Stars - A Golden Guide

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GOLDEN GUIDES NATURE BIRDS

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BUTTERFLIES AND MOTHS

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CACTI

EXOTIC PLANTS FOR HOUSE AND GARDEN FLOWERS

FOSSILS

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HERBS AND SPICES

GAMEBIRDS •

REPTILES AND AMPHIBIANS THE ROCKY MOUNTAINS

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TROPICAL FISH

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CATS

FISHES

INSECTS •

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MAMMALS

POND LIFE

ROCKS AND MINERALS

SEASHELLS OF THE WORLD

SKY OBSERVER'S GUIDE TREES

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ORCHIDS

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HALLUCINOGENIC PLANTS

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INSECT PESTS

NON-FLOWERING PLANTS

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•

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SPIDERS AND THEIR KIN

WEEDS

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YOSEMITE

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SEASHORES STARS

ZOO ANIMALS

SCIENCE BOTANY

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GEOLOGY

ECOLOGY •

HEART

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EVOLUTION

LANDFORMS

OCEANOGRAPHY

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•

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FAMILIES OF BIRDS

LIGHT AND COLOR

WEATHER

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ZOOLOGY

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ANTIQUES

HOBBIES AMERICAN ANTIQUE GLASS CASINO GAMES INDIAN ARTS

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FISHING

KITES

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WINES

GOLDEN FIELD GUIDES AMPHIBIANS OF NORTH AMERICA BIRDS OF NORTH AMERICA

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ROCKS AND MINERALS

SEASHELLS OF NORTH AMERICA

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TREES OF NORTH AMERICA

G olden ®, A Golden Guide®, and Golden Press® are trademarks of Western Publishing Company, Inc.

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A GUIDE TO THE CONSTELLATIONS, SUN, MOON, PLANETS, AND OTHER FEATURES OF THE HEAVENS

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

Illustrated by JAMES GO RDON I RVING

�

GOLDEN PRES S

•

NEW YORK

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

FOREWORD

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

4

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

7

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

STARS .

36

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

··················

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

Galax i e s...

50

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

52

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

62

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

70

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

88

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

98

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

.

.......................129

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

..........................................126

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

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

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

.....158

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

3

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.

4

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.

A C T I V I T I E S FO R T H E AMATEUR

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.

FOLLOWING THE P LAN ETS

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

7

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.

T E LESC OP E MAKING

9

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.

10

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.

02138.

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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

12

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 ­ 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 .

14

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.

16

....

. .

Sunspots

Photosphere

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

G

F

E

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 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.

D

c

B

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

20

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

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 ­ 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 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° 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

24

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 acter. A few days after' a large new sunspot group de­ velops, an auroral display is likely to occur.

25

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 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 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 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 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 escopes are reflectors (see page 30). Reflec­ 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 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 ­ 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 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 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.

32

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).

34

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

Distance

(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 - 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

9.

I N ASA)

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 · 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 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

and

Six

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 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 l ieved to have an atmosphere. 121

Photographic Plates by Which

URAN US, NEPTU NE, and PLUTO • 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 • 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

LOCAT I N G T H E V I S I B LE P LA N E T S

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 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 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

L.

W h i p ple)

J A N U ARY

APRIL

J U LY

OC TOBE R

VENUS

1 975

C a p r i corn us

Taurus

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

Op hiuch us A q u a r i us

Pisces Aries

Scorpius

Aquarius

C a p r i corn us

Tau rus

lea

Lea Li bra

Taurus Leo

Virgo l i b ra

Tau rus

Leo

Path of Saturn

1 970- 1 9 8 5

Venus in Leo, J uly 1 978 1 975

Sagittarius

1 976

Tau r u s

1 977 1 978

Sagittarius

1 979 1 980

Cancer Leo

Mars in Gemini, April 1 976 MARS Aquarius

Aries

Taurus

Gem i n i

leo

V i rgo

Aquarius

Taurus

Gemini

leo

l i bra

Pisces

Taurus

Cancer

leo

V i rgo

Scorpius

Ca n ce r

J U PITER

1 975 1 976

A q ua r i us P i s ces

Pisces

Pisces

Taurus

Taurus

1 977 1 978 1 979

Aries

Tau rus

Taurus

Gemini

Taurus

Gem i n i

Gemini

Cancer

Cancer

Cancer

Ca n ce r

Leo

1 980

Leo

leo

leo

Virgo

1 975

Gemi ni

Gem i n i

1 976

Cancer

Gemi ni

1 977 1 978 1 979 1 980

Cancer

Ca n c e r

C a n cer

Leo

Leo Leo

leo Leo

leo L eo

Leo Leo

Virgo

leo

Virgo

Virgo

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 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 oids . The head of a comet may consist of ice a n d m eteoric p a r­ 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 ­ 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 creases. Most comets lack a s pectac ular tai l ; i n others it develops rapidly a n d may be­ 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

SOM E FA

M.qU S

C O M ETS

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 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 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

IMPORTANT AN NUAL METEOR SHOWERS Date

Shower

Jan. 2-3

Q u a d r a n tids

Location of Radiant E

Between Bootes a n

d

heod of Draco NE

Between Vega a n d Hercules

Apr. 20-22

lyrids

May 4-6

Aquarids

Aug. 1 0- 1 3

Perseids

Oct. 8 - 1 0 -

D raco n i d s

E

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

Oct. 1 8 -23

Orionids

E

Between Orion a n d Gem i n i

Nov. 8-1 0

Taurids

Dec. 1 0- 1 2

G e m i n ids

E

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

NE

Pe

rse u s Period a b o u t

NE

61h

years

Between Ta u r u s, Auriga, and Perseus

E

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 night. An observer can usua l ly see about 10 per hour. Occasionally g reat m eteor showers fill the sky with celes­ tia l fi reworks. These are rare, but lesser showers of me­ 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.

H O W TO O B S E R V E M ET E O R S

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.

METEOR CH ART

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 ing light is best observed in the ea rly evenings of March a n d April and just before dawn in September and Octo­ 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 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 • 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 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 • 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

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�it :;.'•:·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

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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

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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

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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

U U VV WW X X

STARS A GOLDEN GUIDE

®

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 .

GOLDEN PR ESS

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NEW YORK