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HERBERT S . ZIM, Ph . D . , Sc. D . and ROBERT H . BAKER, Ph . D . , D . S c .

Illustrated by JAMES GO RDON I RVING



Western Publishing Compa ny, I n c . Racine, Wisco nsin


A series of boo k s on nature s hould i n clude o n e o n t h e stars a n d p lan.ets . All ot her as pects o f nature-birds, flowers, rocks, and trees-are deta ils i n the g reat system that en compasses the heave n s . Noth i n g else i n nature c a n a rouse the feeli n g s of won d e r that are provoked by a n eclipse, a meteor shower, or even a close loo k at o u r nea rest n e i g h bor, t h e m o o n . The a rtist, J am e s Gordon I rving, worked w i t h skill a n d i m a g ination . H i s wife, Grace C rowe Irv i n g , assisted in re­ searc h . David H. Heeschen of the Ha rva rd Observato ry a n d I va n K i n g of the Un iversity of Illinois Observatory ' �helped with data a n d tables. Paul lehr, of the National � n d Atm ospheric A d m i n istration , checked text involvi n g m eteorology. Hugh Rice of the Hayd en Pla ne­ ta rium gave helpfu l advice, a n d our seasonal con stella­ tion c h a rts owe much to his p rojectio n s . Do rothy B e n n ett, fo r m a n y yea rs a member of the Hayden Pla n eta ri u m ' s staff, contrib uted g reatly t o our ed itorial p l a n n i n g . I s a a c Asimov, J o e a n d S i m o n e Gos ner a re t o b e cred ited for the latest revisio n s . Acknowle d g m ent is d u e the lowell, Hale (Mt. Wilson and Mt. Palomar), lick, a nd Yerkes observatories and to NASA for the use of photog ra p h s . R. H. B. H . S .Z. © Copyright 1975, 1956, 1951 b y Western Publishing Company, Inc. All rights reserved, including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by any electronic or mechanical device, printed or written or oral, or recording for sound or visual reproduction or for use in any knowledge retrieval system or device, unless permission in writing is obtained from the copyright proprietor. Produced in the U.S.A. by Western Publishing Company, Inc. Published by Golden Press, New York, N.Y. Library of Congress Catalog Cord Number, 75-314330

CONTENTS This is a book for the novice, the a m a teur, or a ny­ o n e who wants to e n joy the wonders of the heavens. It is a field guide, with information to help you un d ersta n d m o r e fully what you see . U s e this book w h e n you a re watc h i n g the sta rs, con stellations, and pla n ets. Thum b throug h it at odd m o m e nts to beco m e fa m ilia r with sig hts you may see; ca rry it alon g o n trips or vacations. ........................................




OBSERVING THE SKY.. Act i v i t i e s for the A m a t e u r.

The U n iverse a nd the Sola r Syste m..

......................... 12 16

The S u n a n d S u nlight

..................................... 28

Telesco p e s .

................................... 31



Cla s s ification . Star Ty p es .......


. ..... . .. ... . ......... .... .... . 38 42

Galax i e s...


CONSTELLATIONS No rth C i rc u m pola r Constellatio n s............... ..................


C o n stellat i o n s of S p r i n g . ......... ..... ...... .... .. . . ... ....... . .... . .... ....


Co n stella t i o n s of S u m m e r .... ... ... ....... . ... ... ... . ...... ... ...... . ........


Co n stella t i o n s of A u tu m n . ...

....................................... 80

C o n s tellat i o n s of W i nter


S o u th C i r c u m pola r C o n s tella tions .. ..... ... . . .. .... .... .. . . .. .... ....


THE SOLAR SYSTEM ........................ ................ ............................102 The Pla nets ..... . ..... . .


...............1 04

loca t i n g the V i s ible Pla nets..... .. . ...... .. .. . . .. .. ..... ... ... . ........ . ..124 Co m ets...................... Meteors



Haw to Observ e Meteors........ The Moa n............


.. .... ....... ... ......

.................132 ............................136

Ecl i pses ...... . .. .... ..... . ..... ... .... ...... .......... .. .. .......... . .. ...... .. . 150 APPENDIX (ti nted pa ges) . .. ...... . .... ... .. ... ... ..... .. ..... ......... ..... . .. .156 l i s t of Co n stellatio n s .... .. ..... ....... . ... ....... . .... ... . .... ... ... .......... 156 Objects for Observati o n . . ..... . . ... . .......................... INDEX



......................... ........... :.............................159


OBSERVI NG THE SKY Egyptian Pyramids

Sta rs a n d pla n ets have attracted ma n ' s attention since earl iest times. Ancient ta b lets and ca rvi n g s show that movements of p l a n ets were understood b efore 3000 B . C . l e g e n d says two C hinese astronomers who fa iled t o pre­ d ict an ecl ipse correctly i n 2 1 36 B.C. were put to death. The Egyptians placed their pyramids with reference to the sta rs . The circles of sto n e a t Ston e h e n g e may have been used to keep tra c k of lun a r eclipses. Astron omy is indeed the old est science, yet its importa n ce i n c reases a s scientists turn to the sta rs to study problems of physics which they can not ta c k l e d i rectly i n the l a b o ratory. As fa r back as h istory records, there were p rofessional a stronomers-long before there were p rofessional zoolo­ g ists a n d bota n ists . The Egyptians, C h inese, a n d Euro­ peans had court a stronomers. Their work often i nvolved t rying to p red ict future events, but their system, thoug h considered unscientific today, i nvolved observation a n d record i n g o f facts about stars a n d p l a n ets . These ea rly astro n omers, as well a s those of today, made rema rk­ a b le d iscoveries that changed ma n ' s outloo k on the world a n d himself. There has a lways been, too, an a rmy of a mateurs studying and enjoying the sta rs . Some make p ractical use of their knowledge-sailors, p i l ots, surveyors, but most study the heavens out of sheer i n te rest a n d �uriosity.


WHY LOOK? • The sta rs can tel l you time, d i rection, and position . These a re about their only p ractica l use to a n amateur. More impo rta n t is the sati sfa ction one finds in recogn izing the brig htest stars a n d p l a n ets. To see and to recog nize leo i n the eastern sky is akin to seeing the first rob i n . And, a s you learn more a bout the sta rs and the va riety of other celestial objects, the more the wo nder of t h e heavens g rows . WHERE TO LOOK • Sta r-gazing has n o geographic l imits. Some sta rs can even be seen from brig htly l it, smo ky city streets, but the less interfere n c e from l ig hts o r haze the better. AI"! ideal location is an open field, h i ll, or housetop w h e re the horizon is not obscured by trees or buildings. H owever, bui l d i n g s or a h i l l may a lso be used to screen off i n te rfering l ig hts, and althou g h you may see less of the sky this way, you will be a b le to see that part of it better. WHEN TO LOOK • O n ly the b rig hter stars and p l a n ­ e t s a re v i s i b l e i n f u l l moon l ig ht o r s o o n a fter sunset. At these times the beginner c a n spot them a n d learn the ma jor conste l l a tions, without being confused by myriads of fa inter sta rs . O n darker n i g hts, without moon l i g ht, o n e may observe m i n o r con stellations, fa inter sta rs, nebula e, a n d p l a n ets . Sta rs and pla n ets visible at a ny g iven hour depen d on time of ni ght a n d season of the yea r. As the ea rth ro­ tates, new stars come into view i n t h e eastern s ky a s the eve n i n g p ro­ g resses. late a t n i g ht o n e can see sta rs not vis­ i b l e i n the eve n i n g sky

until several months later. The 64-65, 72 -73, 82-83, 90-9 1 ) 1 24- 1 25) show the location of various times of the year. See

seasonal star charts (pp. and planet tables (pp. major celestial objects at check list, p. 1 58.

H OW TO LOOK • First, be comforta ble. looking at stars high above the horizon may cause a stiff neck and an ach­ ing back; so use a reclining chair, a couch, or a blanket spread on the ground. Remember-ground and air may be unexpectedly cold at night; warm clothing, even in summer, may be needed. How to look also involves a method of looking. The section on constellations (pages 50- 1 0 1 ) gives suggestions. After you have become fa­ miliar with the more common stars, constellations, and planets, a systematic study may be in order-perhaps with field glasses. By that time your, interest may lead you to some of the activities suggested on the following pages.

EQUIPMENT • You need no equipment, except your eyes, to see thousands of stars. This book wi ll point the way to hours of interesting obserxation with your eyes alone. later you will find your enjoyment greatly en­ hanced by the use of field glasses (6- to 8-power) such as those used in bird study. With these you can see vastly more-details on the moon, moons of Jupiter, many thou­ sands of stars, star clusters, double stars, and nebulae. larger field glasses ( 1 2-, 15-, or 1 8-power) will reveal- finer lunar details and more hundreds of ex­ citing stellar objects. Some day you may buy or make your own telescope.


ENJ OYING THE STARS • It i s worth repeating that night-by­ night o bservi n g studying, and enjoyin the stars is the activity that ca mean the most to most people. No equipment and little preparation are needed. This book Zeiss/ (see p. 1 58) and sources of infor­ Projection mation suggested (p. 1 1 ) will help. Planetarium ,

� t

IDENTIFICATION • The e n joym ent of sta rs involves some p ractice i n identificati o n . Knowin g two dozen con­ stellations and a dozen of the brig htest sta rs i s often enoug h . A syste matic study of sta rs, the identification of lesser con stellatio ns, and the location and study of clusters a n d n e bulae d e m a n d more i ntensive efforts . A serious amateur will ben efit by knowi n g n e a rly all the con stellations a n d bright sta rs before g o i n g deeper into any phase of a stro n omy.

• The planets, moving along in their orbits, are constantly changing their posi­ tions. Even the beginner can become familiar with the movements of planets-can recognize them, and predict which way they will travel. Knowing the planets is as im­ portant and as enjoyable as knowing the stars.


MUSEUMS • Many museums have astronomical exhibits worth seeing. These may include meteorites, photographs of stars and planets, and sometimes working models of


the solar system. Museums may be found at universi­ ties, observatories, planetariums , or governmental in­ stitutions. I nqu i re Hayden locally or when traveling concerning museums in the area that may offer astronomical exhibits.

• These are the sites of the great tele­ scopes and the places where professional astronomers work. When work is going on, astronomers cannot be dis­ turbed. But most observatories are open to the public at specified hours. Some offer a schedule of public lectures. OBSERVATORIES

PLANETARI UMS • I n New York, Chicago, Pitts burg h, Philadel phia, C hapel Hill (N . C . ) , Boston , Los Angeles and San Fra ncisco a re l ocated the l a rg e p rojectors that s how i m a g e s of stars and pla n ets on a da rkened d o m e . H u n ­ d re d s of people ca n watch these a rtificial stars w h i l e a lecturer poi nts them out a n d describes other features of the heavens . Many othe r p l a n eta rium s a re equipped with s m a l l e r but very effective p rojectors. CLUBS AND ASSOCIAT ION S

• Amateur astronomers often band together to share their experience and their interests. Clubs are found in most large cities and in many smaller ones. At meetings, a lecture or discussion is usually followed by a period of ob­ serving through telescopes. Some clubs work on co-operative projects in which the members share in some

scientific investigation . Visitors a r e usually welcome, a n d membership is commonly open to a nyone who is interested. Any person interested i n th e sta rs will en joy the activities described a bove. The th rill of knowing the pla n ets or visiting a pla neta rium can be shared by young a n d old alike. Th roug h suc h activities you may be­ come a serious a m a teur. The serious amateur may be a nyone from a youth in hig h school to a business m a n . Such a m ateurs spend much of Grinding a M i rror their time working on an a stron om ical hobby. They often become ex perts; some have m a d e i m ­ porta nt discoveries. Professional astronomers a r e gla d t o have the help o f tra ined amateurs, a n d several fi elds of astronom ical resea rch are m a n ned largely by them. Ama­ teur activities that demand g reater skill a n d experience offer g reater rewa rds in the satisfaction they provide to serious a mateurs. Here a re some: • Making a telescope req u ires time and patie nce. But in the end you have an instrument costing o n l y a small fraction of its worth, plus t he fun of having made it. The telescopes made by a m a teurs are usu­ a l ly of the reflecting type, with a concave m i rror instea d o f a lens for gathering lig ht. Telescope- m a k i n g k its, in ­ clud ing a roughly fi n ished g la ss "bla n k" for the m i rror, other telescope pa rts, and com plete i nstructio ns, are availa ble from some optical-sup ply firms. The final testi n g a n d fi nishing o f t h e m i rror require special skill a n d ofte n the he l p of someone with experie nce.



OBSERVI NG METEORS • Meteo rs o r shooti n g s t a r s (pp . 1 291 3 3 ) ofte n occur i n we ll-d e f i n e d s h ow e r s . C a reful o b s e rvation a n d plotti n g o f t h e paths of meteors yield info rmation of scie ntific value. Armillary Sphere Once Used to A n umber of Demonstrate Celestial Motions g r o u p s of a ma ­ teurs a re engaged in observi n g meteors, a n d a n y inter­ ested amateur o r g roup of amateurs c a n join. Contact the America n Meteor Society, 5 2 1 N . Wyn n ewood Ave ., Narberth, P en n sylva nia 1 9072 . OBSERVING VARIABLE STARS • Amateu rs with tele­ scopes have done u n u sual wo rk i n this adva nced field . Studies of these sta rs a re co-ordi nated by the American Association of Va riable Sta r Observers, 4 B rattle St., Cambridge, Massachu setts 02 1 00. The d irecto r of the Association will be gla d to fu rnish q ualified amate u rs with deta i l s a bout this work. STELLAR PHOTOGRAPHY

• Photographing the stars and other heavenly bodies is not difficult. Excellent pic­ tures have been taken with box cameras set firmly on a table. But pictures of faint objects must be taken with a telescope or with a special camera adjusted to compen­ sate for the earth's motion. Photography is an important tool of astronomers-one which the amateur can use to go od advantage.


MORE INFORMATION • This book is a primer to the sky a n d c a n only i n troduce a story w h i c h is more fully told in m a n y texts a n d popular books on a stronomy. BOOKS: Baker, Robert H., Astronomy, D. Van Nost ra nd Ca., New York, 1964. This col l eg e text is far the serious .tudent who wa nts d eta i l ed loch and modern theo r i es. Baker, Robert H., When the Stars Come Out, 1954, a nd Introducing the Constellations, 1957. V i k i ng Preu, N e w York. This pair of books serves to i n trod u c e the stars, meet i ng the n e eds of perso ns w ithout s c i e n t i f i c ba ckgrou nd. They are we l l i l l ustrated. Bernha rd , B e n nett, a nd R i ce, New Handbook of the Heavens, Whit­ t l es ey House, New York, 1954. A f i n e book, brid g i ng the g a p betwe e n pa p u l a r vol umes a nd texh. It stresses th i ngs t o d o a nd see. A lso i n a pocket edition by S i g net Books. Maya l l , Maya l l a nd Wyckoff, The Sky Observer's Guide, A Gold e n Handbook, Go lden Preu, New York, 1965. A n introd u ctory book for the laym a n with deta i l ed maps of the heave ns. O l cott, Maya l l , a nd Maya l l , Field Book of the Skies, G. P. Putn am's Sons, New York, 1954. The rev ised edition of a po p u l a r a nd p ra ct i c a l g u ide fo r the amat e u r observer.

PERIODICALS: Sky and Telescope. This is the outst a nd i ng magaz i n e for the amat e u r. Sky Publ ishi ng Co rp., 49-50-51 Bay Stale Road, Cambridge, Mau.



OUR U N IVERSE is so vast that its l i m its a re un k n own . Th roug h it a re scattered m i l l io n s of g a l a xies of various sizes a n d s h a p e s . In a g a l a xy l i k e o n e shown here (3 ) , our s u n a n d the ea rth are l ocated (see p . 4 2 ) . Ga laxies conta i n hundreds of m i l l io n s, even hun d reds of b i l l i o n s , of sta rs of m a n y types ( 1 ), ra n g i n g fro m r e d supe rgia nts


less d e n s e than the e a rth's atmosphere to wh ite dwa rfs h u n d reds of times d e n s e r tha n l ea d . Sta rs on the average a re spaced severa l l i g ht yea rs a p a rt; but there a re some clusters (2 ) , m ore closely packed towa rd the center that conta in perhaps half a m i l lion sta rs i n a l l . P l a n ets may revolve a ro u n d m a n y of the sta rs. 13

OUR SOLAR SYSTEM is l ocated ha lfway from the cen 足 ter of our g a l axy - the M i l ky Way. Aro u n d the s u n revolve the n i n e pla n ets with their 3 2 sate l l ites; a l s o h u n d reds of asteroids a n d swa rms of m eteors. Here w e s e e the p l a n ets ( 1 I i n t h e i r orbits a ro u n d t h e sun ( s e e p p .


1 02 - 1 0 5 ) a n d (2 ) in the order of their size. T h e asteroid Ceres i s co m p a red (3 ) to Tex a s for size, and the m o o n i s compared ( 4 ) t o the U n ited State s . A c o m et' s orbit (51 a p pea rs i n red . O u r solar system may b e only one of b i l l i o n s i n the u n iverse. 15

• Solar Prominences compared to Size of Earth

THE SUN ¡is the nearest star. Compared to other stars it

is of just average size; yet if it were hollow, over a mil l ion earths would easily fit inside. The sun's diameter is 860,000 miles. It rotates on its axis about once a month. T he sun is gaseous; parts of the surface move at different speeds. The sun's density is a l itt le under 1 Y2 times that of water. The sun is a mass of incondescent gas: a gigantic nuclear furnace where hydrogen is built into hel ium at a temperature of mil lions of degrees. Four mil l ion tons of the sun's matter is changed into energy every second. This process has been going on for billions of years, and wil l continue for bil l ions more. The sun's dazz l ing surface, the photosphere, is speckled with bright patches and with dark sunspots (pp. 22-23). Rising through and beyond the chromosphere, great prominences or streamers of glowing gases shoot out or rain down. The corona, which is the outermost envelope of gases, forms a filmy halo around the sun. It is unsafe to observe the sun directly with the naked eye or b inoculars. Use a special filter, a dark glass, or a film negative to protect your eyes. When a telescope is used, project the sun's image on a sheet of paper.



. .



Chromosphere Corona

How a Prism Breaks Up a Bea m of Sunlight into Its Component Colors

• Every square yard of the sun's surface is constantly sending out energy equal to the power of 700 automobiles. About one two-billionth of this, in the form of sunlight, reaches us. Sunlight is a mixture of colors. When it passes through a glass prism, some of the light is bent or refracted more than other portions. Light leaving the prism spreads out into a continuous band of colors called a spectrum. Colors grade from red, which is bent least, through orange, yellow, green, and blue to violet. whic h is bent most. The spectrum i6- crossed by thousands of sharp dark lines. These indicate that some light was absorbed as it SUNLIGHT

Frounhofer lines I nvisible Ultraviolet




passed through the cooler gases above the sun's surface. These gases absorb that part of the sunlight which they would produce if they were glowing at a high enough temperature. Thus a study of the dark lines in the solar spectrum (called Fraunhofer lines, after their discoverer) gives a clue to the materials of which the sun is made. Of the 92 "natural" elements on the earth, 61 have been found on the sun. The rest are probably present also. From the shifting of spectral lines, astronomers can meas足 ure the rotation of the sun and the motions of stars. They can detect magnetic fields from spectral lines and can determine a star's temperature and its physical state.




Invisible Infrared

RAINBOWS a re solar spectra formed as s u n l i g h t passes t h ro u g h d rops of wate r. Rain bows may be seen when a hose is ad justed to a fine spray. The d rops a ct l i k e pri sms, refracti ng s u n l i g h t to produce the s pectru m . A s i n g l e, o r prima ry, ra i n bow h a s red o n the outside, violet inside. The center of the a rc, 4 0 d e g rees i n ra dius, is a lways on a l i n e with the observer and the s u n . When you see a bow, the sun is behind you. Sometimes a seco n d a ry ra inbow forms outside the prima ry. It is fa inte r, with colors reversed - red inside, violet outside. The secon d a ry bow


forms from light refl ected twice with in drops. light may be reflected more than twice, so occasiona l ly up to five bows a re seen. Another type of bow- red, o r r e d a n d g reen - may a ppea r with p r i m a r y a n d secondary bows.

SUNSPOTS often a p pear on the s u n ' s p hotosph ere足

a p pearing as dark, sculptured "holes" i n contrast to the bright white surface. These sun spots ore sometimes so la rge they can be seen with the unaided eye (thro u g h a dark glass for p rotection, of course), a n d are most easily observed w h e n the s u n is low on th e h orizon . The use of field glasses or a small telescope h elps, but th e safest m ethod of observation is to study p hotog ra p h s . The dark ce nter, o r u m b ra, of a sunspot va ries fro m a few h u n 足 d red to o v e r 50,000 m iles across. This is surrounded by a less d a r k a rea, a penum bra, that often doubles the size of the sun spot. As th e s u n rotates, n ew suns pots come into view. Most persist for a wee k o r s o, but the maximum d u ration is from thre e to four months. The n u m b e r of sunspots varies i n cycles of about 1 1 years; first i ncreasing stead ily until h u n d re d s of g ro ups a re seen a n n u a l ly, then gradually d ecrea s i n g to a mini足 m u m of a bout 5 0 g roups . At the beg i n n i n g of a cycle the s u n spots a ppear a bout 3 0属 north a n d south of the sun's equator. As the cycle progresses, they develop closer to the equato r and the zone of a ctivity extends from 1 0 to 2 0 degrees o n either s i d e of it. Th e 1 1 -year

Relative size of earth

cycle is really an avera g e valu e . Myste riously waxi n g a n d wa n i n g , t h e exa ct length o f t h e cycle ca n be a s short a s n i n e years or as long as sixte e n . Some a stro n o m ers have pointed o u t that the 1 1 -year cycle seems to b e p a rt of a la rger 2 2 -year cycle in which the entire m a g n etic field of the sun may reverse itself. Sunspots seem to be gi a nt m a g n etic sto r m s on the sun's s urfa ce, which may b e cau sed by deeper, periodic changes. They occur i n g roups which g row ra pidly and then s lowly d e cli n e . The gases i n the s u n s pot (a bout 8 000°F) a re cooler than the rest of the sun's s u rfa ce (about 1 1 , 000°F); h e n ce they a p pear darker. Actu a l ly, if a la rg e s u n s pot could b e isolated i n a nother p a rt of the s ky, it would a ppea r a s bright a s a h u n d red full moons. Sunspots have stron g m a g n etic fiel d s . Rad iation from "sola r fla res" near them i nteracts with t h e u p p e r levels of the ea rth's atmosphere a n d interru pts short­ wave ra dio tra n s m ission; it is also likely to cause a n increase i n a u roras ( p p . 2 4 - 2 5 . ) 23

AURORAS OR NORTHERN LIG HTS • The shifting, g lowing, diffuse light of a n a u rora is hard to describe. Yel low, pink, and g reen lights come and go; a rcs of l i g ht start at the horizon and spread upward; strea m ers and rays extend toward the ze nith. Auroras last for hours, a n d often a l l throu � h the n ight. They a re seen in the north and middle northern latitudes and in the a rctic. A simi­ l a r display is seen in the southern latitudes. A uroras occur from about 60 to 600 m i les up i n the air. At these heights, so l ittle air remains that space is a lmost em pty like a


vacuum, or the inside of a neon light. The shifting glow of the aurora is essential l y electrical and somewhat similar to the light from the neon signs along Main Street. The sun's radiation on the rare gases of the upper atmosphere is what causes auroras. Auroras may be due to charged particles that come from solar flares near sunspots. The fact that auroras seem to center around the earth's magnetic poles emphasizes their electrical char足 acter. A few days after' a large new sunspot group de足 velops, an auroral display is likely to occur.


THE SKY FROM S UNRISE TO SUNSET • As the s u n ' s rays pass throu g h the earth's atmosphere, some a re scat­ tered, a n d a play of colors results. Blue rays are scattered m ost, and therefore a clea r sky is typically b l ue. Yel l ow rays a re scattered less than blue; thus the s u n itself, so lo n g a s it is well a b ove the horizen, looks yel l ow. But j ust after s u n rise a n d just before sun set the s u n is red d i s h . At these times the sha rply slanting sun's rays m u st trave l a longer path t h rough the atmosphere, a n d m o re of t h e blue a n d yel low rays a re scattered . The r e d rays, which a re scattered lea st, come through i n the l a rgest n u m bers, Sun light Pa11es T h r o u g h a Th icker l a y e r of Air at Sun rise and Sun set

giving the sun its reddish hue. If there are clouds and dust in the air, many of the red rays which fi lter d own into the lower atmosphere are reflected, and large areas of the sky may be reddened. Because of the bending or refraction of lig ht, which is greater when the sun is near the horizon, you can actually see the sun for a few minutes before it rises a n d after it sets. Daylight is a bit longer for this reason. The c loser to the horizon, the greater the refraction at sunrise or sun足 set. Hence, as refraction e levates the sun's disc, the lower edge is raised more than the upper. This distorts the sun, just as it is rising or setting, giving it an ova l or melon足 shaped a ppearance. Twi light is sun light diffused by the air onto a region of the earth's surface where the sun has a l ready set or has not risen. It is genera l ly defined as the period between sunset and the time when the sun has sunk 18 degrees below the horizon-that is, a little over an hour. 27

T H E TELESCOPE was fi rst put to practica l use by Ga l i leo in 1609. Since then, it has extended m a n 's h orizons farther and has chal lenged his th inking more than any other scientific device. The telescope used by Gali leo, the best足 known kind, is the refracting tel escope, consisti n g of a series of lenses in a tube. I n a simple refractor, two lenses are used, but com monly others a re added to correct for the bending of l ight that prod uces a col ored h a l o around the image. The la rgest refracting telescopes are one with a 40-inch lens at the Yerkes Observatory i n Wisconsin, a n d a 36-inch one a t lick Observatory i n C a l iforn ia .

The si m p le reflecti ng telescope has a cu rved m irror a t the bottom of the tube. This reflects the light in converging rays to a prism or diag足 ona l ly placed m irror, which sends the light to the eyepiece or to a camera mounted at the side of the tube. Since m irrors can be made larger than le nses, the largest astronom ical tel足 escopes are reflectors (see page 30). Reflec足 tors with m irrors up to 8

inches in d i a m eter a re m a d e by a m ateurs as the best sim ple, low足 cost telescope. A special type of reflector, the Schm idt, perm its ra pid p hoto g ra p h i n g of the sky and has become o n e of the m a j o r astro n o m ical tools. Also of g rowi n g i m po rta nce a re the ra d i o telescopes - gia nt, saucer-sha ped i n stru 足 ments which receive ra dio waves from outer space . Clouds of optically invisible n eutral hyd rogen, a b u n d a n t in the spiral a rm s of o u r gala xy, can be traced by their radio e m issions. Radio astronomy is a you n g science. 29

T H E LARG EST TELESCOPE of the refl ector type is on Palomar Mou nta in, near San Diego, Calif. Its 200-inch (16.6-foot) mirror is a marvel of scientific and e n g ineering ski l l . The great disc of pyrex glass was cast with support足 ing ribs to bea r its weight. It is 27 inches th ick a n d weighs 14J.-2 tons. Yet because of its design, every part is within two inches of the air-perm itting the m irror to expa nd and contract u n iform ly with changes in temperature. The great piece of g la ss has been polished to within a few m i l l ionths of an inch of its calc ulated curve. Despite its g reat weight it can be tilted a n d turned precisely without sagging as much a s the thickness of a hair. The m irror gathers about 640,000 times as much light as the h u m a n eye. With it, astronomers photograph stars six million times fa inter than the fai ntest sta rs you can see, a n d galaxies over two bil足 lion light years away.

S TAR S Stars are suns: heavenly bodies shining by their own light and genera lly so fa r away from us that, though mov­ ing rapid ly, they seem fixed in their positions.

NUMBERS OF STARS • On the clearest night you are not likely to see more than 2,000 stars. With changing seasons, new stars appear, bringing the tota l visible d u r­ ing the year to about 6,000. A telescope reveals m u lti­ tudes m ore. The tota l in our galaxy runs into bil lions, but even so, space is almost empty. Were the sun the size of the d ot over an "i," the nearest star would be a dot 10 miles away, and other stars would be microscopic to dime-size dots hundreds a n d thousands of m iles distant. DISTANCES OF STARS • The nearest star, our sun, is a mere 93 mil lion m i les away. The next nearest sta r is 26 mil lion m i llion miles-nearly 300,000 times farther than the sun. For these great distances, mi les are not a good me.a sure. I nstead, the light year is often used. This is the dista nce that light travels in one year, moving at 186,000 mi les per second: nearly 6 m i l l ion m i l l ion m i les. On this sca l e the nearest sta r (exc l uding the sun) is 4.3 l ight years away. Sirius, the brightest star, is 8.8 light years off. Other stars are h u n d reds, thousa nds, and even m i l l ions of l ig ht years away. 31

STARLIGHT • Al l sta r s shine b y their own light. This light may be produced by nuc lear reactions simi­ lar to those of the hydro­ g en b o m b . W h en t h e element hydrogen is trans­ formed into helium, which h a p pens on m ost stars, about 1 per cent of its mass (weight) is changed into energy. This energy keeps Antares Is Larger Than Mars' Orbit the te m p e r a t u r e i n t h e star's interior a t mil lions of degrees. At the surface the temperature varies from about 5,500 deg rees F. to over 55,000 degrees, depending on the kind of sta r. One pound o. f hydrogen changing to helium liberates energy eq ual to about 10,000 tons of coal. In a si ngle sta r the energy released in this way req uires the tran sformation of mil lions of tons of matter per second. STAR BRIGHTNESS • The sun is a bout avera g e i n s ize a n d brightness. Some stars a re up to 600,000 times as bright a s the sun; others a re only 1 I 5 5 0,000; most a re betwee n 1 0,000 a n d 1 / 1 0,000 times as bright as the s u n . The brig htness of a sta r you see d e p e n d s on its d ista n ce a n d on its real or a bsolute b rig htness. See pp. 34-3 5 . STAR SIZE • Most sta rs a re so d i sta nt that t h e i r size can o nly be measured indi rectly. Certa in giant red sta rs a re th e largest. Anta res ha s a d i a m eter 3 9 0 times that of the sun, others even l a rg e r. Among the s m a l l sta rs a re white dwa rfs, no la rg e r tha n p l a n ets . The s m allest a re n e utron sta rs that may be no more tha n ten m i l e s across.


D ENSI TY OF STARS • The densities or relative weig hts of sta rs va ry considera bly. Actually all sta rs a re m a sses of gas- but g a s u n d e r very d iffe re nt co n d itio n s from those we usually see. Giant sta rs such a s Anta res have a d e n s ity as low as 1 /2000 of the den sity of a i r. The more usual stars have a d en s ity fa i rly close to that of the s u n . W h ite dwa rfs a re so dense t h a t a pint o f t h e i r material would wei g h 1 5 tons o r more on ea rth. The co m p a n ion to S i rius is 2 5 , 0 0 0 times m o re dense than the su n . Neutron stars a re bi llions of times d e n ser. MOTI ONS OF STARS • O u r sun is moving a bout 1 2 m iles per seco n d towa rd the con stellation H e rcule s . Other sta rs a re movi n g too, at speeds up to 3 0 m ile s p e r second or fa ste r. Arcturus travels at 8 4 miles per seco n d . Many stars a re movi n g a s pcirts of systems or clusters . One such system, inclu d i n g sta rs i n Ta urus, is m ovi ng away at about 3 0 m iles per seco n d . Some stars co n sist of two o r m o re co mpon ents (see p . 3 8 ) which revolve a ro u n d a com m o n center a s t h e y m ove together throu g h spa ce . The sta rs i n a con stellation d o not n ecessa rily belong together; they may b e of widely d iffe ring d i sta n ces from the ea rth a nd may be moving in d ifferent d i rections at diffe rent speeds. COLOR OF STARS varies from b rilliant blue-white to d ull red dish, i n d icating sta r te mperature ( p p . 3 6 - 37) - a facto r in sta r cla ssification . Close observatio n is needed to see the ra n g e of colors in the n i g ht sky.

Brightness of Some Major Stars (above) and the Visible Planets (below)

STAR MAGNITUDES • Brightness of sta rs is measured i n ter m s of " m a g n itude." A 2 nd-mag n itude star is 2.5 times as bright as a 3rd, a n d so on throughout the sca le, so that a 1 st-m a g n itude star is 1 00 times as bright as a 6th. Stars brighter than 1 st magnitude have zero or m inus magn itude. On this sca le the m a g n itude of the planet Venus is -4; it is 1 0,000 times as b right as a 6th-magni­ tude sta r, which is the faintest that the una ided eye ca n see. The sun's ma gnitude is -27. The brig htn ess of a sta r as we see it depends on two factors: its actua l , or a bsol ute, brightness a n d its dista nce from us. If one factor is k nown, the other can be com­ puted. This relationship m a kes it possible to measure the distance of remote galaxies (p. 39).


THE BRIGHTEST STARS Constellation Name Sirius *Canopus *Al p h a C e n tauri Arcturus Vega C o pe l l o Rigel Procyon *Ach ernar *Beta Centauri Betelgeuse Altair *Alpha Cru c i s Aldebaran Spica A ntares Pollux Foma l ha u t Deneb Reg u l u s *Beta C r u c i s

C a n i s Major Carina C e n ta u r BoOtes Lyra Auriga Orion C a n i s Minor R i v e r Eridanus Centaur Orion Aqu i l a Southern Cross Taurus Virgo Scorpi u s Gemini Southern Fish Cygnus Leo Southern Cross

Magnitude as seen -1.4d -0.8 -{).3 d 0.0 0. 1 0.1 0.1 d 0.4 d 0.6 0.7 0.7 0.8 0.8 d 0.9 d 1.0 1.0 d 1.1 1 .2 1.2 1.3 d 1 .3


(light years)

9 540 4 32 26 45 650 11 140 1 40 270 16 160 68 230 410 34 23 1 500 86 470

A bso lute magnitude

+ 1 .5 -5.0 +4.1 +0.2 +0.6 -<l.5 -6.5 +2.7 -2.6 -2. 5 -4.1 +2.4 -2.7 -<l.6 -3.3 -4.0 + 1 .0 +2.0 -7.0 + 1 .0 -4.5

* Not v i s i b l e at 40째 N. lati tude. d D o u b l e stars: combined m a g n i t u d e g i v e n.


CLASSIFICATION OF STARS • Most of the sta rs you see can be c lassifi ed into seven groups accord i n g to the stars' s pectra. These, in turn, de pend ma i n l y on the tem­ perature of the ste l l a r atmosphere. The spectra of l ow­ tem perature sta rs show that some sim p l e chemical com­ pounds are present. As the tem peratures of sta rs increase, the s pectra revea l that fewer m o lecules occur, and that the atoms m a k ing u p the elements that are present be­ come excited and ionized. Ionized atoms a re th ose w h ich have l ost one or more el ectrons. On the basis of studies of thousands of spectra, sta rs a re a r ranged in seven c lasses: 0, B, A, F, G, K, and M. For more detailed study, astronomers divide each c lass into ten sub-classes, as AO, B3, or G5. Over 99 per cent of the sta rs fit into this classifi ­ cation. Four other classes (W, R, N , S) a re used for sta rs n ot fittin g the seven main g rou ps.



Star Approx. Temp. (degrees F.) cla ss


Spectral character



over 55,000

B l u e - w h i te

Gases stro n g l y ionized

I ota O r i o n i s ( i n sword )



B lue-white

Stro n g neutra l helium

Rigel Spica



W h i te

Hydrogen pred o m i n a n t

Sirius Vega


Yel l o w i s h w h ite

Hydrogen decrea s i n g; meta l s increa s i n g

Canopus Procyon



Yel l o w

Meta l s pro m i n e n t

Sun C a pe l l a



Ora n g e

Meta l s surpass h ydrogen

A rctu r u s A ldebara n




T i tani u m o x i d e p resent-v i o l e t l ight weak

Betelgeuse Antares



DOUBLE STARS • Over a third of a l l known stars are doub le, or "binary." The components of a few can be seen with the una ided eye; thousa nds can be "separated" with a tele­ scope; thousa nds more are detected by the s pectro­ scope. Some stars have three or more components; Pair af Double Stars: Castor Castor has six -three doub les. The main, m utua lly revolving pair was closest together in 1 968-about 55 times the distance of the ea rth from the sun. Mizar, at the curve of the Big Dipper's handle, has a fai nt companion. Miza r itself is a telescopic double and the brightest component is a spectroscopic double star. When the two stars are in line, the spectra coi ncide. When, as they revolve, one approaches us as the other moves away, the spectrum lines are doubled. Capella and Spica are also spectra l double sta rs. As double stars revo lve, one may ecli pse the other, causing re­ duced brightness. Best-kn own of ec lipsing double stars is Algol, in Perseus. It waxes and wanes at interva ls of about three days. The eclipsing sta rs are 1 3 m i l l ion mi les a part. Their combined mag­ nitude varies from 2.3 to 3.4. Triple

Star Syste m

VARIABLE STARS a re those that fluctuate i n b rig htn ess. Most d ra­ matic o re the explod i n g sta rs, or nova e . These d ense, white sta rs rapid ly g row in bri l l ian ce, up to 1 00,000 times or m o re, then fa de away. Other variables c h a n g e l ess d rastically regula rly or irregularly. Some red g i a nts and supergiants Nova of 1572 in Cassiopeia va ry from 4 to 1 0 m a g n itudes over a few m onths to two yea rs. M i ra, in C etus the Who le, is a fa mous l o n g -period varia b l e that shows extre me chan ges of brightness. The vari a b l es k n own as classical Ceph eids va ry i n b rig htn ess o v e r periods of o n e d a y to severa l weeks. T h e d ista nce of a n y o f these Cepheids con b e rea d i ly esti­ mated beca use of the defin ite relationship b etween its variation period a n d its a bsol ute m a g n itud e . By m easur­ ing the period, the a bso lute m a g n itude con be deter­ mined , and by comparing the a bsolute m a g n itude with the a p p a rent m a g n itu de, the d ista nce con be esti mated . These Cepheids a re im porta n t in the calcul ation of d is­ tances of sta r c l usters a n d g a laxies ( p p . 40-4 3 ) . I n recent yea rs, early i nformation about classica l Cepheids has ind icated that esti m ates of the d ista nces of g a l axies beyo nd our own should be at least tripled . Eclips1ng Binary, Algol, with Magnitude Changes

STAR CLUSTERS are groups of stars relative ly close to

one a n other and moving together as a stel lar system . C l usters are o f two types-open a n d gl obu lar. S o m e 300 o pen clusters occur in our galaxy (p. 42). Some are fine ob jects to observe with binocu lars (p. 158 ) . One c l ose wmoving c l uster" incl udes m ost of the stars in the Big D i p足 per. Another o pen cl uster incl udes a p proximately 150 stars in a n d around Ta urus, the Bu l l . Some open c l u sters are easier to recognize, as the Praese pe c l uster in Ca ncer, the Coma Beren ices c l uster, and the double c l uster of Perseus. Most open clusters are in or near the M i l ky Way. 40

Globular c lusters are much more compact, often more distant. The brig htest a ppear as dim, hazy spots; few ca n be seen with the unaided eye. About 100 have been found in c;>ur galaxy, and many more i n others. The g reat Her足 cules cluster M 13 (it was No. 13 in the astronomical cata足 logue of Messier) is striking in large telescope. It has half a million stars, at a distance of 34,000 l ight years. Its di足 a m eter is about 100 light years, but most of the stars are i n its "core," some 30 l ig ht years wide. There are 10,000 times as many stars in this c luster as in any equal space e lsewhere i n the sky. 41

OUR GALAXY A ND OTHERS â&#x20AC;˘ The sun, a ll t h e visible sta rs, a n d billions of sta rs seen o nly thr.o u g h a telescope form a huge, fla t spiral syste m k n own a s o u r g a laxy. This g reat sta r system is believed to be a bout 1 00,000 light ye a rs i n d i a m eter, but less tha n 7,000 light years thick a t our locatio n . O u r s u n is close to the e quatorial (lo n g ) pla n e of t h e galaxy, b u t well off to o n e side. The gal ac­ tic center o r n u cleus appea rs to be 26,000 lig h t years away, towa rd Sagitta rius (p. 77). Withi n the g a laxy a r e m a ny sta r clusters a n d g reat clouds of cosmic d ust. 42

Our ga laxy is rotati ng like a big whirl pool, a n d the myriads of sta rs move around its center somewhat as the planets rotate around our sun. Stars near the center rotate faster than those farthe r out. The two Mag e l l a n ic Clouds in the southern hemisphere sky, about 150,000 light years a way, a re the n ea rest ga laxies. They are sate l l ites of our system. Our ga laxy resembles the g reat spiral nebula M31 i n Andromeda-a galaxy some 2 million light years away a n d twice the size of our galaxy. Mi l lions of other g a laxies have been revealed by telescopes. 43

THE MILKY WAY forms a huge, irregular circle of stars tilted about 60 degrees to the celestial equator. Even before the structure of our galaxy was known, the great astronomer Herschel proposed that this concentration of sta rs was due to the ga laxy extending farther in space

in some directions than in others. It is now clear that in looking at the Milky Way you are looking down the long direction of our galaxy. As you look through a deeper layer of stars, the stars appear more numerous. The Milky Wa y has both thin and congested spots. In Sagittarius it is at its brightest, but all of it is a wonder to behold.


NEBULAE is a term (latin for "clouds") applied to dista nt hazy spots in the sky revea led by tele­ scopes. Many are remote ga laxies more or less like ours; others a re clouds of dust or gas withi n our gal­ axy. Of these closer nebulae, the brightest is the Great Nebula i n the sword of Orion-diameter 26 light years, dista nce 1,625 l ight years. The entire region of Orion has the fa int g low of nebu lae, but here the g low is stron gest. All such nebulae a re faint; only long-exposure photo­ graphs bring out details of most. Lum inous nebulae are found c lose to bright stars. Short-wave l i g ht from these stars stimulates the nebulae to g low like fluorescent lamps. The brig htest nebulae are associated with the hottest stars. Low-tem ­ perature stars d o not cause nebulae to fluoresce, but starlight scattered by the nebulae provides some i l l u­ m ination. Some nebulae, havin g no stars nearby, are dark. They may obscure brig ht parts of the Mil ky Way and be visible as sil houettes. A series of such dark nebulae divides the Milky ;• Way from Cygnus to Scorpius into two parallel bands. Most spectacu­ lar of dark nebulae (often called "coal sacks") is the Horse-head Nebula in Orion. Another is in Cyg­ nus near the star Deneb. ..

Quite odd-looking are the planetary nebulae, so named because they form loose "smoke ring s" around stars. The rings look something like the ex足 panding rings around novae, but the latter expand rapidly and dis足 appear relatively soon. Most planetary nebulae are very faint, even as seen through a telescope, but the Ring Nebula in Lyra, the Owl Nebula in Ursa Major, and others are spectacular as they appear in ti me-exposure photos such as those here.

Dust a n d gas, in the spiral arms of o u r g a l axy, m a k e it h a rd t o dete r m i n e colors, brig htness, a n d d ista nces of many sta rs. Dust m a k es sta rs behind it look red d e r, or may obscure them e ntirely. Brig ht gas clouds have h e l ped astronomers to trace the spiral a rms of our g a laxy. I n c re a s i n g ly effective in this work has been the use of radio telescopes, which receive "cl ues" i n the form of ra d io sig足 n a ls that h e l p to identify c h e m i足 cal com pou nds i n th e c louds.


THE ORIGIN OF STARS is a mystery, b ut the re lation

between spectra l c lass and a bsol ute brig htness of sta rs, as shown a bove, offers some clues. Sta rs evo lve out of cosmic gas. As they shrink a n d grow h otter, they may fol足 l ow the m a i n seq uence, as does our sun. Then, some as足 tronomers think, the sta rs begin to expa n d . H otter o n es expa n d m ost rapidly; some may sh ift over into the classes of the gia nts. F i n a l ly, as their substa nce is exha usted by radiation, stars may flash up in g reat explosions, becom48

>eclral Classes with Absalute Bri ghtness

i n g n ovae, a n d c o l l a pse. They may then become wh ite dwa rfs or n e utron stars and eventua lly cease to s h i n e . Astro n o m ers a re perplexed a lso by evid ence s u g g est足 i n g that the e n ti re u n iverse i s expa n d i n g ra pid ly. The m o re d ista nt cl u sters a n d g a l a xies seem to b e reced i n g at tre m e n d o u s s p e e d s . A t d i sta nces of o v e r a b i l l i o n l i g h t yea rs a re "quasars," o b j ects m u c h s m a l l e r, yet m u c h b rig hter, than ga laxies. Astron o m ers a re not clear a s to their exact nature . 49

THE CONSTELLATIONS Stars can be weighed and measured, and their brig ht­ n ess, color, a n d m oti ons have mea n i n g . Conste l lations a re d ifferent. They a re but figments of m a n 's imagination­ handy inventions to help map the sky. Some of these apparent patterns were known and used by our fore­ fathers for thousa n ds of years. Other minor conste l lations were invented by 1 7th-century astronomers. People in different parts of the world imagine the sta rs represent different sha pes a n d things. Most of the characters and ob jects of the constel lations we use come from the myths of the Greeks and Roma ns. A lthough they see m unchanged for a l ifetime, even a c�ntury, the conste l l a tions a re changing; the stars i n them are gra d u a l l y sh ifting their positions. I n a ny conste l l ation some sta rs may be farther away thqn others a n d u n re­ lated to them. They may differ in dir �'et�on of m ovement as we l l as color or spectra l c lass. Beca u s e of precession (p. 53), different sta rs have been and w i l l become the North Sta r. Many constel lations have been recog n ized since a ncient times. Their bounda ries were irreg u l a r a n d often v a g u e u n t i l astronomers fi n a l ly estab l ished them defi n ite ly by international agreement. Amateurs nevertheless learn stars m ost easi ly by using constel lations. Use the charts i n this section. Constel l ations near the north pole a re charted on pp. 54-55, and south circumpolar conste l lations on pp. 98-99. For midd le- lati­ tude conste l lations, you will fi n d a m a p for each of the four seasons, showing ma jor constel lations visible during that season i n the north tem perate zone. The dome of the heavens is hard to represent o n a flat m a p. The season a l m a ps are designed to show m ost ac­ curately constel lations i n midd i e n orth latitudes. Distortion 50

Big Dipper in 20th Century, with Sta rs Moving in D irection


A r rows.

is g reatest near the horizons a n d in the south. Constel la­ tion shapes are truer i n the 28 individ ual constel lation pic­ tures in this section. Here they a re upright. (For their positions relative to each other, see the seasonal maps.) Polaris i s a lways at about the north celesti a l pole; where it is n ot shown, an arrow freq uently points toward it. For a com p lete list of constel lations, see pp. 1 56- 1 57. Bright stars have names, often Arabic, a n d are labeled usua l l y in order of brig htn ess by Greek l etters and conste l ­ lation n a m e , a s Al pha Scorpii, brig htest sta r i n Scorpius, and Beta Cyg ni, second brig htest in Cygnus. Symbols are used in charts in this book a s fo l l ows: * Sta rs: 1 st magn itude (brig hter than 1 .5) ( 1 .5 to 2.5) 2d magn itude • • 3d m a g n itude (2.6 to 3.5) (fa inter than 3.5) 4th a n d 5th m a g n itude • Star c l uste rs a n d nebulae Big Dipper in




The term circu m ­ polar constellations implies that the ob­ server is somewhere between the equator and the pole. Each 24 hours, as the earth turns on its axis, the sky seems to wheel overhead. To an observer in the north temperate zone, stars near the pole remain in view as they swing around; stars near the equator rise and set. At the pole, all constellations are circumpolar; at the equator, none. For places between, the latitude is impor­ tant, for if a star or constellation is nearer to the pole than the pole is to the horizon, it becomes circumpolar and does not set. The bowl of the Big Dipper does not set at latitude 40 degrees north, but in Florida, at latitude 30 degrees, it does set and so is no longer circumpolar. When the sun is north of the equator during the summer, it becomes a circumpolar star north of the arctic circle. The circumpolar constellations are easy to learn, and you will find them the best place in which to begin your iden ­ tification of the stars . Once you know the Big D ip per, the rest fall into line. The Littl e D i p p e r, C a s s i o ­ peia, Cep heus, Draco, and Perseus will guide you to the other con­ stellations shown on the seasonal charts later in this boo k .

Besides rotating a n d revolv足 ing, the earth has an oscil lat足 i n g motion l i k e that of a spi n n i n g top d ue c h i efly to the pul l of the moon o n Earth's equatorial bul g e . Each o s c i l足 lation takes a bout 2 6 , 0 0 0 yea rs. Thus, the N o rth Pole t r a c e s a c i rc l e on t h e sky, pointing to d iffe rent sta rs' as it m oves i n its c i rcuit. Thus 3 ,000 years a g o A l p h a Draco n i s was the Pole Sta r. I n 1 4,000 A . D . Vega i n Lyra wil l b e the Pole Sta r a n d the other conste l l a tions will s h ift. accord i n gly. The Southern C ross w i l l then be visi b l e i n the n o rthern h e m is p h e re . 53


At about 40 degrees north latitude the fol lowing a re con ­ sidered circ u m po l a r constel l a­ t i o ns : Big Di pper (Ursa Major); L i t t l e D i p p e r ( U r sa M i n o r ) ; Cassiopeia, the Queen; Ceph­ eus, the King; Draco, the Drag­ on. To locate these constella­ tions, use the acco m panying chart. Facing north, hold the o pened book in front of you � so that the current month is l .. toward the top. The conste l l a .._ tions a re now about as you w i l l see them during the cur­ rent month at 9 p.m. To see how they w i l l a ppear earl ier, turn the chart clockwise; for a later time, counterc lockwise. A q ua rter of a turn wi l l show how much the positions of the stars w i l l change during a six­ hour period.




The fa m i l ia r Di pper is only pa rt of the Great Bear. The Dipper's seven sta rs are ea sy to fi n d if you face north on any clear nig ht. The two outer stars of the bowl point to the North Star, Polaris, which is about 30 degrees away. The dista nce between the pointers is 5 deg rees. Both measurements are useful in fi n d i n g your way a round the sky. The middle sta r of the handle (Miza r) is a double sta r. Its 4th -magnitude compan ion is faintly visible, if you look careful ly. The rest of the Great Bear s preads a s a curve ahead of the poi nters and i n another curve below the bowl. 56

URSA MINOR, T H E LITTLE BEAR ( LITTLE DIPPER) Pola ris, the Pole Sta r, is the ta i l sta r of the little Di pper足 a d i pper which has a reversed c u rve to the ha n d le. Polaris is a sun, q u ite l i ke our own , but brig hter. Its dista nce is about 50 l ig ht years. Polaris is not exactly at the pole b ut is less than a deg ree away; no other 2 n d - m a g n itude sta r is near it. It is commonly used by navigators to deter足 m ine latitude. Polaris is a Cepheid varia b l e which cha nges in magnitude very sl ightly every four days. The four sta rs in the bowl of the Little Dipper a re of 2nd, 3rd, 4th, a n d 5 t h m a g n itude, m a k i n g a good sca le f o r j u dging the brightness of nea r-by sta rs.


DRACO, THE DRAGON begins, il first, a bout 1 0 de足 grees from the Big Dipper's pointers, the two dippers. Then it swings aroun e Little Di pper, doub les back, and ends in a group of four stars, forming the Dragon's head. These are about 1 5 degrees from Vega i n Lyra . Thuban, in Draco, once the North Sta r, was the star by which the Egyptians oriented their famous pyramids. Though Draco is circ u m polar, it is best seen i n late spring and early summer, when it is highest above the northern horizon. A pla netary nebula in Draco can be seen with a sma l l telescope. 58

CASSIOPEIA a n d n ear-by Cepheus are involved in the myth of Perseus and Andromeda (pp. 80-8 1 ). Start at the Big Dipper, at the star where the handle and bowl m eet, a n d sight a l i n e through the Pole Star on to Cassiopeia . Cassiopeia has the shape of either a W, an M, or a chair, depending on how you look at it. Near the s pot m arked on the map a p peared the famous nova of 1 572. When this tem porary or explosive star a ppeared, it rapidly i n 足 creased in m a g n itude ti l l it w a s a s bright as Venus a n d could be seen in daylig ht. Within two years it faded from view.


CEPHEUS is closer to the Pole tha n Cassiopeia. The star, shown a bove near Cepheus' knee, is about 1 2 degrees from Polaris on a line with the star forming the end of the W of Cassiopeia. Cepheus is a five-sided fig ure, l i ke a crude, peaked house. Because of precession, the stars on the west side of Cepheus will successively become the North Star during the next 2,500 to 5,500 years. J ust south of the base of Cepheus is a garnet-colored sta r worth spotting with binoculars. Cepheid variable sta rs, used in measuri ng distances of ga laxies, are named from Delta Cephei i n this constel lation (see p. 39).


C i rcumpolar Sta rs as a Guide to Key Constellations

â&#x20AC;˘ Use the stars of the Big D i pper and other circum polar stars to l ocate o n e or two i m portan t constel l ations for each seaso n . Fol low the curve of the Dipper's handle to Arcturus, or a l i n e throug h the bottom stars o f the Dippe r t o Gemini. Trace from the end of the h a n d l e through the bottom of the bowl to leo. With these key conste l lations i n m ind, you c a n locate the others more easily. Be sure the conste l lation you are trying to l ocate is above the horizon at the season a n d hour you are looki n g . A K EY T O CONSTELLATIONS



The sta rs o f spring, summer, fa l l , a n d winter were se l ected as those easiest to observe at about 9:00 p.m. on the fi rst of April, J u ly, October, and J a n u 足 a r y . The seasons actua l ly beg in a week or so ea r l ier. Each night at the same hour, a star appears s l ig htly to the west of its former position. Hence stars seen in the east at 9:00 p.m. a ppea r higher a n d h i g h e r in t h e s k y at t h a t hour as the season advances. Before April 1 , spring conste l l ations are farther to the east, and far足 ther west after that date. latitude, as we l l as season and time of nig ht, determines star positions. The Pole Sta r's height a bove the horizon, for exa m ple, is the sa me as you r latitude. The seasonal m a ps a re for about 40 degrees north latitude. I n early spring, e leven 1 sf-magnitude sta rs are i n the sky at once. N o other season offers so m a ny. I n addition to the conste l lations on pp. 66-69, look for a n u m ber of sm a l ler ones. Between Gem ini and leo l ies Cancer, the Crab, a conste l lation of 4th- and 5th-mag nitude sta rs. At the center of Ca ncer, n ote the fuzzy spot. Field g l a sses or a sma l l te lescope brings out deta i l s of this open c l uster of some 300 stars; it is Praesepe, one of the nea r-by cl usters 62

i n our ga laxy. Another larger c l uster is Coma Beren ices, Berenice's H a ir. This is on a line between the ta i l star of leo a n d the e n d of the Big D ipper's hand le. Use fi e l d g lasses. In the southern sky are the fainter Corvus, the C row; C rater, the Cup; a n d Hydra, the Sea-serpent. Hydra sprawls below leo and Virgo, the Virg i n . It has one 2 n d足 m a g n itude star, the reddish A l phard. Corvus, a l o p-sided sq uare of 3rd-m a g nitude stars, is close to Spica i n Virgo (see p. 73). C rater is near by, south of leo. It has one 3rd足 m a gnitude star . South of Corvus is the Southern C ross. 63


About 9 p . m . i n middle north latitudes

::t 0



Face north. Hold open book overhead with top of page toward north. 65

GEMI N I, T H E TWINS are often considered wi nter stars, though they are sti l l high in the western sky at the first signs of spring. The bright stars Castor (2nd m a g n itude, white) and Po l l ux ( l st magnitude, yel l ow), mark the Twins' heads. They a re a scant 5 degrees apart, making good measuring points. Castor is a tri p l e star, and each of its three components is a double star (six i n a l l !). The bottom stars in the Big Di pper's bow l point in the direc足 tion of Castor. A line through Rigel a nd Bete lgeuse in Orion points to Pol l ux. The c l uster M35 i n Gemini is worth locatin g with g lasses.


LEO, T H E L I O N is the best k n own a n d most conspicuous Of the Zod i a n constellations ( p p . 1 0 0 - 1 01 ) . The Sickle, w h i c h clearly fo r m s the lion's head, is fou n d by fol lowi n g a l i n e throu g h the b a c k stars of the D i pper's bowl south足 ward . Regulus, a b l u e-white 1 st- m a g n itude star, 8 6 l i g ht years away, m a rks the base of the S i c k l e . The poi nters of the Big D i p p e r point in o n e d i rection to the North Star; i n t h e o t h e r d i rection, t o the tria n g l e t h a t ma kes u p the rea r of leo. The leon i d m eteqrs, a once-s pecta c u l a r g ro u p of "s hooti n g sta rs," rad iate fro m this part of the sky in m i d 足 Nove m ber.


BOOTES, T H E HERDSMAN is fou n d by fol lowi n g the curve of the handle of the Big Dipper 30 deg rees to bright, orange Arcturus. The other sta rs in Bootes are of 3rd a n d 4th m a g n itude. Most o f t h e m form a kite-sha ped figure extending c lose to the Dipper's hand le. Arcturus {mag颅 n itude 0.0), one of the few stars m e ntioned by 路 name in . the Bible, is a giant, a bout 24 times the sun's diameter, 32 light years away. Bootes is chasing the Bears with a pa ir of H u nting Dogs, whi!=h m a ke a sma l l conste l lation between Arcturus and the Dipper's bowl.


VIRGO, T H E VIRG I N begins as a Y-sha ped line of sta rs of 3rd a n d 4th magnitude extending toward Denebola, ta i l star of leo. Spica ends this group; it is a b l ue-white, 1 st-magnitude star 230 light years away. The rest of Virgo is a line of three stars extending on from Spica, a n d a para l lel l i n e o f three sta rs t o t h e north. I n Virgo is a cl uster of severa l h u ndred g a laxies about 1 4 mil l ion light years away. A few of the brig hter spiral nebulae can be seen with a sma l l telescope. Follow the curve of the Dip路 per's hand le through Arcturus to Spica.



A s Leo sinks into the west, a number o f new constella足 tions and bright stars move up in the east. Summer is fine for watching them. The weather is likely to be favor足 able and you may have more leisure. The summer sky is not so bril liant as the early spring sky. You a re not likely to see more than six 1st-magnitude stars. However, there are constel lations aplenty, and the Milky Way is most im pressive in summer. Bootes, the Herdsman, a late spring constel lation, is visible most of the summer, and Arcturus, found by fol足 lowing the curve of the Dipper's handle, is a good place to start exploring the summer sky. Rising just east of Bootes is the Northern Crown, Corona Borea l is. Then to the south comes Libra, the Sca les, a faint Zodiac con足 stellation. Farther south and east of Libra is Scorpius, the Scorpion, marked by the red, 1 sf-magnitude star Antares. Moving north again you can trace out the thin line of Serpens, the Serpent, and Ophiuchus, the Serpent-bearer. 1 he two constellations merge. A 2nd-magnitude star marks the head of Ophiuch us, but the remainder of both constellations are 3rd-, 4th-, and 5th-magnitude stars. This double star group has a midway position-midway between the pole a n d the eq uator and midway between the points where the sun a ppears on the first day of spring and fa ll. Sti l l farther north is Hercules, about due east of the Crown. East of Hercu les is a large triangle of 1 st-magnitude stars set on the Milky Way. These are landmarks for the late summer sky, when they are nearly overhead. The three 70

stars are Deneb in Cyg nus, the North­ ern Cross; Vega i n lyra, the lyre; and Alta i r in Aq uila, the Eagle. De­ neb is a bout 20 degrees east from Vega, and A ltair is a bout 30 deg rees from a l ine between them. South of Altair is Sag itta rius, the Archer. Part of it forms a Milk Di pper. Near the tria n g l e are sma l l b ut bright Del­ phin us, the Dolphin, and Sag itta, the Arrow. The southern summer sky in the reg ion of Sagitta rius is rich i n sta r c l usters and attrac­ tive faint stars. locating sta rs is easier if you estimate dista nces in deg rees. A circle conta ins 360 degrees; the d ista nce from the eastern to the western horizon throug h the zenith (overhead point) is 1 80 deg rees. From horizon to zenith is 90 degrees. The pointers of the Big Di pper are about 5 deg rees apart. From Denebo la, at the ta i l of leo, to the star at the top of the tria ngle is 1 0 degrees. From Rigel to Bete lgeuse in Orion is 20 deg rees. To avoid confusion as to which direction i n the sky is north, which is east, and so on, refer to the pole sta r. Thus, to find Sta r A, 1 6 deg rees "south " of Sta r B, draw an imaginary line from the pole sta r through Star B; then extend it 1 6 degrees. East a n d west a r e at r i g h t a n g les t o this l i n e . West is a lways the direction of a sta r's a pparent m otion as the evening prog resses. Any sta r ca n be exactly located on the celestial sphere by using the astronomical eq u ivalent of latitude (dec l i n a­ tion) and longitude (right ascension). Sta r atlases are made on this basis. large telescopes can be q u ickly directed towa rd a sta r wh ose position is know n . 71


About 9 p . m . i n middle north latitudes


Face north. Hold open book overhead, wit h top of page toward north.


H ERCULES lies, u pside down, just south of the head o t Draco. A line from Arcturus to Deneb in the N orther 1 Cross passes just n orth of it. A keyston e of four 3rd- a n . 4th-magnitude stars marks the center of Hercules. Along its western edge is the famous c luster M 1 3, 30,000 light years away, with half a mi l l ion stars. Through a telescope the cluster i s a rare sig ht. The solar system is moving to足 ward Hercules at 1 2 mi les per second. However, because of the rotation of our galaxy, the net movement of the solar system is toward Cygnus.


YRA, THE LYRE is a s m a l l conste l lation m a rked by the

lendor of Vega, its brig htest sta r. Blue-wh ite Vega , mag­ tude 0. 1 , 26 light years away, is the brig htest summer .:�r. Between the pair of 3rd-m a g n itude sta rs at the e n d ) f t h e d i a m o nd-sha ped conste l l ation is t h e fa med Ring \(ebula, 5,400 light years away (pp. 45-47). A large tele­ ;cope is needed to see its deta ils. One of the 3rd-ma gni­ ·ude sta rs in lyra is a b i nary star. The two sta rs ec l i pse �very 1 3 days, the m a g n itude dropping from 3.4 to 4.3, ·hen rising a g a i n . 75

â&#x20AC;˘ The fish hook shape of Scorpius in the southern sky is easy to identify. Antares, the red, 1 sf-magnitude sta r in the heart of the Scorpion, is a s u pergiant of a type that g ives out m uch m ore light than other sta rs in the same spectra l c lass. Antares' diameter is 390 times that of the sun, but its thin gases have a density of less than one-m i l l ionth of the sun's. It is 4 1 0 l ight years away and has a faint green com­ panion. Near Anta res and between the tai l of Scorpius and Sag ittarius a re severa l barely visi ble star clusters.



SAGITTARIUS, THE ARCHER l ies j ust east of Scor pius a n d fol l ows it across the sky. Its centra l pa rt, c a l led the Milk Dipper, is a sma l l , u pside-down di pper. Nea r the stars of the Arc her's bow a re severa l dark nebu lae. The genera l reg ion is rich in sta r c l u sters and nebu lae. The Milky Way is brightest here. A look at it with g lasses or a telescope is excitin g . Accord in g to m yth, Sagitta rius is s hooting the Scorpion which b it Orion, the H u nter, ca us足 ing his death. So Orion c a n not be seen when Scorpius and Sagittarius are i n the sky.


CYG N U S, THE SWAN is commonly cal led the Northern

Cross and actua lly looks like a cross. Deneb, at the head of the Cross, is in the brig ht triangle of summer stars. Albireo, a 3rd-magnitude doub le star, at the head of Cygnus, is almost on a line between Vega and Altair. The Milky Way splits here into parallel streams. The region is rich in varicolored stars-doubles and c lusters. It is a region worth exploring. A 5th-magnitude star in Cygnus was the first star measured for distance. It is one of the nearest- 1 0.6 light years away. With Vega and Altair, Deneb i n Cygnus makes a conspicuous triangle. 78


T H E EAGLE, THE ARROW, and T H E DOLPHIN are th ree neighboring conste l lations lying just south of the Cross and the lyre. Aq uila, the Eagle, is a large conste l 足 lation. Most conspicuous i n i t i s t h e b r i g h t star Altair (magnitude 0.8, dista nce 1 6 light years) with a star on e ither side. The rest of the constel lation m a kes a loose tria ngle pointed at Sagitta rius. Sagitta, the Arrow, a n obvious conste l l ation, l ies between t h e Eag l e a n d t h e Cross. Farther e a s t a n d forming a triangle with Aquila a n d Sag itta is D e l p h i n us, the Dolphin, or Job's Coffin, a s m a l l diamond of 4th-magnitude stars.



S o m e o f t h e a u t u m n constellations fol low s o c losely u pon those labeled "summer" that they can be see n wel l before there i s a n a utumn c h i l l i n the air. T h e a utumn conste l lations are not q u ite equal to the b ri l l iant skies of spring a n d sum mer. The constel lation patterns over l a p a nd hence a re n ot so c lear. T h e n umber o f bright stars is limited. But clusters, nebu lae, and some u n u s u a l sta rs w i l l entice t h e observer. Four of the autumn conste l l ations and two from the circ u m polar group (p. ·52) are drawn together by a famous Greek legend. No other legend is so wel l i l l us­ trated in conste l lations as that of the hero Perseus, the winged horse Pegasus, the king and q ueen of Eth iopia, and their fair daug hter Andromeda. King Cepheus a n d h is q ueen, Cassiopeia (both circ u m polar conste l lations), l ived ha ppily ti l l the q ueen offended the sea nym phs, who sent a sea monster (Cetus) to rava ge t he coast. The mon­ ster wou l d depart o n l y when the roya l princess Androme­ da was sacrifi ced. An dromeda was chained to a rock by the sea to await her doom. But j ust as the sea monster a p peared, so did Perseus, the son of J u piter, flyi n g with ' winged sandals. Perseus was returning home from a peril­ ous m ission. He had just succe�ded in killing the dreaded Medusa, a creature with such a terrifying face that m or­ ta ls who gazed on her turned to stone. (From the blood of Medusa, Pegasus, the winged h orse, h a d sprung.) After barga ining with the king, who prom ised his d a u g hter to the hero if he saved her, Perseus slew the sea monster Though the wedding feast was i nterru pted by a jea lous suitor, the pair l ived ha ppily thereafter. All the main characters of the Perseus legend are en­ shrined as conste l lations. Cetus, the sea monster, is a .•


s preading constel lation of dim sta rs. The five stars form ing the head of Cetus lie i n a rough circle southwest of the Pleiades and south of An­ dromeda. The conste l lation, extend­ ing south and west, has only one 2nd­ magnitude star, but a lso includes a famous variable sta r, Mira. Mira is a l o n g - period va ria b l e sta r ( p . 3 9 ) ; it was d i s covered in 1 5 96. like m a n y ot h e r l o n g - period va ria b l es, Mira is a red sta r with a spectru m that fits i nto C l ass M. W h e n at its d i m m est, Mira is an 8th - to 1 Oth - m a g n itude sta r wit h a te m p e rature of about 3 , 4 0 0 d e g rees F. S l owly, over a period of a ro u n d 1 2 0 d a ys, its b rig htness and te m p e rature i n cre ase ti l l it is between 2nd a n d 5 th m a g n itude, and about 4,700 d e g rees F . Then it slowly d i m s a n d cools. Other m inor conste l lations of autumn incl ude Tria ngu­ lum, the Tria ngle, a sma l l group just south of An dromeda between Pegasus and Perseus. About 7 or 8 degrees south­ west of the Tria ngle is Aries, the Ra m . look for a 2 nd-, a 3rd-, a n d a 4th-magnitude star in a 5-degree curve. Pisces, the F ishes, a V-sha ped group, fits around the southeast corner of the Square of Pegasus. The Northern Fish is a line of eight 4th- a n d 5th-magnitude sta rs. The Western Fish ends i n a sma l l circle of 5th- and 6th-magnitude sta rs just below the Square of Pegasus. Using the two western sta rs on the Sq uare of Pegasus as pointers, extend a line south nearly 40 degrees and you may see a bright sta r (magn itude 1 .2) close to the southern horizon. This is Fomalhaut, in the conste l lation of the Southern Fish. The rest of the conste l lation exten ds westward as a diamond­ sha ped group of 4th- and 5th -magnitude sta rs.



About 9 p.m. in m iddle north latitudes


Face north. Hold open book overhead with top of page towa rd north . 83

PEGASUS, THE WINGED HORSE is fou nd by extend足

ing a line from the Pole Sta r th roug h the west end of Cassiopeia. This line hits the eastern side of the great square-a rather i m perfect square about 1 5 deg rees on each side. West of the sq uare the conste l l ation extends towa rd Cyg n us and De lphin us. Pegasus is u pside down, with its head towa rd the equator. The 2nd-magnitude star A l p heratz, or A l pha Andromedae, is at the point where th e constel lations j oin. Pegasus was recorded as a con足 ste l lation i n ancient times. 84

A N DROMEDA in chains extends eastward from Pega 足 sus as two long, spreading lines of sta rs which meet at Alpheratz, a triple sta r (2.3, 5.4, and 6.6 magnitude). The northern line of stars extends toward Cassiopeia, the southern to Perseus. I n Andromeda is Messier 3 1 , the brig htest and la rgest of the spiral nebulae (pp. 42-43), visible to the naked eye (mag n itude 5.0). It is a bout 2 m i l l ion l ight years away a n d has a diameter of about 1 50,000 light years. Similar to our own galaxy in many ways, the Messier 31 is a bout twice as la rge.


PERSEUS lies close to Cassiopeia. A c u rved line of sta r! forming part of Perseus extends toward Auriga. Othe1 stars in Perseus comp.lete its roug h, K-sha ped figure. The downward side of the K points to the Pleiades. The up路 wa rd a r m ends with Algol, best k nown of the varia ble sta rs-the "Demon Star," or head of Medusa. It is a r ec l i psing bi nary. T h e brig hter sta r is t h ree times the diameter of our sun; the d i m mer, even l arger. As the: revolve, about 1 3 m i l lion mi les apart, the dim sta r ec lipse the bright sta r once every three days, causing a dro1 from 2.3 magn itude to 3.4.


AURIGA, THE CHARIOTEER is the last of the autumn conste l l ations, hera l d i n g the coming winter. Auriga l ies to the east of Perseus. A line drawn from the to p sta rs of the Big Di p per's bowl points close to C a p e l l a , a bright tri ple sta r ( m a g n itude 0. 1 ), farthest north of the 1 sf足 magnitude stars. Capella is sometimes k n ow n as The Goat; a near-by tria n g l e of sta rs a re the kids. Severa l open c l usters (M37 a n d M38 especi a l ly) a re fou n d i n Auriga. E a c h conta ins a bout 1 00 stars a n d is a bout 2 ,700 l ight years away. The m a i n part of Auriga is a five-sided figure of 1 st-, 2 n d-, and 3rd - m a g n itude stars.



The sky i s never clearer than on cold, s parkling winter nights. It is at those times that the fainter stars are seen in great profusion. Then the careful observer can pick out dim borderline stars and nebulae that cannot be seen when the air is less clear. The winter constel lations in足 c lude some of the brightest and easiest to recognize. Eight 1 st-magnitude stars are visible on January evenings, and you may see up to 1 1 by early spring. For the watc her of these faint stars the period of accom足 modation, or getting used to the dark, is important. You wil l need at least 5 or 1 0 minutes after looking at a brig ht light before your eyes wil l once again see the faintest stars. Use your star map first and then do your observa足 tion. If you use a flash light while observing, cover the lens with red cel lophane or with a sheet of thin paper to cut down the intensity of the light. Another good trick in view足 ing faint stars is to look a bit to one side and not direct ly at them. This side vision is actual ly more sensitive than direct vision. The winter constel lations center about Orion, the Great Hunter, who according to the Greek myths boasted that no animal could overcome him. Jupiter sent a scorpion which bit Orion in the heel , kil ling him. W h en Orion was placed in the sky, with his two hunting dogs and the hare he was chasing, the scorpion that bit him was placed there too, but on the opposite side of the heavens. The winter skies also include Taurus, the Bul l , of whic h the P l eiades are a part, and some minor star groups. Use Orion, so clear and easy to find in the winter sky, as a key to other near-by constel lations. The belt of Orion acts as a pointer in two directions. To the northwest, it points toward A ldebaran in Taurus, the Bul l, and o n,


past Aldebaran, towa rd the Pleiades. In the opposite direction, the belt of Orion points towa rd Sirius, the Dog Star. Sirius, Procyon (the Little Dog), and Bete lgeuse in Orion form a tri­ angle with equal sides about 25 de­ grees long. South of Orion, a bout 1 0 degrees, is lepus, the Hare; and an­ other 15 deg rees south is Columba the Dove (p. 96). A line from Rigel through Bete lgeuse points roug h l y i n the direction of Ge m i n i, th e Twins. With such stars as Betelgeuse, Aldeba ra n, a n d Rigel in the winter sky, it is worth reca l l ing that these represent an Arabian contribution to astronomy from the 8th to the 1 2th century. Arabian star names a re common. The Greeks, Roma ns, and their western Europea n descendants gave na mes to the conste l lations, most of which represent characters from Greek and Roman myths. Some of the sta r names are from the latin, too. Many of the ideas deve loped by the early astronomers have been d iscarded, as the lim ited observations of those days led to incom­ plete or wrong i nterpretations. But the names g iven to sta rs and conste l lations have often remained unchanged for centuries and are as useful now as they were long ago. Beca use winter nig hts are long, and often c lear, they offer a n exce l lent opportun ity for photogra phing sta rs and planets. The books l isted on p. 1 1 wi l l tel l you more about this i nteresting hobby. Sta r tra ils and photos show­ ing the movement of the moon or other pla nets can be .node with no equipment other than a camera. For other .<inds of photog raphs of heaven ly bod ies, a po lar axis, motor-driven with a clock, is needed to keep the camera accurately fol l owing the star or pla net. 89


About 9 p.m. i n m i d d l e n orth l atitudes


Face north. Hold open book overhead with top of page toward north. 91

ORION, THE H U NTER is conspicuous and easily remem足 bered. A line drawn from Polaris through Capella in Auriga wi l l bring you to Orion. So wi l l a line from the sta rs form ing the ends of the horns of Taurus, the Bu l l . j he recta n g l e forming the Hu nter's torso i s bounded by bright stars. Bete lgeuse is a red variab l e su pergiant (magnitude 0.7). Rige l, diagonal l y opposite but b l ue足 white, is a su pergiant double (mag n itude 0. 1 ) . F rom Orion's be lt, 3 deg rees long, hangs the faint sword, con足 ta ining the g reat nebula M42, a mass of g lowi ng gas 26 light years i n diameter and 1 ,625 l ight years away.


T AURUS, THE BULL represents the form J u piter took to

ca rry off Europa, a young pri ncess. (Only the forepart of the B u l l got into the sky.) Most conspicuous sta rs in Ta urus are the Hya des, which form its face. This c lear, V-shaped star group has Aldebaran, a red 1 sf-magnitude star, at one end. A l debaran is a double sta r 68 l ight years away. The Hyades, actua l l y a loose cl uster of about 1 50 stars, are about 1 20 light years away. From them exten d t h e horns o f Ta urus. T h e 2nd-magnitude sta r Nath, form足 ing the tip of the Northern Horn, is also part of Auriga and can serve as a g u ide to Taurus. 93

Pleiades as Seen with U n a ided Eye ( u pper left) and as Seen with Binoculars or Small Telescope

T H E PLEIADES are a part of Taurus, representing a s pot on the B u l l 's shoul der. They are an open c l uster of m a ny stars-at l east several hundred-wra p ped in a faint nebu足 losity. Seven stars are visib l e to the u n a ided eye. To count them is a test of good eyesig ht. Fie l d glasses show m a ny m ore. :rhis c l uster a n d the Hyades a re two open cl usters in which the sta rs can be seen without aid. According to the myths, this group of sta rs re presents the seven daugh足 ters of Atlas, the giant who su pported the world on h is shoulders.


CANIS MAJ OR AND MINOR are two conste l lations, each of which has a m a jor sta r. I n Canis Major (the Big Dog) Sirius, b rig htest of all stars, dominates. With a mag足 n itude of - 1 .43 it is over 300 times brig hter than the fa intest visib l e stars. Siri us, the Dog Sta r, is only 8.8 light years away. The rest of Canis Major i n c l udes double and tri ple stars a n d severa l c l u sters. Canis Minor, the little Dog, is s m a l ler and has only one visible sta r besides Procyon ( m a g n itude 0.4). The belt of Orio n points east足 ward and a l ittle south to Sirius. An eastwa rd line from Bete lgeuse i n Orion takes you to Procyon.


LEP US, T H E HARE and COLUMBA, T H E DOVE a re sma l l conste l lations near Orion. lepus is south of Orion and due west of Canis Major. The main port of the con足 stellation is a four-sided fig ure of 3rd- and 4th-magnitude sta rs. Most of the other stars a re between this g roup a n d Orion. The Dove, which commemorates t h e dove which flew out from Noah's Ark, is a n even smal ler constel l ation south of lepus and, i n most ports of the U nited States, close to the southern horizon . The fou r sta rs form a close group a bout 5 degrees long.



The fa rther south you go, the more southern stars you can see. At 40 degrees N. l atitude about h a lf the southern stars a re visible. I n south­ ern F l orida and Texas the Southern Cross is seen. Southern conste l ­ l ations n o t t h u s far de­ scribed are in a circle (next page) with i n 40 degrees from the South Pole. They were de­ scribed fi rst by Magellan a n d other early observ­ ers. Most famous is the Southern Cross, 6 de­ g rees long, pointing to the South Pole. The Cen­ ta ur, near by, has two 1 sf-magnitude sta rs. A compa n io n to one of them is the nea rest sta r to th e earth. T h e Magel­ l a n i c Clouds ( p . 4 3 ) a re close compa n i o n s of o u r g a l a xy. Right: Strip of Sky fro"' North Pole to South Pole


At a bout 40 degrees south latitude the follow­ ing are the chief circum­ polar conste l lations: Crux (Southern Cross), Carina (the Kee l, of the ship Argo), Volens (Flying Fish), Dor­ ado {Goldfish or Sword­ fish), Hydrus (Sea Serpent), Tuca na (Toucan), Octa ns (Octa nt), Pavo (Peacock), Ara (Alta r), Tria n g u l u m (Southern Triang le), a n d Centaurus (Centaur). At about the eq uator you ca n locate these constella­ tions with the accom pa ny· i n g chart. Facing south, hold the open book in front of you so that the current month is towa rd the top. The conste l lations a re now a bout as you will see them during the current month at 9 p.m. To see how they wi l l a ppea r earl ier, turn the chart cou nterclockwise; for a later time, clockwise. A q u a rter of a turn w i l l show how much the positions of the stars will change dur­ ing a six-hour period.

T H E ZODIAC is a belt of 1 2 constel lations: Aries, Ta urus, Gemini, Ca ncer, leo, Virgo, libra, Scorpius, Sag ittarius, Ca pricornus, Aquarius, Pisces. These star groups circle the sky close to the ec liptic, which is the g reat circle of the earth's orbit around the sun. The sun, moon, and planets look as though they move against the background of these constel lations and seem to be "in" them. Easiest to observe is the moon's path. The journeys of the planets ta ke longer, depending on their dista nce from the sun. The sun itself seems to move throug h the Zodiac con足 stel lations each year. The change of constel lations seen just before sunrise or after sunset confirms this movement.

1 00

Note, in the diagram, the earth circling the sun. From the earth, the sun seems to be in the conste l lation Libra. As the ea rth revolves, the sun will seem to move through Scorpius and Sagittari us, ti l l fi na l ly it is back i n libra again. Ba bylonians a n d other ancient astronomers recogn ized this apparent motion of the sun, moon, and pla nets. This knowledge h e l ped them predict the seasons. Nowadays the Zodiac is often l i n ked to astrology, which claims to interpret the infl uence of stars on people and worldly events. Astronomers are convinced that astrol ogy has no scientific foundation. 1 01

THE SOLAR SYSTEM There a re a ltogether in the sun's fam i l y 9 planets, 32 moons or satel足 l ites, thousands of minor pla nets or a ster足 oids, scores of comets, and u ntold m i l l ions of meteors. Centra l star of the solar syste m, the sun makes u p over 99 per cent of its mass (weig ht). The planets range from tiny Mercury, which is some 36 m i l l ion m i les from the sun, to farthest Pl uto. Mercury goes round the sun in three earth-months. Pl uto takes a l m ost 250 earth-years to circle the sun once. Around some of the planets revolve moons. A l though Merc ury, Venus, and P l uto have none, the other planets have one to 1 2 . J u piter, the la rgest pla net, has 1 2 . Of these, 4 can be seen with field g la sses or a sma l l telescope. The rings of Saturn, made of m i l l i o n s of tiny fra g 足 ments , c a n be seen i n a s m a l l telescope a s a p late l i k e b e l t a r o u n d the p l a n et. Most a steroids revo lve in paths between Mars a n d J u piter. T h e brig hter ones can be fou n d by a mate urs with telescopes if their positions a re known. Comets, circ l ing the sun i n elongated orbits, cruise i nto view a n d out again in periods ra nging from a few years to severa l h u n d red years a n d m uch longer. Meteors, which a p pear a s bright stre a k s o r flashes in the sky, b u rn because of frictio n with th e e a rth's atmos足 p here. Meteors that stri ke the e a rth p rovid e material fro m o uter space that one can study at fi rst h a n d . 1 02

Only on the e a rt h i s l i f e defi n itely k n ow n t o ex ist. Tempera足 tures on th e othe r p l a n ets e x c e p t M a rs a re pro b a b ly too ex足 treme to permit plant o r a n i m a l l ife a s we k now it. Ma rs, a s observed by Mari足 ner 9 space-probe i n 1 972, p ossesse s vo l c a n o e s, c a n yo n s a n d just possibly m a y be i n h a b ited by very simple l ife forms. P l a n ets out足 side our s o l a r syste m may exist.

THE PLANETS Average d i stance from s u n (in m i l l i o n s of m i l e s ) Distance from s u n {compared to earth)









1 .00




M a s s or w e i g h t (compared to earth}

0 .05


1 .00

Vo l u m e ( c o m p a red to e a r th )

0 . 06


1 .00



1 ,4 1 6




0 62

1 .00

I n c l i n a t i o n of equator to o r b i t ( i n degrees)




Weight of a n o b j ect w e i g h i n g 100 lbs. o n earth (in p o u n d s )



1 00

Diameter at equator ( i n m i l e s )

N u mber of moons

Length of d a y ( i n hours) L e n g t h of y e a r (compared to earth)










1 ,782



1 .52

5. 20

9 . 54

1 9 .19










318 . 4


1 4.5

1 7. 2



1 ,318















1 5. 7


1 .9




1 65










1 17


1 12

30 ( ?)


Laplace Theory of Origin of Solar System

O R I G I N OF THE SOLAR SYSTEM • The earl iest a n d m ost note"'!'orthy scientific expla nation o f t h e origin o f the solar system was developed by the French mathematician Pierre de La place i n 1 796. He imagined a g lobe of hot, g lowing gases in space, rotatin g slowly. As the g lobe con­ tracted, it rotated faster. The faster rotation caused the g lobe to flatten out i nto a disc, which, as it shrank, left rings of gas a round it. These rings gradu a l ly condensed i nto planets, some with sate l l ites. Laplace's theory, ca l led the nebular hypothesis, left many things unexplained a n d was grad u a l l y abandoned. Even today no theory g ives a wholly satisfactory explana­ tion of all the observed bodies a n d motions i n the solar system . Some modern astronomers, notably G. P. Kuiper, suggest that as the orig inal solar nebula shra n k, it may

1 06

have l eft d isti n ct clouds of gas rather than rings a round it. These c louds, called "protoplan ets, " condensed fu r足 ther a n d beca me the p l a n ets, with their atmospheres and satellites. The satell ites, it is bel ieved , could have formed by processes l i k e those that fo rmed the p l a n ets. People often i n q u i re about the possi b i l ities of other sol a r systems-of sta rs with p l a n ets, and p la n ets support足 i n g l ife . The n u m b e r of sta rs is so g reat that the statistical possib i l ity of other sola r systems does exist. Whatever the series of events that b roug h t o u r sol a r system into b e i n g , t h e y may h a v e been repeated m a n y times w i t h i n the tre足 mendous space of the u n iverse. la rge p l a n ets of a few nea rby sta rs may have been d etected, but n o system like o u rs has yet been d iscove red . Even with the n ewest telescopes the c h a n ces of seeing such a system are sl i m . A Modern Theory o f Origin o f Solar System

Artist's Conception of a Landscape on Airless Mercury

MERCURY, the s m a llest pla net and nea rest to the s u n , can at ti mes be s e e n i n t h e e a s t just before s u n rise o r i n the west just after sunset. It has p h a s e s l i k e the moon's ( p . 1 4 0 ) . Mercury orb its the sun every 8 8 days and rotates on its axis every 5 8 or 5 9 days. The d i rection of rotation is fro m west to east. The s a m e side of Mercury does not a lways face the sun, as once bel ieved, a n d so its te m p e rature is fa irly even rather th a n extremely hot on one side, cold o n the othe r .

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Venus in' C�escent Phase

VEN US, called the Morn i n g or Eve n i n g Sta r d e p e n d i n g on when it is visible, i s th e nea rest of the p r i n c i p a l p l a n ­ ets-a bout 2 6 m i l l io n m i les away at its closest a p p ro a c h . Then it a p p e a rs thro u g h the telescope as a thin c rescent. It is brig htest a month later- 1 5 times brig hter tha n Sirius, the brig htest sta r. A dense atmosphere c o n ceals the p l a n et's s u rfa ce, but its surface tem p e rature i s fa r a bove the boiling point of wate r. It rotates from east to west.

1 09

EARTH, the p l a net on which we l ive, g ives a basis for understa n d i n g the others . The earth h a s been accu足 rately measured . Its d i a m eter at the equator is 7, 9 2 6 . 6 8 m i l e s ; through t h e p o l e s it is o n ly 7, 899.98 m iles, o r 2 6 . 7 miles less. T h i s very s l i g ht flatte n i n g at the poles leaves the earth a n a l m ost perfect sphere. A n atmos足 phere of ga ses surro u n ds the ea rth, exte n d i n g u pward about 500 m iles. But the atmosp here decreases ra pidly with a l titude, beco m i n g thinner a n d thinner a s o n e goes higher. Half of it is found within 3 miles of the s u rface. The atmosphere is a n essentia l part of such effects as rai n bows, s u n rise a n d sun set colors, a n d a u rora s . T h e ea rth has a com p lex pattern o f motions, a l l o f which affect our re lationsh i p to the sta rs and other pla nets. First, the earth rotates on its axis in four min utes less than 24 hours as measured by your watch. Second, the ea rth re足 volves o n its 600- m i l l ion-mile orbit around the sun once a year, at a s peed of 1 8 \1 m iles per second. Third, the earth 's axis has a m otion, ca l led precession (p. 53), m a k足 ing one turn in a bout 26,000 years. Fourth, the North a n d South Poles a re n o t stationary, b u t wander in rough circles about 40 feet in diameter. Final ly, there is a solar motion of 1 2 m i l es per second, while our part of the ga laxy seems to be whirling through space at 1 70 m i les per second. The weig ht of the earth is written as 66 fol lowed by 20 zeros tons. On the average, it is 5\1 times as heavy as a n eq ual-sized body of water. However, studies of rock, of earthquake waves, a n d of g ravity show that the earth is not the same throughout. Near the center of the ea rth the m ateria l is under a pressure of about 25,000 tons per sq uare inch. That tremendous pressure creates a very dense core averaging about 1 0 to 1 2 times the weight of water. From the center of the earth to the surface is about


3,950 miles. The fi rst 2,200 is this dense, h eovy core of com pressed rock. The pressure couses this core to reoct like o liquid to eorthq u o ke woves. S u rrounding the core is o 1 ,700-mile rigid Ioyer of heovy rock which g rodes off into lighter rocks nea rer the surface. Finally comes the outer rocky crust, u p to 25 m i l es thick, where the den sity of the rock is only 2 .7 times thot of woter. On the very surface o thin skin o.f rock hos been altered i nto soi l by the oction of woter ond oir. It is here thot l ife is concentrated . 111

DAY AND NIGHT is due to the earth's rotation . The ea rth is a d a rk sphere l ig hted on o n e side by the s u n . As the ea rth rotates on its axis from west to east every 2 4 h o u rs, the sun s e e m s t o rise i n the ea st, c ro ss t h e s ky, a n d set i n t h e west. The earth's atmosphere bends a n d d iffuses t h e s u n l ig ht, before t h e s u n rises, t o m a ke dawn , a n d it keeps the sky l i g ht for a ti m e after the sun has set. Day a n d n ight are a lways equal at the equator, but because of the tiltin g of the earth's axis to the plane of its orb it, o n l y at the first days of spring and fa ll a re day a n d n ight equa l in middle latitudes . I n the n o rthern hemisphere, l e n gth of dayl ight and height of the sun a bove the horizon at noon increase fro m the first day of winte r to the first day of s u m m e r, then d ecrease a g a i n . The pola r reg ions h a v e 2 4 hour d a y s d u r i n g s u m m e r . 112

TIME â&#x20AC;˘ The earth rotates throu g h 3 6 0 d e g rees in a bout 24 hou rs, at the rate of 1 5 degrees per h o u r. New York C ity and lima , Peru, have the same s u n -time, because they have the s a m e l o n g itud e . But when it i s noon i n N ew York it is sti l l late morning in C h icago. When the sun reaches its hig hest point (noon) at a g iven location, the time at a point 1 5 degrees west of that location is only 1 1 o'clock. local time is therefore different for a l l places that are not on the same longitude. When o n ly loca l time was used, New York c locks were 1 1 Y2 m i n utes behind Boston, and Washington 's were 1 2 Y2 m i n utes behind N ew York. To avoid the confusion resu lt­ ing from such sma l l differences, in 1 883 the nation was divided i nto time belts, each about 15 deg rees wide a n d e a c h differing b y o n e h o u r i n time. S i m i l a r belts n ow girdle the earth-24 of them.

Position of Sun at Sunrise, Noon, and Sunset in Middle Northern Latitudes EARTH SEASONS • Beca use of the 23Yl-degree tilt of the earth's axis, the sun is above the h orizon for different lengths of time at different seasons. The ti lt determines whether the sun's rays strike us at a l ow a n g l e or more di rectly. At New York's latitude the m ore nearly d irect rays on J u n e 22 bring about three times as m u c h heat as the more slanting rays of Decem ber 22. Heat re­ ceived by any reg ion depends on len gth of daylight and angle of the sun a bove the horizon . Hence the differ­ ences in seasons in different pa rts of the wor l d . I n t h e region within 23V2 degrees o f the poles. t h e sun remains above the horizon 24 hours a day d ur­ ing some pa rt of the sum mer. The farther north, the longer it stays a bove the h orizon. Every place a bove the a rctic circle experiences the m i d night sun. In the area within 23V2 degrees of the eq uator, the sun is overhead at noon at some time during s u m mer. For latitudes i n be­ tween, the hig hest point reached by the sun in summer is 90 degrees minus the latitude, plus 23V2 degrees. The low point of the noonday

1 14

at Beginning of Each Season

sun, in midwinter, is 90 degrees minus the latitude, minus 23Y2 degrees. At C h icago (latitude 42 degrees north) the height of the noonday sun varies from 24 degrees in winter to 71 Y2 degrees i n sum mer. loca l conditions affect seasonal patterns. Mou nta in ran ges, ocean c urrents, a ltitude, preva i l i n g winds, and other factors produce the seasonal c l imate in a g iven loca l ity. But the a n g l e of the sun's rays is sti l l a most im颅 portant factor in determ ining the plant, a n imal, and human l ife i n a region. Positions 路of Midnight Sun at I S-Minute Intervals above the Arctic Circle

MARS ci rcles o u r sky i n j u st u n d e r two yea rs as it revolves a ro u n d t h e s u n i n s o m e 6 8 7 d a y s . I t moves i n a n eccentric orb it; sometimes it i s 3 5 m i l l ion m i les f r o m u s , s o m e t i m e s 2 3 4 m i l l ion m i l es. The positions best for observation occur every 1 5 o r 1 7 years (Octo ber 1 973 was last) . Fl ybys of Mars by M a r i n e r probes s howed the s u rfa ce to be Shrin kage of a P o l a r C a p (tilted to路 ward earth) During a 3-Month Period

:> v a l tabl e l a n d n e a r south p o l e of Mars; p h otog r a p h e d by M a r i n e r



covered by craters created by asteroidal impact ranging from several hundred miles to a thousand feet. The sur­ face shows a striking similaritiy to the moon. No canals were found. The reported canals of the past century's observations were made up of unrelated dark spots put together as continuous features by the observer's eye and mind. The polar caps are real and probably are made up of a mixture of snow and dry ice. The atmosphere is largely carbon dioxide. Temperatures may reach 60 ° F in the day time and - l 00 ° F at night.

1 17

J U PITER is the l a rgest p l a net. N ever closer than 367 m i l l io n m i les to earth, it ta kes 1 2 of our yea rs to circle 路 the Zod iac. Light a n d dark belts p a ra l lel to the equator, i n the p l a n et's atmosphere , slowly c h a n g e . The g reat red spot, 3 0, 000 miles long, seems more nearly perma nent, though fad i n g . Four o f t h e moons, large a n d bright, have dia meters of 2 ,300 to 3,200 mi les. They revolve a round J u piter in 2 to 1 7 days a n d may easily be seen with field g lasses. Often one or more a re ec l i psed by J u piter or pass before

1 18

it, th rowing sma l l shadows on the c louds. The other eight moons are l ess tha n 1 00 m i les in diameter. One, very close to Jupiter, revolves at over 1 ,000 mi les a m i n ute. J u piter, fastest-rotating of the planets, turns in less tha n 1 0 hours. This speed has produced a pronou nced flatte ni ng at the poles. The temperature of J u piter is close to minus 200 degrees F . Ammonia and methane gases are i n the atmosphere, but no water. Ice may exist on its cold, barren surface. 1 19

SAT U R N is a bright "sta r" to the unaided eye, b ut its rings can be seen only through a telescope. The c losest it gets to the earth i n its trip around the sun, which takes 29 of our years, is 7 45 m i l l ion m i les. It stays two years i n each constellation o f t h e Zodiac. Like J u piter, i t is cov足 ered with banded c louds. The bands are not so c lear as J u p iter's b ut seem more nearly permanent. Bright spots occasiona l ly a ppea r in them. The rings were discovered in 1 655 by telescope. They a re probably made of very many sma l l solid particles.

1 20



of Its Moons

These may be materi a l which n ever formed into a sate l l ite, or frag ments of a close satellite torn asunder by the tidal p u l l of Saturn, or ice partic les. F i rst is a du l l outer ring, n ext a dark a rea, then the wid est, brig htest ring, a n d i n足 side this a thin, dark space and a dusky "crepe" ring. This inner ring is thin and quite transparent. The rings shine brightly, and when they are ti lted toward the ea rth, Saturn's brig htness increases. Outside the rings a re ten moons. One, la rger than ours, is the on ly satel l ite be足 l ieved to have an atmosphere. 121

Photographic Plates by Which

URAN US, NEPTU NE, and PLUTO â&#x20AC;˘ Ura n u s may be seen by a sharp-eyed observer. The other outer planets are telescopic. Uranus was accidenta l l y discovered i n 1 78 1 . Its failure t o fo l low its predicted orbit seemed t o be due to the gravitationa l p u l l of a pla net farther out. Two astronomers i n dependently calculated the position of the undiscovered planet, and when telescopes were turned to this region in 1 846, Neptune was found. Pl uto was discovered in 1 930 at the Lowel l Observatory as the suc­ cessful conclusion of a search over many yea rs.

1 22

ASTEROIDS â&#x20AC;˘ The 1 , 700 m i n o r p l a n ets now k n own are all telescopic objects. Most of them were d iscovered p h otog ra p h ica l ly. The l a rgest, Ce res, has a d ia meter of 480 m i l es. M ost of the rest a re less than 50 m i l es wid e . The m a j ority m ove between the orbits of Mars a n d J u piter. Others e n t e r the a rea between Ma rs a n d the su n . Eros, one o f these aste roids, will be wit h i n 1 4 m i l l i o n m i l es of the ea rth i n 1 975 . Most fa m i l ies o f aste roids seem stro n g l y influenced by J u piter, and m ove i n orb its determined by the g ra vitati o n a l p u l l of J upiter a n d the su n .

1 23


The tables on these pages w i l l help you locate the best-k nown planets i n the conste l lations where they w i l l be found at various times. T h e constellations are those of the Zodiac (pp. 1 00- 1 0 1 ) . Positions indicated a re a p足 proximate. To be sure of not m istaking a star for a planet, check a ppropriate constellation charts if necessary. For pos itions of Merc u ry, Uranus, Neptu n e , a nd P l u ta , ref e r Ia Ameri足 can Ephemeris and Nautical Almanac or a t h e r yearly aslra nam i c a l hand books, a r I a Sky and Telescop e maga z i n e. Italic type i n d icates morning sta r; reg u l a r type i n d ic a tes evening star. Dashes i n d icate p l a n e t is too near Sun for o bservatio n . ( S o u rc e : P l a n e t T a b l es b y F r e d


W h i p ple)






1 975

C a p r i corn us


1 976 1 977 1 97 8 1 979 1 9 80

Op hiuch us A q u a r i us

Pisces Aries



C a p r i corn us

Tau rus


Lea Li bra

Taurus Leo

Virgo l i b ra

Tau rus


Path of Saturn

1 970- 1 9 8 5

Venus in Leo, J uly 1 978 1 975


1 976

Tau r u s

1 977 1 978


1 979 1 980

Cancer Leo

Mars in Gemini, April 1 976 MARS Aquarius



Gem i n i


V i rgo





l i bra





V i rgo


Ca n ce r


1 975 1 976

A q ua r i us P i s ces





1 977 1 978 1 979


Tau rus




Gem i n i





Ca n ce r


1 980





1 975

Gemi ni

Gem i n i

1 976


Gemi ni

1 977 1 978 1 979 1 980


Ca n c e r

C a n cer


Leo Leo

leo Leo

leo L eo

Leo Leo





SAT U R N Cancer Cancer

Path of Halley's Comet

COMETS appear five to ten times yearly. Most a re fa int telescopic objects, but the chance of seeing at least one l a rg e, bright comet d u ring you r l ife i s good . Records of com ets, w h i c h often caused terror i n a n c ient times, go b a c k at least 25 centuries. The fa mous H a l l ey's comet was reported a s long ago as 240 B . C . Comets a re a m o n g the s m a l l e r m e m bers o f the solar syste m , m ov足 i n g a round the sun in definite o rbits. Most have orbita l periods of tens of thousa n d s of years. Com ets seem to be cl osely related to m eteo rs and perhaps to a ster足 oids . The head of a comet may consist of ice a n d m eteoric p a r足 ticl e s . Many com ets a n d m eteor swa rms have s i m i l a r orbits . A few c o m ets have not rea ppea red as 1 26

Path of Encke's Comet

Halley's Comet, Morning of May 1 3, 1 9 1 0

pred icted , b u t i n stea d , meteor showers have occurre d . Com ets s h i n e partly by refl ected l i g ht , pa rtly because sun l i g ht causes their own gases to g l ow. Comets' ta ils consist of exceedingly fi n e gases a n d dust, expe l led from the heads of the comets. The tai l may be so tenuous that sta rs shine through it with u n d i m i n ished b r i g h tn e s s . ( T h e e a r t h h a s passed through the tai l of H a l 足 ley's comet with n o a p parent effect.) A comet's ta i l a lways strea ms away from the sun, a n d as the comet recedes from the sun the size of the tai l de足 creases. Most comets lack a s pectac ular tai l ; i n others it develops rapidly a n d may be足 come h u ndreds of m i l l ions of miles long. Effect o f S u n '-s Rays on Tail of Comet


M.qU S


H a l l e y' s- Last seen i n 1 9 1 0. N ext expected a bout 1 986. The o n l y conspicuo u s comet that retu rns i n less than 1 00 yea rs. I t h a s been ob足 se rved on 28 retu rns.

Sept. 1 8 82-A b r i l l i a n t comet, disru pted afte r passin g close to the s u n . Split into four comets, which may retu rn between 2500 a n d 2 800.

Biela's- l n 1 846 this comet s p l it. In 1 852, twi n comets retu rned on t h e s a m e orbit. I n 1 872 a n d i n 1 885, the comets failed to retu r n but b r i l l i a n t meteor showers w e r e seen i n stea d . Encke's-A sma l l telescopic c o m e t of J u piter's fa m i l y . It has retu rned reg u l a rly since 1 8 1 9 at 3 . 3-year i nterva ls. Schwassmann-Wach ma n n-This comet, d is足 covered in 1 925, h a s an orbit which l ies entirely between the orbits of J u pite r and Satu rn, g iving it the path of a p l a net.

Left: Great Camet af 1 843

METEORS are genera l ly stony or meta l lic particles which become sepa rately visible when they plunge into our at­ mosphere. Though 1 00 m i l lion or more stri ke the earth's atmosphere dai ly, those l a rger than dust particles va por­ . ize. Occasiona l larger pieces penetra te th e atmosphere and strike the earth. Meteor frag ments that reach the ground a re known as meteorites. They vary from b its hardly larger than dust particles to c h u n ks weig hing tons. The average meteor is estimated to weig h o:-ooo s ounce. The two l argest known meteorites were fou nd i n Southwest Africa (Hoba mete­ orite) a n d Green l a n d (Ahnigh ito meteorite). Both are from the nickel-iron type of meteor. Another type, the stony meteor, is sma l ler or is broken u p more i n fa l ling. N o stony m eteorites larger than a bout a t o n h a v e b e e n fou nd. Near Winslow i n Arizona, east of H udson Bay, a n d i n Siberia a n d Esthonia are l a r g e craters made when giant meteors struck the earth. Small meteorites have been found near the Arizona crater, but the giant one, esti­ mated at over 50,000 tons, has never been discovered. It probab l y va porized on its i m pact. Meteorites a re often covered with a sm ooth black crust formed as the tremendous heat ca used by the fric­ tion of the air fused the meteor's surface. I nside, the 1 29



Jan. 2-3

Q u a d r a n tids

Location of Radiant E

Between Bootes a n


heod of Draco NE

Between Vega a n d Hercules

Apr. 20-22


May 4-6


Aug. 1 0- 1 3


Oct. 8 - 1 0 -

D raco n i d s


B r i l l i a n t in 1 946.

Oct. 1 8 -23



Between Orion a n d Gem i n i

Nov. 8-1 0


Dec. 1 0- 1 2

G e m i n ids


SW of t h e S q u a re of Pegasus



rse u s Period a b o u t




Between Ta u r u s, Auriga, and Perseus


N e a r C a stor in G e m i n i

La rge I ron Meteorite f r o m Greenland: 3 4 Tons

Meteor Crater, Arizona

meteorite either is stony or is com posed of iron-nickel a l loys, which usua l ly show pec u l iar crysta l patterns. I n a l l , a b o u t 30 chemical elements have b e e n fou n d i n meteorites. Meteors may be seen o n a l most any clear nig ht, though they are more com m o n in the hours after mid足 night. An observer can usua l ly see about 10 per hour. Occasionally g reat m eteor showers fill the sky with celes足 tia l fi reworks. These are rare, but lesser showers of me足 teors can be seen periodica l l y Stony Meteorite d u r i n g t h e y e a r . S o m e 600 "streams" of m eteors are bel ieved to exist, but o n ly a few provide s p ecta c u l a r s h o w e r s t h a t t h e a mateur c a n count on seeing.


Amateurs w h o know t h e stars and conste l lations c a n study a n d m a p meteor showers. Most are best seen be­ tween midn ight and dawn on nig hts when showers are expected. Observation works best when two or more ama­ teurs co-o perate. Several observers faci n g i n different directions can thus cover the entire sky, and few meteors escape notice. When possible, each observer should have a n assistan t to record the data, beca use meteors may sometimes come so fast that one cannot ta ke time out to record them. For each meteor observed it is im porta nt to record the timei the star and conste l l ation near which it is fi rst seen ; its direction; and the length of its path, in de­ g rees. Notes on its speed (meteors vary considera b ly), color, trail, and bril liance as com pared to stars of known mag nitude are a lso worth while. Prepare data sheets i n advance. Deve lop abbreviations for q uick recording. Find a place with a clear view of the sky a n d arrange for deck cha irs or some other com­ forta b l e rest. Warm clothing and a b l a n ket, even i n sum­ mer, are a dvisable. Amateurs have recorded h u n d reds of meteors in a n hour of observation. Each, plotted on a chart of the sky, g ives a picture sim i l a r to that on the n ext page, clearly in dicating the radiant point of the shower.

Perseid Shower Noted on American Meteor Society Chart • This is a chart of the paths that meteors seem to fol low during a shower. Actual ly, the meteors move i n para l le l paths. These paths seem to emerge from a point-a n optical i l l usion due to perspec­ tive. Meteors i n a shower do originate i n the sa me part of the sky, though they are not related to the constel l a­ tion from wh ic h t h ey seem to come. If t he radiant point and the speed of the meteors are known, the orbit of the meteor swarm can be ca lcu lated. The more observa­ tions, the more accurate ly this can be done. Possib l y most meteors belong to swarms and very few sol itary, stray meteors exist.


1 33

ZODIACAL LIGHT is so c a l led beca use the tria n g u l a r band of l i g h t w h i c h extends f r o m t h e horizon h a lf way to the zenith fol lows the earth's ecliptic and hence passes through the conste l l ations of the zodiac. This faint g l ow足 ing light is best observed in the ea rly evenings of March a n d April and just before dawn in September and Octo足 ber. In the tro pics it is seen more often. On a clear, moon l ess night its brig htest a reas may outshine the Milky Way. In the above i l l ustrations its brig htness has been e m pha sized to show its form. Zodiaca l light is a p parently sun light refl ected from meteoric partic les existing i n areas near the plane of the ecliptic. Though meteoric particles a re concentrated in

1 34

this reg ion, they are widely separated . If the pa rticles were of pinhead size and five m i les apart, there would be enough within the ea rth's orbit to reflect the amount of light usua l ly observed. The zodiaca l light seems to widen into a spot some 1 0 degrees i n diameter at a place j ust opposite the s u n . This faint haze of l ight that moves opposite the sun is known as Gegenschein or Cou nterg low. The area of zodiacal l ight cal led Gegenschein may owe its increased l ight to the fact that meteoric particles di足 rectly opposite the sun reflect towa rd us m ore s u n l ight than is refl ected by partic les in port i ons of the band that are not direct ly opposite the sun. 1 35

ON T H E M O O N â&#x20AC;˘ Our u n i q u e moon is ove r a q u a rter of the d ia m eter of the pla net a ro u n d which it revolves. However, its wei g h t is o n l y 1 /8 3 that of the earth, its vol u m e 1 /50, a n d its g ravitational p u l l l /5 of the e a rth's. No l ife forms have been fou n d there. O n the su n ny side, tem p e ratu res a re near b o i l i n g ; on the dark sid e they a re lower than a ny o n eart h . I n so me sections c i n d ery, d usty p l a i ns exte n d in a l l d i rections, their surface m a rred by deep cracks a n d b roken ridges. Thousa n ds of craters, som e ca used by meteors, so m e perhaps by a n c i e n t volca-

1 36

E a rt h ri s i n g over l u n a r h o rizo n ( N A S A l

noes, cover the rest of the moon's surface. Th ese ra nge from 14 mile to 1 50 m i les across, with steep, rocky wa l l s jutting u pward a s h i g h a s a m i l e or two. Someti mes a n iso足 lated pea k is within the crater. Bright streaks or rays extend in a l l directions from some craters. Besides the craters and plains (ca l led seas by early astron omers who thought they were fu l l of water), the moon has mountain ranges with pea ks th ree, four, and five m i l es h igh. I n proportion to the size of the moon, they are m uch h igher tha n mountains on the earth. 1 37

ROCKET TO THE MOON • When the first artificial earth satellites were successful (Soviet, October 4, 1 957; U.S. February 1, 1 958), experts predicted that rockets capable of reaching the moon would soon be developed. Speeds of about 7 miles per second, or 25,000 miles per hour, a re required to carry rockets past the point where the earth's gravitational pull . drags them back. Once that point is reached no fuel is needed unless specia l maneuvers or return of a manned vehicle is planned. The rocket coasts at ful l speed through space, no longer slowed down by at· mospheric friction. In early 1 959, such space probes were launched in or­ bit of the sun and by late fa l l a probe had landed on the moon and another had transmitted pictures of the moon's fa r side. Two a strona uts, Nei l Armstro n g and Edwin E . Aldrin, J r. , fi rst landed on the moon o n July 20, 1 96 9 (Ap o l l o 1 1 ) , while a third, Mike Col l i n s orbited the moon. Wearing space su its, they explored a s m a l l a rea n e a r t h e l a n d i n g c raft on foot. D u r i n g a l a n d i n g i n 1 97 1 (Apol l o 1 5 ) a batte ry- powered v e h i c l e w a s u s e d t o d rive a bout the l u n a r surfa ce , w h i c h a l lowed fo r more extensive exploration . On each l a n d i n g scien­ tific i n stru m e nts were l eft b e h i n d to record data, such a s s e i s m i c events, m a g n etism, variations i n tem pe rature, a n d othe r l u n a r c o n d itions, and to tra n s m it it back to earth. S a m p l es of l u n a r dust a n d roc k w e r e col­ l ected by th e astrona uts a n d retu rned to earth for scientific a n a lyses. Ma n n ed flig hts to Mars a n d Venus a re be i ng p l a n n e d .

PHASES OF THE MOON â&#x20AC;˘ On the earth we see the moon change from crescent to f u l l and back again in 2 9 Y2 days. If you were out in space, you would see that about half the moon is a lways l it up by the s u n and half is a lways i n darkness, except during a n eclipse. When the moon is m ost directly between us and the sun, we see only the dark side. But, beca use the moon is revolvi n g around the ea rth every 2 7 Ya days, varying a m ou nts of the lig hter side a re seen. When the earth is i n line between the sun a n d the m oon, we see the moon's fully i l l u m inated side a n d can watch it as a full moon from s unset to the next sun rise.

1 40



�it :;.'•:·<p�-:�02'.·

..:··· -. · ,

A l l other stages a re in between. When the moon is a q ua rter of the way around its orbit, we sti l l see h a lf its su rface, but half of this half is dark a n d ha lf is i l l u m i ­ n ated, g iving us a quarter m o o n . When t h e m o o n is more than a q ua rter, but less than full, it is cal led "gibbous." As the moon revolves a rou n d the ea rth, it rotates on its axis, keeping a l m ost the sa m e fa ce turned toward us. A slig ht wobble of the moon, d u e mainly to a s m a l l d if­ ference between the times of revol ution a n d rotatio n a n d t o a tilt o f the m o o n ' s a x i s , has a l lowed u s t o see from th e earth a tota l of 5 9 p e r cent of th e moon's sur­ fa ce. Luna r probes have now m a p ped the entire surfa c e . 141

EARTHSH I N E is l ight which has traveled from the sun to the earth, hence to the moon, a n d back a g a i n to the earth. Ea rth s h i n e i s very fa int because only a small part of the s u n l ig h t reflected from the earth h its the moon . The moon refl ects o n ly 7 per cent of this i nto space a g a i n a n d o n ly a t i n y fraction of this 7 per cent fin a l l y c o m e s back to earth. When y o u look f o r earthsh i ne, n ote that the crescent moon, because it i s b rig hter, seems l a rg e r.

1 42

LU NAR HALO â&#x20AC;˘ Rings around the sun a n d moon are often see n . These are in our atmosphere and are of the same genera l nature as rainbows. Ha los a re due to the refraction of s u n light or moo n l ight by thin, high, icy clouds. The halo making a 22-degree circle around the moon is the most common. A 46-degree circle may a lso form and, if the ice crysta ls in the clouds a re just right, one may see a rcs and other curious effects. Halos a re usua l ly colorless but sometimes they a ppear like faint rainbows with the red on the inside.

â&#x20AC;˘ The g ravitational p u l l of a p l a net, sate l l ite, or sta r decreases with d ista nce a n d with s m a l l e r weight or mass. The moon; though s m a l l, has a stron g g ravitati o n a l p u l l o n the earth because it is relatively v e r y n e a r. The s u n h a s a strong p u l l because of its g reat weig ht. This g ra vitatio n a l p u l l holds both the earth a n d the moon i n t h e i r orbits. The pul l s o f the s u n a n d the moon cause the tides, the moon having the g reater influence. The pull of the moon is greater on the side of the earth nea rest it, and is less on the opposite side of the earth, which is farther away. The difference betwee n the lesser and the stronger p u l l is eq u a l to a pu l l away from the moon. These pu l ls in opposite directions ca use the ocea n s to fl ow toward t h e axis o f t h e pu l ling. T h e result is a bulge of severa l feet or more i n the oceans on opposite sides of the earth. As the earth rotates and the moon revolves, th e b u lge of tides m oves a lso, g iving most places a lter n ating high and l ow tides. The tid a l pull of the more d ista n t sun is about ha lf that of the moon. When both p u l l in line at new a n d full m oon, the tides are higher. These are known


Spring Tide

Neap Tide

as spring tides. When they p u l l at rig ht a n g les and partly counteract one a n other, the tides are lower a n d are cal led neap tides. Tide schedu les ranging far i nto the future can be pre足 pared o n the basis of the m oon's predicted movements. The shapes of ocean basins and seacoasts may deter足 m i n e actua l heig hts of loca l tides. In genera l the tida l range is 3 to 1 0 feet. I n V-sha ped bays, as the Bay of F u n dy, the tide may rise 30 to 50 feet. I n broad bays it may rise a foot or less. 1 45

OBSERVIN G THE MOON • With the photograph and map on pages 1 46- 1 47 as a guide, you can easily study the moon and identify a dozen or two of the most promi­ nent features. Even a pair of small field glasses will show the "seas, " mountain ranges, and ringed plains, and the great "craters. " larger field glasses or a small telescope will disclose all the features identified on the map. The very best t i m e to observe the moon is in the two­ or three-day period after the first quarter. The moon is then in a good position for eve n i n g study; nea rly a l l m a j o r features c a n be s e e n a n d t h e m o o n i s n o t suffi­ ciently bright to cause loss of deta i l through g l a re . I t is even b ette r to fol l ow the moon eve n i n g after even i n g f r o m i t s first thin crescent t i l l it i s fu l l . As the l i n e of d a r k ­ ness recedes, features near the b o r d e r sta n d out i n bold rel i ef; the shadows become stronger a n d deta i l s a re m o re easily see n . S h o u l d you p a s s t h i s sta g e a n d desire t o explore the moon further, more detai led maps a re a va i l a b l e . These divide the fu l l moon u p into section s and s h ow you the features of each sectio n . Over 500 features o n t h e moon have been n a m ed . I ts whol e s u rfa ce has been m a pped. Detailed study will ca l l you r attention to inte resting p rob­ l e m s : t h e d istribution of craters; the overl a p p i n g of some craters; the nature of rays o n the moon; a n d the o r i g i n of the seas. Even thoug h the moon is o u r n e a rest neigh­ bor, there is m u c h we have yet to learn a bout it. How­ ever, s in c e we have visited the moon a n d b rou g h t back rocks f r o m i t, t h e n e w e r exploration wi l l prob­ a b l y be c h e m ical rath­ e r than a stro n o m i c a l . .

1 48

Total Eclipse of the Sun Showing Prominences and Outer Corona ECLIPSE OF THE SUN â&#x20AC;˘ Until recently n o astronomical event offered such o pportun ities as a tota l eclipse of the sun. Using new m ethods, astronomers can now m a ke some of the observations that once had to await a n eclipse. But "the bea uty and awesom eness of a tota l ec l i pse are sti l l uneq u a l e d . In the pattern of movements of moon, earth, and sun, there are a lways two to five solar ec l i pses each year. Some a re tota l , some parti a l , a n d some a n n u ­ l a r (p. 1 52). On t h e average there are two tota l eclipses of the sun every three years.

1 49

Tota l Eclipse of


SOLAR ECLIPSE • An ec li pse of the sun can occur only when the moon is new-when it is between the earth and the sun. If the orbits of earth and moon were on exactly the same plane and if these two bodies were at their mini­ mum distance apart, a n ec l ipse wou ld occur every month. It does not occur that often beca use the moon's orbit is incli ned about 5 degrees to the earth's orbit. I n ad dition, the moon's path takes it slig htly nea rer or fa rther from earth as it revolves. This is i m porta nt, a s the average length of the moon's sha dow is 232,000 m i les, but its dis­ ta nce from earth averages 235,000 m i les. A tota l ecli pse ca n n ot occur under average conditions. However, because of variations i n its orbit, the m oon's shadow is someti mes longer and its dista nce from ea rth someti m es shorter. If this occurs at the time of a new moon, we may have a n ecli pse. The tim e a n d p l ace of earth ecli pses a re calculated years in a dvance. At any one place the duration of tota l ity varies. i n the eclipse of

1 50

June 3 0 , 1 97 3 , the maxi mum tota l ity was a bout 7 m i n ­ utes, s l i g h lty less t h a n t h e o n e on June 2 2 , 1 95 5 . Y o u w i l l see a tota l eclipse w h e n t h e true s h a d ow ( u m bra) of t h e m o o n passes over you. The umbra pro­ d uses a roun d s h a d ow, never m ore than 1 70 m i l es i n d i a m eter, w h i c h travels ra pid l y over t h e earth. T h e pen ­ um bra, which surrounds the um bra l i k e a n i n verted c o n e , d o e s n o t c o m p l.etel y excl ude the sun l i g ht a n d hence g ives o n ly a partial eclipse. I t forms a circle a bout 4 , 0 0 0 m i l e s i n d i a m eter around the um bra . Observers i n the p a t h o f tota l ity s e e a parti a l e c l i p s e a s t h e d isc o f the m o o n cov­ ers m ore and m ore of the s u n ' s face. Then, at the m o ­ m e n t of tota l ity, r e d pro m i n ences a p p ear. The weird ly darkened s k y is lit up by the strea m i n g coro n a , w h i c h m a y exte n d over a m i l l io n m i l es fro m the sun ' s surfa ce . Noth­ i n g is a s i n sp iri n g a n d aweso m e a s the few m i nutes of tota l ity. Then, after repeati n g the partial pha se, the e c l i pse is over. 151

A N N U LAR EC LIPSE â&#x20AC;˘ The dista nce from the ea rth to the moon varies. If a n ec l i pse occurs when the moon is its average d ista nce away or farther, the u m b ra of the moon's sha dow does n ot reach the earth. An a n n u l us, or thin ring of sunlight, remains around the moon. The path of a n a n n u l a r eclipse is a bout 30 m i les wider than that of a tota l ec l i pse. Sur­ rounding this area, as in a tota l ec l i pse, is a region 4,000 to 6,000 m i les wide where the eclipse is parti a l . Of a l l sol a r ecli pses, a bout 35 per cent a re pa rti a l ; 32 per cent a n n u lar; 5 per cent both a n n u lar a n d tota l ; a n d 28 per cent tota l .

1 52

Right: Total Eclipses Visible in the Northern Hemisphere, 1 952-1 986

left, A n n u l a r E c l i p s e . Red Spot Shows Area in W h i c h A n n u l a r E c l i p s e I s S e e n ; E l sewhere i n the P e n u m b ra Eclipse


P a rt i a l

TOTA L E C L I P S E S O F SUN â&#x20AC;˘ The m ovements of s u n , m o o n , a n d e a rth c a u s i n g ecl ipses are w e l l k nown . They occur i n a cyc l e of j u st over 1 8 yea rs, after which a n ew series of ecli pses repeats with only m i n o r c h a n ges. O n e c h a n g e is a westward sh ift w i t h each n e w cyc l e . A k nowl­ edge of these cycles e n a b l e s a stro n o m e rs to predict eclipses h u n d re d s of yea rs i n advance. Ancienf e c l i pses are the m ost certa i n and useful of c h ronological data . T h e next tota l e c l i pse of the sun visible i n the U n ited States will ta k e p l a c e on Feb rua ry 26, 1 979 and w i l l be seen i n the Pa cific: Northwest. N ot until August 2 1 , 2 0 1 7 w i l l a n other tota l eclipse b e visi b l e fro m the U n ited States. A n n u l a r e c l i pses will be seen i n the U n ited States o n May 3 0 , 1 9 8 4 and May 1 0, 1 994. D u r i n g a sol a r ecli pse, tota l ity m a y last a s l o n g as seven m i n utes .

Total Eclipse of the Moon

LUNAR ECLI PSE â&#x20AC;˘ The earth's sha dow is some 900,000 miles long. When the moon enters into il a n d is ecl i psed, the ecli pse l asts a s long as sever a l hours and may be tota l for a s m uch as 1 hour and 40 m i n utes. In any year there may be no eclipses of the moon or as many as two and rarely three. Though there a re fewer ecli pses of the moon than of the sun, they last longer a n d ca n be seen by more people over a wider a rea. Because some of the sun light striking the earth is diffused a n d scattered by our atmosphere, the earth's shadow is not com pletely dark. Enough of this light reaches the moon to g ive it a faint coppery g l ow even when it is tota l l y ec lipsed. A n ecl i pse of t h e m o o n occurs o n l y a t t h e time o f ful l moon. Because of ang les of the moon's orbit, it may miss the TOTAL LUNAR ECLIPSES Date

J a n . 30, 1 972

May 25, 1 975 N ov . 1 8, 1 975 Sept. 6, 1 979 J u ly 6, 1 982 Dec. 30, 1 982 A p r i l 24, 1 986

1 54

T i m e af Midpoint of Ecli pse I E STI

5 :55 1 2 :45 5:25 5 :55 2 :30 6:25 7 :45

a.m. a.m. p.m. a.m. a.m. a.m. a.m.

D u ration of Eclipse

3 3 3 3 3 3 3

h . 25 m . h. 4 0 m . h . 25 m . h . 25 m . h. 45 m. h . 30 m . h . 30 m .

D u ration of Tota l i ty

0 1 0 0 1 1 1

h. 40 h . 30 h. 45 h . 50 h . 40 h. 5 h. 1 0

m. m. m. m. m. m. m.

shadow of the earth completely at that time, or it may only pass through the pen u mbra . A l u n a r eclipse offers proof of the earth's sha pe, for the umbra that passes over the moon has the distinct curve of a shadow of a ba l l . The ta ble shows tota l lunar ecli pses which c a n be seen in m ost parts of this country and southern Canada. 1 55

T H E C O N S T E L L AT I O N S T h e 88 g e n e ra l ly recog nized conste l l ation s a r e l isted b elow. A l l b u t a few a p p e a r on the sta r c h a rts i n this g u id e . Keep in m i n d that l atitude, season, e l evation, atmospheric c o n d itions, a n d time of n i g h t a l l determine whether a conste l lation is visi b l e. If a conste l l ation is too fa r south to be seen from a ny pa rt of the northern h e m i s p h e re, a fig u re is given wh ich is the n o rthern­ most l atitude at w h i c h the conste l l ation (or m ost of it) can be seen u nd e r good conditions. Thus the fig ure "25°N." fol lowing C rux mea n s that this constel l ation c a n be seen n o fa rth e r n orth tha n about 25°N. latitude-the latitude of southe rn F l o rida . The best season fo r seein g the conste l l ation is i n d icated by the date o n w h ich the conste l l ation reaches its h i g hest point a bove the h o rizon (the meridian) at 9 p .m. Each eve n i n g a c o n ste l lation reaches the meridia n about 4 m i n utes e ar l ie r than t h e previous eve n i n g ; each month, about 2 h o u rs earlier. Thus A n d romeda is o n the meridia n at 9 p.m. o n Nov. 1 0; at about 8:56 p . m . o n Nov. 1 1 ; at a b o u t 5 p . m . o n J a n . 1 0. Constel lation

On Meridian 9 p.m.


Nov. 1 0

Antlia (The Pump) 50°N.

Apr. S

Apus (The Bird of Paradise) S0N. Aquarius (The Water· bearer) 7S0 N . Aqu i l a (The Eagle)

J u n e 30 Oct. 1 0 Aug. 30


On Meridian 9 p.m.

C a n i s Minor (The L i t t l e Dog)

Mar. 1

Capricornus (The Goat, or the Sea Goat) 65° N .

Sept. 20

C a r i n a (The Kee l ) of the ship Argo, w h i c h i s n o l o n g e r a con· ste l l a t i o n . 2S0 N .

Mar. 1 S

Cassiopeia (The Quee n )

N ov. 2 0 M a y 20

Ara { T h e A l t a r ) 3 0 ° N .

J u l y 20

Aries (The Ram)

Dec. 1 0

Centaurus (The Cen· tour) 3 5 ° N .

Auriga (The C h a r i oteer)

J a n . 30

Cepheus (The King)

Oct. 1 S

Bootes {The Herdsman)

June 1 S

Cetus (The W h a l e )

N ov . 30

Coe l u m (The B u r i n ) 45° N .

Jan. 1 5

C h a m a e leon S0 N .

Apr. 1 S

Feb. 1

C i rcinus (The Com· passes) 25° N .

June 1S

C a m e l o p a rda l i s (The G iraffe) Cancer ( T h e C r a b )

Mar. 1 5

Canes Venatici {The H u nt i n g Dogs)

C o l u m b a (The Dove) 50°N .

May 20

Coma Berenices { Berenice's H a i r )

C a n i s Major (The Great Dog) 65° N .

Feb. 1 5

Corona Austrina (Southe r n Crown) 4S0 N .

1 56

J a n . 30 May 1 5 Aug. 1 5


On Meridian 9 p.m.


On Meridian 9 p.m.

Pavo (The P e a c o c k ) 20° N . A u g . 2S

C o r o n a Borea l i s ( N o r t h · e r n Crown)

J u n e 30

Corvus ( T h e Craw) 6S0 N .

May l O

Pegasus (The F l y i n g Horse)

Oct. 20

Crater (The C u p ) 70° N .

Apr. 2 S


Dec. 2 S

Crux (The Cross) 25°N.

May 1 0

C y g n u s ( T h e Swan )

Sept. 1 0

D e l p h i n u s (The D o l p h i n )

Sept. IS

Dorado (The G o l d fi s h ) 2S0 N .

J an . 2 0

Draco (The D r a g o n )

J u l y 20

E q u u l e u s (The C o l t )

P h o e n i x (The P h o e n i x ) 40° N .

Nov. 20

P i ctor (The E a s e l ) 30° N .

Jan. 20

P i sces ( T h e F i s h e s )

N ov. 1 0

P i s c e s Austr i n u s ( T h e S o u t h e r n F i s h ) SS0N .

Oct. 1 0

Sept. 2 0

P u p p i s (The Stern of t h e s h i p Argo)

Eridanus ( T h e River) 70° N .

Jan. S

Pyxis (The Compass) SS0N .

Fornax ( T h e F u r n a c e ) 5S0 N .

Dec. lS

Reticu l u m ( T h e N e t ) 2S0N.

Dec. 30

G e m i n i (The Twins)

Feb. 20

Sagitta (The Arrow)

Aug. 30

Grus (The C r a n e ) 3 S0 N .

Oct. 1 0

Hercu l e s

J u ly 2S

Sagittarius (The Arche r ) 60° N .

A u g . 20

Horologium (The C la c k ) 2So N .

D e c . 2S

Hydra (The Sea Serpent) 70°N .

Apr. 20

H y d r u s 1 S0 N .

Dec. 1 0

I ndus ( T h e I nd i a n ) 3S0N.

Sept. 2S

lacerta (The l i z a r d )

Oct. 1 0

lea ( T h e l i o n )

Apr. 1 0

Lea M i n o r (The l i t t l e lion)

Apr. 1 0

lepus (The H a r e ) 6S0 N .

J a n . 2S

libra ( T h e S c a l e s ) 70 • N .

J u ne 2 0

Scorp i u s (The Scar· p i o n ) ssoN .

Feb. 2S Mar. I S

July 20

Sculptor SS0 N .

Nov. 1 0

Scutum (The Sh i e l d ) 7S0 N .

Aug. I S

Serpens (The Serpent) 8S0N. Caput ( H e a d ) Cauda (Tai l ) Sextans (The Sextant) 8S0 N .

J u ne 30 Aug. S Apr. S

T a u r u s (The B u l l )

Jan. l S

Telescopium (The T e l e s c o p e ) 3S0N.

Aug. 2S

l u p u s ( T h e W o l f ) 4S0 N .

J u ne 2 0

T r i a ng u l u m ( T h e Tria n g l e )

Dec. S

Lynx (The l y n x )

Mar. S

Lyra (The lyre)

Aug. I S

T r i a ng u l u m Austra l e ( T h e Southern T r i a n g l e ) 20° N . Tucana (The Toucan) 20°N.

N o v. S

Mensa (The T a b l e Mounta i n ) S0N . Microscop i u m ( T h e Microscope) S0° N .

Jan. 30

July S

Sept. 2 0

U rsa Major (The G r e a t Bear)

A p r. 2 0

Monoceros (The U n i c o r n ) 8 S0N .

Feb. 20

U rsa M i n o r (The l i tt l e Bear)

Musca (The Fly) 1 S0 N .

June 2S

May l O

V e l a (The S a i l s o f t h e s h i p Argo) 3 S0 N .

Mar. 2 5

N o r m a ( T h e leve l ) 3 S 0 N .

July S

Octans (The Octan t ) S0 N .

Sept. 20

Ophiuchus (The Serpent Bearer) 8 S0 N . Orion 8S0N.

V i rg o (The V i rg i n ) 80°N .

M a y 2S

J u l y 25

Volons (The F l y i n g F i s h ) 1 S0 N .

Mar. !

Jan. 25

V u l pe c u l a ( T h e F o x )

Sept. 1 0

1 57


(Middle North Latitudes) Positions given in as­ tronomical periodicals. Large as­ teroids, when near earth, can be spotted with binoculars. Planets: See pp. 1 24 - 1 25. Use bin· oculars for 4 of Jupiter's moons and Venus' crescent; telescope for Saturn's rings. Positions of Uranus and Neptune given in astronomi� cal periodicals. Meteors : Table of showers, p. 1 30. Suggestions, pp. 1 29- 1 33 . Mizar (star): In Big Dipper, p. 64. Note companion, Alcor.




.. ...



Constellations: See seasonal charts, pp. 54-99. Learn first those with brighter stars. Bright Stars: See list, p. 35, and seasonal charts. Identify star types by color (p. 37). Estimate magni­ tudes by comparison. The Moon: Detailed suggestions on p. 1 48. Map, pp. 1 46- 1 47. o r e ���.r ar'::.rlk in!!� ��:� �ho� :;�d� of stars. Note dark nebulae be· tween Cygnus and Scorpius, and star fields in Cygnus and Sagittarius.


; ;:: ..



u c z c

V I S I BLE D U R I N G PART OF T H E YEA R (Middle North Latitudes) The celestial objects listed below are at the meridian at 9 p.m. standard time during the months indicated. They are visible in middle latitudes for one or more months before and after the months indicated. Their positions when observed depend on your latitude and the hour of observation. Ja n u a ry Binoculars show glowing cloud; tel· escope, individual stars. Pleiades (open cluster) : Near Per­ M6 and M7 (open . clusters): In seus, pp. 82 and 86. Scorpius (pp. 72 , 76) , 5° northeast Hyades (open cluster) : In Taurus, pp. 90-91 , 93 . Easy for naked eye. of tip of tail. fine in binoculars. August M42 (Great Nebula) : In Orion, pp. Epsilon Lyrae (double star): I n 90, 92. I mpressive in binoculars. lyra, 2° n o rtheast o f Vega, pp. Betelgeuse (variable red giant): 72, 75 . C l ose pair. In Orion, pp. 9 0 , 92. Compare each is a double. Telescope shows with Rigel (mag. 0.3, p. 92) and September Procyon (mag. 0.5, p. 95). Albireo (double star): In Cygnus, February p. 78 . Small telescope reveals pe�ir, M35 (open cluster): In Gemini, orange and blue. Superb. near Castor's left fool, pp. 65, 66. November M31 (Great Spiral Nebula in An· M a rc h dromeda) : See p. 85. Small, faint M44 (open cluster) : In Cancer, in o eye; glowing center of ''square/' p. 6 4 . Called or Beehive. Splendid in �r0 �d {� bi���1:�s. �i��:�ra"rs. D ece mber Double cluster In Perseus: In cen· May ter of Perseus, p. 82. faint, hazy Coma Berenices (open cluster): becomes, in binoculars, a Between Leo and Bootes, pp. 64-65. patch splendid spray of stars. Use binoculars. Algol (eclipsing variable): In Per­ July seus, p. 86. Observe magnitude M13 (globular cluster): In Hercu· changes. Compare with Polaris les, pp. 72, 74. Faint, fuzzy spot. (mag. 2.1 ) .

1 58

I NDEX Bold type

denotes pages containing more extensive i nformation.

. Achernar, 35 Albireo, 78 \ ldebaran, 35, 37, 9l ·Ajgol, 38, 39, 86 Alpha Draconis, 53 , 58 A l phard, 63 A l pheratz, 84, 85 Altair, 35, 7 1 , 79 Amateur activities, 7- 1 0 Andromeda (an-DROM· e·duh), 80-82, 85 Antares (an-TA I R -eez) , 32, 33, 35, 37, 70, 76 Aquarius, the Water Carrier, 82, 1 00 Aquila ( u h - KW I L- u h ) , t h e Eagle, 7 2 , 7 9 Archer, 7 2 , 77, 1 00 Arcturus, 3 5 , 3 7 , 6 1 , 68 Aries (AI R-eez), the Ram, 8 1 , 1 00 Arrow, 7 1 , 79 Asteroids, 1 02, 1 2 3 Astronomy, 4 , 50 , 1 01 Atmosphere, earth 's, 20-2 1 , 24-27, 1 1 0 Auriga (oh -RY-gu h ) , t h e Charioteer, 8 7 , 90 Aurora, 23, 24-25

\ if.

Betelgeuse (BET-el­ gerz ) , 34, 35, 37, 7 1 , 89, 92 Big and Little Dogs, 90, 95 Big D ipper, 51 , 54, 56 Be>Otes (boh -OH-teez) , the Herdsman, 64, 68 B u l l, 33, 40-41 , 88, 9 3 , 94, 1 00 Cancer, the Crab, 62, 65, 1 00; c luster, 40 Canis ( KAY-n is) Major and Minor, 90, 95 Canopus, 35, 37, 99 Capella, 35, 37, 38, 87 Capricornus, 83, 1 00 Cassiopeia (kas-i-ohPEE-uh), 55, 59, 6 1 , 80 Castor, 34, 38, 6 1 , 66 Centaur (SEN -tawr), 97, 98 Cepheid (SE E-lid ), 34, 3 9 , 51, 60 Cepheus (SEE-fuhs) , the King, 55, 59, 60, 80-8 1 c ••••• 1 5, 1 23

Cetus (SEE-tuhs), the Whale, 39, 8 1 , 82 C harioteer, 87, 90 C l u sters, 40.41 , 62-63, 66, 74, 76, 77, 87, 94 Coal sacks, 45 Co lors, 1 8 - 1 9, 26-27 Columba, the Dove, 89, 96 Coma Berenices (ber­ ee-NY-seez), 40, 63, 64, 73 Comets, 1 02 , 1 26- 1 28 Conste l lations, 50·1 01 ; autumn, 80-87; key to, 61 ; l i st, 1 56- 1 51; north circumpolar, 5261 ; south circumpolar, 97-99; spring, 6269; summer, 70-79; w inter, 88-96; zodiac, 1 00 - 1 01 Corona Borea lis (boh­ ree-AL-is), North­ ern Crown, 70, 72-73 Corvus (KOH R-vuh s) , the Crow, 63, 73 Cosmic dust, .C2 Counterglow, 1 35 Crab, 62, 65, 90, 1 00 Crater, the C up, 64 Crow, 63, 73 Crown, 70, 72-73 Crux (CRUHKS), 45, 99 Cup, 64 Cygnus ( S I G -nuhs) , the Swan, -45, 46, 71 , 72, 74, 78 Day and n ight, 1 1 2-1 1 3 Decl ination, 7 1 Degrees, measuring by, 71 Delphinus (de i - FY­ n u h s ) , the Dolphin, 7 1 , 72, 79 Demon Star, 86 Deneb, 35, 46, 7 1 , 78 Denebolo, 67, 69, 7 1 Dolphin, 71 , 7 2 , 79 Dove, 89, 96 Draco ( DRAY-koh), the Dragon, 55, 58 Eagle, 72 , 79 Earth, 53, 1 04, 1 1 D- 1 1 5 Earthshine, 1 42 E c l i pses, 1 49 - 1 55 Ecliptic, 1 00

Fishes, 8 1 , 82, 1 00 Fomalhaut (FOHm al - o ) , 35, 81 Fraun h ofer li nes, 1 8- 1 9 Ga laxy, 42-45 G a l i leo, 28 Gegenschein, 1 3 5 Gemi n i (JEM-i-nee), the Twins, 6 1 , 65, 66, 1 00 Goat, 83, 87, 1 00 Great Bear, 40, -46, 5 1 , 52, 54 , 56 Hare, 89, 96 Herc u l es, 33, 70, 74 ; cluster, 4D-4 1 , 74 Herdsman, 6 1 , 68 Horse, Wi nged, 80-8 1 , 84 Horse-head Nebula, 45 H unter, 92 Hyades ( HY-uh-deez), 93-94 Hydra, the Sea Mon­ ster, 63, 73, 90, 98 Job's Coffin, 71 , 79 J upiter, 1 0, 35, 1 02, 1 05, 1 1 8- 1 1 9, 1 25 King, 55, 59, 60, 80-81 Kuiper, G. P., 1 06 lapl.ace h ypothesis, 1 06 Leo, the Lion, 61 , 62, 67, 1 01 Lepus ( L E E -pus), the Hare, 89, 96 Libra ( LY-bruh ) , the Sca les, 70, 73, 1 00 Light year, 3 1 Lion, 61 , 62, 67, 1 0 1 Little Bear, 54 , 57 Little Dipper, 54, 57 Little Dog, 95 Lyra (L Y -ruh ) , Lyre, 72, 75 Mage l l anic C l ouds, 43, 97, 98 Magnitudes, 34-35, 51 Mars, 32, 35, 1 02, 1 041 05, 1 1 6- 1 1 7, 1 24 Mercury, 35, 1 02, 1 041 05, 1 08 Messier, Charles, .Cl Meteors and meteorites, 1 0, 67, 1 02, 1 26- 1 27, 1 29 - 1 33; observing, 1 0, 1 32; showers, 1 30

1 59


Midnight sun, 1 1 4-1 1 5 M i l k D i pper, 7 1 , 77 M i l k y Way, 40-45, 7778 M i r a (MY- r u h ) . 39, 81 M i z a r (MY-za h r ) , 34, 3 8 , 56 Moon, 1 3 , 1 02 , 1 3 6· 1 48 ; e c l i pse, 1 54 1 55; map, 1 46- 1 47; see also planets


"' u ! z ... .. �

0 �

;!: 2 ! w

� �

.. z

... •

� :! :I

N e b u l a e ( N E B - u - lee ) , 4 1 , 42, 43 , 4 5-47, 58, 75, 77, 8 1 , 85, 92 Nebular h y poth e s i s , 1 06 Neptune, 1 04- 1 05, 1 22 Northern C ross, 45, 7 1 , 72, 74, 7 8 , 83 Northern C r o w n , 64, 70, 73 Northern l i g h t s , 23 -25 N orth Star, 34, 39, 50, 53, 56- 5 7 . 58, 60, 6 1 Novae, 39, 46, 59 Observatories, 8, 28, 30 Observ i n g , 5-7, 8 8 , 1 32 , 1 48 , 1 58 Oph i uc h u s ( a h f- i - U k u h s ) . t h e Serpentbearer, 70, 72 Orion ( o h - RY -ah n ) , t h e H u nter, 77, 8 8 , 92 : n e b u l a , 45, 47, 92 Pegasus ( P EG - u h -suh s ) , t h e W i n g ed H orse, 80-8 1 , 84 Perseus ( P E R - s u s ) , 38, 40, 59, 80-8 1 ' 8 6 Photography 1 0, 2 9 , 89 Pisces ( P I S - e e z ) , the F i s h e s , 8 1 , 82 , 9 1 , 1 00 P l a neta r i u m s , 8 P l a n ets, 1 2 - 1 3 , 1 021 22 , 1 23 ; b r i g h t ness, 34-35; t a b l e , 1 04 - 1 05; l ife o n , 1 03 ; locating, 1 24 P le i a d e s ( P l E E - y u h d e e z ) , 4 1 , 88, 94 P l u to, 1 02 , 1 05, 1 22 Polaris ( p o - L A - r i s ) . 34, 5 0 , 5 3 , 56-57. 58 , 60, 61 P o l l u x , 35, 6 1 , 6 6 Prece s s i o n , 5 3 , 60 Procyon ( P RO-see-y u n ) , 35, 37, 95 Pyramids, 4

1 60

Q u e e n , 55, 5 9 , 6 1 , 80 Radio astronomy, 29, 47 Rainbow, 20-21 R a m , 8 1 , 1 00 Re u l u s ( R E G - y oo- l u h s ) . 5, 6 1 , 67 R i g e l , ( R Y- j e l ) , 3 5 , 3 7 , 71, 89, 92 Right asce n s i o n , 7 1 R i n g N e b u l a , 47 Rocket t o moon, 1 38

S a g i tta (suh-J I T - uh ) , the Arrow, 7 1 , 79 Sagittarius ( s a j - i - TA I R ee-uhs) . t h e Archer, 42, 7 1 , 72, 7 7 , 1 00 Sate l l i tes, 1 02 ; see also u nder planet names Saturn, 35, 1 02 , 1 2 0· 1 2 1 , 1 25 Sca,les, 70, 73 , 1 00 Scorpius, the Scorpion, 45, 70, 76, 77, 1 0 1 Sea Monster, 63, 73 , 98 Seasons, 1 1 4- 1 1 5 Serpens, t h e Serpent, 70-7 1 ' 83 Serpent-bearer, 70, 72 Seven S i sters, 4 1 , 88, 94 S h o o t i n g stars-see Meteors S i c k l e , the, 67 Sirius (SE E-ree-us), 3 1 , 33, 35, 36, 89 S k y , color of, 26-27 Solar system, 1 4- 1 5, 1 02- 1 5 5 ; components, 1 02 - 1 03 ; in g a l a x y , 42; movement, 33, 74; o r i g i n , I 06- 1 07 Southern Cross, 46, 53 , 63, 97, 99 Spectrum, 1 8· 2 1 , 3637, 48-49 Spica (SPY -ku h ) , 3 5 , 36, 38, 69 Stars, 3 1 -49; brigh test, 3 5 ; brigh tness, 3 2 , 34- 3 5 , 3 8 -39, 4849, 5 1 ; c l a ssifical i o n , 36-39; c l u s ters, 40·4 1 , 62-63; 7 4 , 8 7 ; colors, 3 3 ; density, 33, 76; distances, 3 1 ; d o u b l e a n d t r i p l e, 3 5 , 3 8 39; eclipsing, 38; energy, 3 2 ; g i a n t s

Stars (con f . ) : and d w a rfs, 1 4 - 1 5, 3 3 , 48-49, 92 ; l ight, 3 2 ; m a g n itudes, 34 -35, 5 1 ; motions, 33; n a m e s , 5 1 , 89; n u m be r s , 3 1 ; o r i g i n , 48-49; s i z e , 32; spectra, 3 6 -37; temperatures, 1 6, 2 2 , 3 2 , 3 6 - 3 7 . 45; v a r i a b le, 1 0, 34, 39 , 60 S u n , 1 6- 2 7 : b r i g h t n e s s , 3 2 ; c l a ssification, 3 7 ; d i stance, 3 1 ; e c l i pses, 1 49- 1 53 ; light, 1 8- 1 9 , 2627, 1 1 4- 1 1 5; observ i n g , 1 6 ; spots, 2 2 - 2 3 , 25; tide, 1 1 4- 1 45 Sund i a l , 5 S u n r i se a n d s u n set, 26 Swan, 7 1 , 72, 74, 78 T a u r u s (TAW R - u s ) , t h e B u l l , 3 3 , 88, 9 3 , 94, 1 00 ; c l u sters, 40- 4 1 T e l e scopes, 1 0, 2 8· 3 0 ; making, 9 Thuban-see A l p h a Draco n i s T i d e s , 1 44- 1 45 Time, 1 1 2 - 1 1 5 Tria n g u l u m , the T r i a n g le, 8 1 , 85, 98 T r i fi d N e b u l a , 46 Twi l i g h t , 27 Twins, 6 1 , 65, 6 6 , I 00 U n iverse, t h e , 1 2 - 1 3 Uranus ( U -ruh-nuhs), 34, 1 04 - 1 05, 1 22 U rsa ( E R - s u h ) Major, the B i g Bear, 40, 46, 5 1 ' 52 , 54, 56 U r s a ( E R - s u h ) Minor, t h e l i t t l e Bear, 54, 5 7 V e g a ( V E E - g u h ) . 35, 37, 53 , 7 1 , 75 V e n u s , 34, 35, 1 02 , 1 04-1 05, 1 09 , 1 24 V i rg o ( V E R -g o h ) . the V i r g i n , 63 , 6 4 , 6 9 , 1 00 W a t e r C a r r i e r, 8 2 , 1 00 W h a l e , 39, 8 1 , 82 Zodiac, 1 00- 1 0 1 Zod i a c a I I i g h t , 1 34- 1 3 5




HER B E RT S. ZIM, P h . D . , S c . D . , an o r i g i n a t o r a n d for­

mer ed i t o r of the G o l d e n G u i d e S e r i es, was a l so an a u t h o r fo r many years. A u t h o r of some n i n ety books and ed i t o r of about as m a ny, h e is now Adj u n ct Pro­ fessor at the U n i ve r s i ty of M i a m i a n d E d u c at i o n a l Co n s u l ta n t to t h e A m e r i c a n F r i e n d s S e rv i c e Co m m it­ tee and o t h e r o rgan izat i o n s . H e works o n e d u ca­ t i o n a l , p o p u l at i o n and e n v i ro n m e n t a l p r o b l e m s . ROBERT H . BAKER, P h . D . , D . S c . , now d eceased, was

fo r m e r l y head of the U n ivers i ty of I l l i n o i s Depart­ m e n t of A s t r o n o m y . H e was the a u t h o r of t h e stan­ d a rd co l l ege text A s tron o m y, o n e of t h e m o s t w i d e l y u sed i n t h e U .S . A . H e a l s o wrote An Introduction to As tron o m y a n d Wh en the Sta rs Come Out. JAMES GORDON IRVING has exh i b i ted p a i n t i ngs at

t h e A m e r i c a n M u s e u m of N a t u ra l

H i st o ry a n d t h e

N a t i o n a l A u d u bo n Soci ety. I n t h e G o l d e n G u i d e S e r i e s h e h a s i l l u strated Mammals, B irds, Insects, Rep­ tiles a n d A m p h ibians, Sta rs, Fishes, and G a m e b irds .



77303961 stars a golden guide  


77303961 stars a golden guide