luminance image. “Overlay” will enhance structures in the “High Pass” filter layer that are brighter than the mid-gray value, making them brighter. Likewise, with “Overlay” active, those features that show up as darker than the midgray value will become even darker. The “High Pass” filter layer is a map of what features at a given scale are being made brighter or darker with “Overlay.” This contrast adjustment is striking and not often used at 100 percent strength. Instead, adjust the opacity of the “High Pass” (operator) layer to vary the effect.

In his article “Searching for smart life around small stars” (p. 28) in the February issue, Seth Shostak treats sentience and intelligence as if they were the same thing: “Suppose one in 10 of these [red dwarf stars] develops intelligent beings after 5 billion years, and that sentience remains present thereafter for one in 10 of those.” My dog is sentient, but I don’t expect her species to develop technology or advanced communication any time soon. I understand sentience to be consciousness that is capable of feeling and rudimentary thought, but intelligence also encompasses creativity, self-awareness, intentionality, judgment, and presumably some kind of long-distance communicative technology. I enjoyed this informative article and look forward to future articles from SETI scientists about one of the greatest searches humanity can be involved with. — Robert Walty, Stephens City, Virginia

As an example, I recently used a “High Pass” filter with “Overlay” on an image of the Pinwheel Galaxy (M33). After I applied the filter, the nearly resolved stars and HII regions became brighter while the dust lanes darkened. However, the small, bright structures within M33 needed no enhancements. Trying to bring out more detail in them made the image look overprocessed. On the plus side, the additional contrast made the dust lanes much more attractive. The puzzle becomes finding a way to enhance only the dust lanes without affecting anything else. Here’s how I did that. First, I created a “High Pass” layer with a medium-to-large scale and applied the “Overlay” blending mode as described above. Then I merged the “High Pass” layer

This “High Pass” filter result is a map of structures for a given radius. The author blended that layer with the copy of the image’s original luminance layer. Objects above the mid-gray value became brighter, and those below that threshold got fainter.

This screen shot shows the final result for the author’s image of the Pinwheel Galaxy (M33) in Triangulum. To create it, he blended the new enhanced layer he produced with the original layer using the “Darken” blending mode in Photoshop.

BROWSE THE “COSMIC IMAGING” ARCHIVE AND FIND VIDEO TUTORIALS AT www.Astronomy.com/Block.

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with the copy of the original M33 layer to create my enhanced image. Finally, I blended the two remaining layers using the “Darken” blending mode (right image). Although the final image shows enhancements in both bright and dark regions of M33, by blending with “Darken,” I brought out only the dust lanes (as I wanted) without having the brightening effect of the “Overlay” mode visible. This is a powerful way to globally control an image by using “Lighten” or “Darken” as an operator to separate combined effects into only those that are beneficial. I think you’ll find that by using this technique, you’ll be able to fine-tune the details in your data and make the final result more realistic.


Attention, manufacturers: To submit a product for this page, email mbakich@astronomy.com.

Image-processing tutorial

Color imager Celestron, Torrance, California Celestron’s NexImage Solar System Imager is a one-shot color imager that replaces the 1¼" eyepiece on your telescope and connects to your PC via USB 2.0. The 1280x720 CMOS sensor provides high-resolution images of the Moon and planets. The package includes iCap capture software and RegiStax stacking software.

IP4AP.com, Sanborn, New York Warren Keller and Rogelio Bernal Andreo again join forces to bring imagers the PixInsight Part-2 video tutorial series. Easy to follow fiveminute chapters cover nonlinear stretches, noise reduction, detail development, and other enhancements with PixInsight’s powerful multiscale wavelet transforms.

Price: $65 (streamed); $75 (DVD) [t] 716.864.7400 [w] www.ip4ap.com

Ritchey-Chrétien scope Astro-Tech, Norman, Oklahoma

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2.4-inch scope

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ASTROSKETCHING BY E R I K A R I X

The author made this sketch of SN 2014J and M82 on January 25, 2014. She observed with a 16-inch f/4.5 reflector using an 8mm eyepiece, which gave a magnification of 225x. She sketched on white printer paper with a super-fine black felttipped artist pen, a #2 graphite pencil, a 0.5mm mechanical pencil, charcoal, and a blending stump. ERIKA RIX

Star death In this column, I want to encourage you to sketch the last moments of a massive star’s life — an event known as a supernova — and the debris visible after such an explosion — a supernova remnant. Astronomers document hundreds of supernovae each year, but few shine brightly enough for visual observers to enjoy. On January 21, Steve Fossey, a faculty member at University College London, and his astronomy class discovered SN 2014J, a supernova that reached magnitude 10.5. Immediately, skywatchers pointed even the smallest telescopes at its host, the Cigar Galaxy (M82) in Ursa Major, to soak in the view. A supernova looks like a new star, which may glow for weeks before fading. SN 2014J was a type Ia supernova, one that occurs in a binary star system when a white dwarf accumulates material from its neighbor. Once the dwarf gathers as little

as 0.9 solar mass, it becomes unstable and undergoes a thermonuclear explosion. The former sun shines briefly with the light of 1 billion normal stars. The nearly uniform luminosity of type Ia supernovae makes them useful distance indicators and led to the discovery of the universe’s accelerating expansion. All other types of supernovae are the core-collapse variety, which happen when a massive star exhausts its nuclear fuel. The core implodes and — depending on its mass — either a central neutron star or a black hole remains. When you sketch such an event, indicate the supernova with a pointer for easy identification. Also, note its magnitude by comparing it to the brightness of nearby stars. Then record it by sketching it at the same size and darkness (for a black on white sketch) as

an equally bright star. During additional sessions, you will record its change in magnitude, so try to be as accurate as possible in your drawings. The second target for this month’s column is a supernova remnant called the Veil Nebula. Such an object marks the aftermath of an exploding star. The Veil Nebula is 1,400 light-years away in the constellation Cygnus the Swan. The entire complex spans nearly 3° and lies an equivalent distance south of Epsilon (ε) Cygni. Prominent segments include the Eastern Veil (NGC 6960), Pickering’s

Ferenc Lovró created this open-field eyepiece sketch of the Veil Nebula while observing through an Oxygen-III filter with a 12-inch f/5 reflector at 71x. He used heavy, smooth-surfaced art paper, a B pencil for the stars, and a 5B pencil for the nebulosity. The mosaic took two hours to complete and covers a 1.5° by 4.5° field of view. FERENC LOVRÓ

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A ST R O N O M Y • JULY 2014

Triangle (NGC 6979), and the Western Veil (NGC 6992/5). The remnant is a bit tough to see, but an Oxygen-III or Ultra High Contrast filter in a 10-inch or larger telescope will reveal it. You may see the entire loop through a low-power, wide-field eyepiece, but you’ll need to pan the area at higher magnifications to dig out the details. That means sketching multiple fields of view to capture the remnant. Start by drawing a circle that represents each field. The circles overlap, and the collective finished sketch shows each field boundary. Alternatively, you can eliminate the constraints of sketch circles and opt for a clean, open-field drawing. In the second case, sketch the field of view for an area containing a bright section of the Veil. Then nudge your telescope until roughly half the field disappears. The effect will be one where each field of view overlaps the previous one. When you overlap, it enables you to cross-reference star fields while you’re sketching your way through the loop. And here’s a little-known tip: Your dark adaption will have increased during the observation, so to complete the sketch, make a final pass to include missed nebulosity and faint stars. Questions or suggestions? Please contact me at erikarix1@ gmail.com.


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READER GALLERY

1 1. THE HUNTER’S SWORD Normally, the Orion Nebula (M42) is one of the most recognizable deep-sky treats. When imaged through narrowband filters, though, it has the same overall features as it does visually, but the dusty regions surrounding it tend to stand out more. (4-inch Takahashi FSQ106 refractor at f/5, SBIG STL-11000 CCD camera, Hα/OIII/SII image with 120-, 500-, and 900-second images totaling 12 hours of exposures) • Robert Fields 2. THE SOUTHERN SEAGULL This varied complex of nebulosity lies in the constellation Dorado. On the left side of this image is the bluish Southern Seagull Nebula (NGC 2032). The large rose-shaped cloud to its left is NGC 2035. At the bottom right, the round blue nebula is NGC 2020. To its right, open cluster NGC 2014 shines through the reddish nebulosity that surrounds it. (20-inch PlaneWave corrected DallKirkham telescope, FLI PL-09000 CCD camera, HαRGB image with exposures of 30, 3, 3, and 3 minutes, respectively) • Fred Herrmann

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3. OBSCURE OBJECT Ishida Weinberger 2 is a large ellipsoidal planetary nebula in Cepheus. It lies 850 light-years away and formed when a Sun-like star blew off its outer layers some 40,000 years ago. (16-inch RC Optical Systems Ritchey-Chrétien telescope at f/8.9, Apogee U16M CCD camera, Hα/ NII/RGB image with exposures of 390, 330, 75, 75, and 75 minutes, respectively) • Don Goldman 4. GALACTIC TANGO The Cocoon Galaxy (NGC 4490) zips through space with a smaller companion, irregular galaxy NGC 4485. The pair lies in the constellation Canes Venatici some 25 million light-years away. (14.5inch RC Optical Systems RitcheyChrétien telescope at f/9, Apogee U16M CCD camera, LRGB image with exposures of 560, 240, 220, and 240 minutes, respectively, taken remotely from the Rancho Hidalgo Astronomy and Equestrian Village near Animas, New Mexico) • Mark Hanson

3

5. PRETTY IN PINK Van den Bergh 93 is a complex of emission and reflection nebulae in Canis Major. This object is a northwestern extension to the much larger Seagull Nebula (IC 2177); vdB 93 forms the bird’s head. (14-inch Officina Stellare RC-360AST Ritchey-Chrétien telescope at f/8, Apogee Alta U16M CCD camera, LRGB image with exposures of 90, 75, 75, and 90 minutes, respectively) • Bob Fera

4

5

6

6. NEBULA IN NARROWBAND Emission nebula NGC 1491 in the constellation Perseus lies approximately 10,700 light-years away. Also known as Sharpless 2–206 and LBN 704, this is a star-forming region lit by radiation from newly birthed suns. (17-inch PlaneWave corrected Dall-Kirkham telescope, Apogee U16 CCD camera, Hα/OIII/SII image with exposures of 7, 4, and 5 hours, respectively) • Bill Snyder 7. BARELY VISIBLE DUST LBN 406 is an ultra-faint molecular cloud in Draco. Stellar winds from stars within it have sculpted it into fascinating shapes. Amateur astronomers often call it the Laughing Skull Nebula. (4-inch Takahashi FSQ-106 refractor at f/5, SBIG STF-8300 CCD camera, LRGB image with exposures of 600, 150, 180, and 210 minutes, respectively) • Bob Franke

Send your images to: Astronomy Reader Gallery, P. O. Box 1612, Waukesha, WI 53187. Please include the date and location of the image and complete photo data: telescope, camera, filters, and exposures. Submit images by email to readergallery@astronomy.com.

7

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To the ends of the cosmos

NASA/ESA/D. JEWITT UCLA

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An asteroid disintegrates

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A ST R O N O M Y • JULY 2014

Never before October 2013 had astronomers witnessed an asteroid breaking into pieces before their very eyes. The minor planet P/2013 R3, however, appeared on plates made with the Catalina Sky Survey and the Pan-STARRS telescope in Hawaii, broke apart over the course of several days,

and was imaged with the Hubble Space Telescope. “This is a rock,” said scientist David Jewitt of the University of California, Los Angeles, a planetary scientist who led the investigation of the surprising event. “Seeing it fall apart before our eyes is pretty amazing.”

P/2013 R3 was a main-belt asteroid lying some 298 million miles (480 million kilometers) from the Sun, so how it broke apart is a mystery. Space is too cold to have warmed ices within the rock, but perhaps centrifugal forces increasing its rotation rate caused its demise.


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SOUTHERN SKY

MARTIN GEORGE describes the solar system’s changing landscape as it appears in Earth’s southern sky.

September 2014: Mercury at its best I always love observing on September evenings. Not only is the coldest weather of the year a thing of the past, but the Milky Way provides a wide array of spectacular sights. And this September adds great planet watching to the mix. Mercury begins the festivities with a grand evening appearance that lasts all month. The innermost planet reaches greatest elongation September 21, when it lies 26° east of the Sun. This is Mercury’s best evening show of the year because the ecliptic (the apparent path of the Sun across our sky that the planets follow closely) makes a steep angle to the western horizon after sunset. In early September, you can find Mercury 6° high in the west and 25° directly below Spica, Virgo’s brightest star, an hour after sunset. The planet shines at magnitude –0.2, some three times brighter than Spica. The two objects make a beeline toward each other, however, and by the 21st, they are nearly on top of one another. Mercury passes just 0.6° south of Spica that evening, when they stand 13° high an hour after sunset. That same night, the planet appears 7" across and 58 percent lit when viewed through a telescope. By month’s end, Mercury spans 8" and shows a 41-percent-lit phase. After admiring Mercury and Spica, shift your gaze higher in the west to spot Mars and Saturn. On September 1, just 5° separate these two and a pretty waxing crescent Moon lies a similar distance away. Binoculars show this attractive trio the

best, but the naked-eye view isn’t too shabby. Mars passed Saturn in late August and now appears above its neighbor. As the two continue their eastward motions along the ecliptic, Mars travels faster because it orbits closer to the Sun. The Red Planet has its sights set on Antares, the heart of Scorpius the Scorpion, and on September 27 it reaches its target. This star has a distinctive ruddy hue, courtesy of its relatively cool surface temperature. Even its name suggests the star’s color, coming from the Greek words anti Ares, which mean “rival of Mars.” Mars and Antares lie 3° apart on the 27th. You can tell which is which because Mars lies to the right and shines a bit brighter (at magnitude 0.8). Through a telescope, Mars appears 6" across and shows little detail. Compared with the Red Planet, Saturn moves at a glacial pace. It remains among the background stars of Libra the Balance all month. Glowing at magnitude 0.6, the ringed planet shines two full magnitudes brighter than any of Libra’s stars. Saturn is almost always a superb telescopic object, and this month is no exception. The world’s disk measures 16" across at midmonth while the rings span 26" and tilt 22° to our line of sight. Even a small telescope shows the rings beautifully, particularly when Saturn lies high in the west in early evening. It is unquestionably the best object to show someone who has never looked at the night sky through a telescope

before. Spend at least a few minutes soaking in the glorious view. And, while you’re at it, keep an eye out for its 8thmagnitude moon, Titan. Mercury, Mars, and Saturn all set before midnight local time. The sky then stays planetfree until Jupiter rises shortly before the beginning of twilight. The solar system’s largest planet hangs low in the east about an hour before sunrise. It gains altitude slowly this month because the ecliptic makes a shallow angle to the eastern horizon before dawn at this time of year. Still, it shines so brightly (at magnitude –1.9) that it’s easy to pick out of the twilight sky. If you want to view Jupiter through a telescope, wait until it climbs higher in late September. On the 30th, the gas giant spans 34" and should show at least two dark belts sandwiching a brighter equatorial zone. It’s four bright moons — Io, Europa, Ganymede, and Callisto — also show up easily through any scope. The ecliptic’s angle also kills Venus. The inner planet rises only 30 minutes before the Sun on September 1 and won’t show up against the bright twilight unless you have perfect conditions. It will return to view in the evening sky in December.

The starry sky Many people confuse constellation patterns with asterisms. The former essentially use all of a constellation’s brighter stars to form a familiar shape — Scorpius the Scorpion and Orion the Hunter are two classic

examples. Asterisms, on the other hand, are recognizable patterns that either are smaller than a constellation or span two or more constellations. One attractive asterism is the Teapot, which is a group of stars entirely within Sagittarius the Archer. Although well known to Northern Hemisphere observers, it’s hard to recognize from south of the equator because it appears upside down. But September is a good month to try. First, lie on your back on the ground with your legs pointing south. Then, arch your neck back so you can see the prominent tail and stinger of Scorpius. Sagittarius will appear to the stinger’s left. The Teapot comprises eight of Sagittarius’ brightest stars, all located in the constellation’s northwestern part near Scorpius. It covers an area of roughly 10° in declination by 15° (one hour) in right ascension. Phi (ϕ), Zeta (ζ), Epsilon (ε), and Delta (δ) Sagittarii form the Teapot’s main body while Lambda (λ) Sgr marks the knob on the lid. Sigma (σ) and Tau (τ) Sgr represent the Teapot’s handle and Gamma (γ) Sgr locates the tip of the spout. Once you become familiar with the Teapot, it’s easy to find on future nights. Although the Teapot is the most prominent part of Sagittarius, the constellation and Archer’s shape extend much farther. Surprisingly, Sagittarius is nearly 75 percent bigger than neighboring Scorpius. Most of the rest of the Archer holds comparatively faint stars located to the Teapot’s east and south.


STAR DOME

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Planets are shown at midmonth

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THE ALLSKY MAP SHOWS HOW THE SKY LOOKS AT: 10 P.M. September 1 9 P.M. September 15 8 P.M. September 30

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Diffuse nebula Planetary nebula

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HOW TO USE THIS MAP: This map portrays the sky as seen near 30° south latitude. Located inside the border are the four directions: north, south, east, and west. To find stars, hold the map overhead and orient it so a direction label matches the direction you’re facing. The stars above the map’s horizon now match what’s in the sky.

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SEPTEMBER 2014 Calendar of events 1 The Moon passes 4° north of Mars, 0h UT Asteroid Harmonia is at opposition, 19h UT 2 First Quarter Moon occurs at 11h11m UT

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5 Venus passes 0.8° north of Regulus, 12h UT R FO

8 The Moon is at perigee (358,389 kilometers from Earth), 3h31m UT

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The Moon passes 5° north of Neptune, 12h UT

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Asteroid Victoria is at opposition, 12h UT

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Mira

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9 Full Moon occurs at 1h38m UT 11 The Moon passes 1.1° north of Uranus, 2h UT

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16 Last Quarter Moon occurs at 2h05m UT 20 The Moon passes 5° south of Jupiter, 11h UT

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The Moon is at apogee (405,845 kilometers from Earth), 14h22m UT

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STAR COLORS: Stars’ true colors depend on surface temperature. Hot stars glow blue; slightly cooler ones, white; intermediate stars (like the Sun), yellow; followed by orange and, ultimately, red. Fainter stars can’t excite our eyes’ color receptors, and so appear white without optical aid. Illustrations by Astronomy: Roen Kelly

FOR DEFINITIONS OF TERMS, LOG ONTO www.Astronomy.com/glossary.

21 Mercury passes 0.6° south of Spica, 2h UT Mercury is at greatest eastern elongation (26°), 22h UT 22 Pluto is stationary, 13h UT 23 September equinox occurs at 2h29m UT 24 New Moon occurs at 6h14m UT 26 The Moon passes 4° north of Mercury, 10h UT 27 Mars passes 3° north of Antares, 21h UT 28 The Moon passes 0.1° south of asteroid Ceres, 1h UT The Moon passes 0.7° north of Saturn, 4h UT The Moon passes 0.5° north of asteroid Vesta, 15h UT 29 The Moon passes 6° north of Mars, 17h UT


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Astronomy july 2014