Sky Observers Guide - Golden Guide.pdf

A GOLDEN GUIDER

Complete your collection of Golden Guides and Golden Field Guides! GOLDEN GUIDES BIRD LIFE

BIRDS

•

DINOSAURS FISHING

•

•

BUTTERFLIES AND MOTHS

•

EXPLORING SPACE

FLOWERS

INDIAN ARTS

•

FOSSILS

INSECTS

•

PLANETS

•

•

•

•

FISHES

GEOLOGY

MAMMALS

POND LIFE

REPTILES AND AMPHIBIANS ROCKS AND MINERALS SEASHELLS OF THE WORLD SEASHORES

•

SKY OBSERVER'S GUIDE

SPIDERS AND THEIR KIN TROPICAL FISH

•

•

STARS

•

TREES

VENOMOUS ANIMALS

WEATHER

•

WEEDS

WHALES AND OTHER MARINE MAMMALS

GOLDEN FIELD GUIDES BIRDS OF NORTH AMERICA REPTILES OF NORTH AMERICA ROCKS AND MINERALS SEASHELLS OF NORTH AMERICA SKYGUIDE TREES OF NORTH AMERICA WILDFLOWERS OF NORTH AMERICA Golden®, A Golden Guide®, and Golden Press"

are trademarks of Western Publishing Company, Inc.

THE

SKY OBSERVER'S GUIDE

A HANDBOOK FOR AMATEUR AS TRONOMERS

by R. NEWTON MAYALL, MARGARE T MAYALL and JEROME WYCKOFF Paintings and Diagrams by JOHN POLGREEN

� •

GOLDEN PRESS • NEW YORK Western Publishing Company, Inc. Racine, Wisconsin

Special Acknowledgment The maps on pages 148-157 were designed by R. Newton Mayall

© 1985, 1977, 1971, 1965, 1959 by 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. Published by Golden Press, New York, N.Y. library of Congress Catalog Card Numbe" 65-15201. ISBN 0-30724009-6

Solar Prominences compared to Size of Eorth

Contents Becoming a Sky Observer 5 The Observer's Equipment 10

,

Understanding the Sky 21 First Steps in Observing 29 Using a Telescope 35 Star Charts and Setting Circles 45

55 The Sun 66 Sky Colors 74 The Planets and Asteroids 78 Comets 94 Meteors 98 Stars 102 Nebulas 117 Drawing Sky Obj ects 122 The Sky Observer's Camera 125 Using Astronomical Time 135 Accessories and Maintenance 138 lncidentallnformation 146 Maps of the Heavens 148 Index 158

8 SUN

�

VENUS

Q

MERCURY

EB

EARTH

The Moon

))

MOON

�

JUPITER

0

6

MARS

F-t

SATURN

URANUS

E

PlUTO

t_p NEPTUNE

Ring Nebula (MI. Wilson)

Some FAVORITE SKY OBJECTS For OBSERVATION

Becoming a Sky Observer All of us, from childhood, have gazed at the sky i n wonder. Sun a n d Moon, t h e wanderi n g planets, the fiery trails of comets and meteors-these a re things to marvel at. Man will never tire of looking u p into the tremendous, sparkling bowl of space. Skywatching was undoubtedly a pastim e of pre­ historic m a n . The ancient Egyptians and Babylonia ns, severa l thousand years ago, observed the h eavens care­ fully enough to devise q uite accurate calendars. Ob­ servations by Copernicus, Gali leo, and others in the sixteenth a n d seventeenth centuries were among the first great steps to modern science. Even today, the science of astronomy depends on observation. Astronomy is for the amateur as wel l as the professional. The amateur can see for himself the sig hts that sti rred Ga li leo, the Herschels, and other great astronomers. A high-school boy may be the first to see a comet, a rug sa lesman may discover a nova, and a housewife can observe and map meteor showers. An amateur's faithfu l observations of a variable sta r may be just the data an observatory needs. Although in some re­ gions weather and climate ASTRO N OMY FOR EVERYBODY

Mars-o challen ge to astrono­ mers: T h i s p h oto of the red p l a n ­ et, a lways a favorite of o bse rvers, is one of the fin est. (W. S. Finten, Union Obs., Johannesburg)

Great Nebula in Orion:. This famous object was p a i n ted as seen by the artist in h i s 8-inch telescope at 200 power. The pattern of four stars near the center is the well-known, col o rfu l Trapezi u m .

are often unfavora ble, any interested person i n any part of the world can become a sky observer. The aspect of the sky differs from place to p lace, but the majesty of Sun a n d Moon, of sta rs and planets a n d nebu las, is to be seen everywhere. This book is a g uide to observing-to the use of binoculars and telescopes, the locati ng of sky objects, and what objects to look for and how best to see them. The beginning observer should have also a book on genera l astronomy. Even a little knowledge greatly increases the pleasure of observi ng, a n d it prepa res us to undertake rea l astronomica l projects. Most old hands have found that the fun of amateur astronomy is greatest when they a re working on observation programs that are scientifica l ly usefu l. Even a n observer without binocu lars or a telescope ca n see many wonders of the heavens. The importa nt th ing is to know how to

O BSERV I N G WITH UNAIDED EYES

6

look and what to look for. The constel lations ca n be traced and identified. Some star clusters can be located, and eclipses and some comets observed . The changing positions of Sun, Moon, and the brighter planets can be closely watched, and some a rtificia l satel lites can be seen. The brightness and length of meteor trails can be estimated. Get used to finding your way a bout the sky with the eyes a lone before tryi ng a telescope. Your fi rst look at the heavens through good binoculars can be exciting. Binoc­ u lars with 50m m . lenses gather a bout 40 times as m uch light as the eye a lone, revea ling such features as mountains a n d craters of the Moon, sunspots, the four larger satellites of J upiter, double stars and star clusters, and luminous clouds of cosmic gas such as the famous nebula i n Orion . (Before observing Sun, see pages 66-67!) With no more than binoculars, some observers do useful scientific work, such as recording light changes i n variable stars and watching for novas and comets. A telescope is ob­ tained by every serious amateur sooner o r later. Refractors, with lenses 1% to 4 i n ches diameter, a n d reflectors, with mirrors of 3 to 6 inches, are popular types. The light-gathering B I N OCULARS A N D TELESCOPE

Telescope on wheels: T h i s home· mode 8-i nch reflector is kept i n the g a rage a n d wheeled o u t at observing time. (William Miller)

and mag nifying power of telescopes brings out details of the Moon's surfa ce. It reveals J upiter's larger satellites and its ba nded clouds, as we ll as ma rkings on Mars a n d the rings of Saturn. With telescopes we can "split" double sta rs and disting uish sta r clusters, nebu las, com­ ets, and sunspots. We ca n watch the Moon occult (that is, pass in front of) sta rs and p lanets. light fluctuations of faint va riable stars and novas can be detected. Good sma l l telescopes can give surprising per­ forma n ce. When conditions are right, a n observer with a good 3-inch refractor or 6-inch refl ector ca n see some featu res of J upiter and Saturn more distin ctly tha n they a ppear in observatory photographs. FUN W I T H T H E CAMERA Many a mateurs make use of the camera . The eye is sensitive o n ly to the light it is receiving in the present insta nt, but photog ra phic fi l m i s sensitive t o light received over a l o n g period o f ex­ posure. An amateur's camera ca n detect faint objects which the eye, even with the aid of a telescope, could never see. Even a simple camera gives exciting and useful results. MAKI N G

A

TELESCOP E

Some serious amateu rs, not content with factory­ made telescopes, make their own . They g rind the Transit of Mercury, Nov. 1 4, 1 907: The move m e nt of a pla net a cross the S u n 's disk i s a rare sight. Arrows poi n t to Merc u ry a nd show the d i recti o n of its path . (Yerkes Obs.)

For a serious a mateur: This homemade 1 2-inch reflector, e q u i p ped with a camera, can g ive h i g h perfo r m a n ce . (Clarence P. Custer, M.D.)

lenses a n d m irrors, and design the mou ntings. It takes specia l knowledge and skill, yet hundreds of amateurs have made instruments that perform splendid ly. Tele­ scope-making classes a re held at some planeta riums, universities, a n d observatories. Books on telescope making a re availa ble from booksel lers. Ma ny a mateur ob­ servers belong to nationa l organizations. These give mem bers info rmation on equipment, observi ng tech­ niq ues, and sta ndard methods of reportin g thei r work. They set up observing progra ms and receive obser­ vational data from mem bers. Data a re sent to ob­ servatories for use i n programs of research. Some organizations publish news of developments that interest a mateurs. loca l g roups observe together, compare equipment, a n d promote pu blic interest i n astronomy.

ORGA N IZAT I O N S OF AMATEURS

9

Three types of telescope: The reflector, with a mirro r for its objective, i s a common a l l-purpose desi g n . The refractor, using a lens for the objective, also is a n a l l-pu rpose type. The tracking telescope has the extra-wide fiel d needed for fast-movi ng objects.

The O bserver's Equipment J ust as we gather a supply of maps and booklets before touring the country, so we m ust gather certain sources of information before touring the sky. This book provides all necessary i nformation for a good sta rt in sky observi ng. The index wi l l g uide you to exp lanations of observing techniques and equipment, to lists of i nteresti ng objects to look for, and to tables indicating where and when to look for planets, eclipses, meteor showers, and periodic comets. For more back­ ground in astronomy, the reader may turn to books a nd periodicals recommended on pages 1 46- 1 47. Hundreds of stars, nebulas, and other objects ca n be located with the aid of the maps on pages 1 48- 1 57. For fainter objects the more detai led cha rts to be found

C H A RTS AND BOOKS

10

in a star atlas become indispensa ble. There a re atlases of convenient size that show nea rly a l l stars as faint as can be seen with binocu lars. For serious work with a telescope, more detai led charts a re needed. Some begin ners use a planisphere to learn constel­ lations. One type has a "wheel" on which is printed a map of the constellations. The wheel is rotated withi n an envelope that h a s a wi ndow. When t h e wheel i s set for any particular month, day, and hour, the window shows the positions of the constel lations at that time. Every observer should own a good pair of bin oculars. These gather fa r more light tha n the eye; they magnify images and use the capacity of both eyes. Opera-g lass binoculars consist essenti a lly of two sma ll refracting telescopes mounted together. At the front of each is a large lens, the objective, which gathers the light. At the rear is a smaller lens, the eyepiece or ocula r, which does the magnifying. In the front part of the eyepiece is a third element, the erectin g lens, which is necessary to prevent our getting an upside-down view.

B I N OCULAR FACTS

A planiophere: Devices like this

a re h i g h l y u sefu l for l e a r n i n g the various conste l lations.

Optical aid: Binoculars can re· veal l u n a r features and vast sta r fields. (Stellar)

I n the la rge prism binocu lars, the objectives a re centered farther apart. The light rays from them m ust be brought closer together before they reach the eye­ pieces. This is done by a pair of prisms in each tube. Opera g lasses have objectives of a bout one i nch diameter and a magnifying power of 2 to 3. Prism binoc­ ulars, with their larger objectives and higher mag nifi­ cation, a re prefera ble for astronomica l o bserving. Pop­ ular types have objectives of 35 to 50 millimeters (about 1 % to 2 inches), and magnify 6 to 1 0 times. Binoculars labeled "7X 50" mag nify 7 times and have an objective 50 mil limeters in dia meter. The a rea of the objective determines light-gathering a bility; so 7X 50 binoculars gather more tha n 7X 35's. Binoculars vary a lso as to field of view. The field is the whole circular a rea we see through the i nstrument. Thus i n binoculars with a 6° field we can see an a rea of sky 6° in dia meter-eq ual to an area 1 00 feet i n diameter at 1 ,000 feet. Heavy binoculars m a ke the arms tired and un­ steady. The mag nification increases the effect of unsteadiness. Usua l ly 7power g lasses a re the lim­ it for ease i n handling. Bigger ones ordi nari ly re­ quire a support.

Magnification: Large and re· duced sizes of this photo show the Moon as seen with unaided eye and through 7-power binocu­ lars. (Lick Obs.)

,..,....._of ...... Paths of Light t h r o u g h M a g n ifie r a n d Te l escope

Astronomica l telescopes a re of two main types: refracting and reflecting. I n a simple refractor, light is gathered by a lens, and mag nification is done by the eyepiece. There is no erecting lens, beca use this would cut down the amount of light delivered to the eye. The image seen by the observer is inverted, but this ma kes no difference i n observation o f most celestia l objects. With the telescope the observer usua l ly gets severa l removable eyepieces. These a re used for different deg rees of mag nification, as desired . Every good astronomica l telescope has a fi nder-a sma l l telescope, usua lly of 5 or 6 power, with a wide field, mou nted on the main tube. It is used for aiming the telescope, because the field seen through a high­ power telescope is very sma ll. Astronomica l refractors

TELESCOPE P R I N C I P LES

13

genera l ly have a sta r diagonal, a lso, to bend the light at right angles before it reaches the eyepiece. This allows us to observe objects overhead with comfort. Reflecting telescopes use a mirror, not a lens, for the objective. It is a high ly polished concave g lass disk coated usua lly with a luminum or si lver. Light from the sta r fa lls upon this mirror and is reflected to a sma ller diagona l mirror or prism in the tube. This reflects the light to the eyepiece. Refractors get out of adjustment less easily than re­ flectors. less maintenance, such as realignment or the resurfacing of m irrors, is necessary. But reflectors a re less expensive and more readily made by a mateurs. The telescope's ability to revea l faint objects depends mai n ly upon the size of its objective. A lens or mirror 3 inches in diameter wi ll gather two times as much light as a 2-inch, and a 6-inch wi l l gather four times as much as a 3-inch. Figures given in the ta ble here a re only approximate. Some telescopes can do better. Actual performance depends partly upon seeing conditions, quality of the instrument, and the observer's vision. LIG HT-GATHERING POWER

HOW S I ZE O F O B JE C T I VE

DETE R MIN E S

VISIBILITY O F OBJECTS Diameter of Oblec:flve (Inches)

1

Faintest Magnitude* VIsible

9

10

1� 2�

11

11 12Y.a

14 15

4Y.a

7

*See pages

12 13

Number af Stan Visible

117,000 324,000 870,000 2,270,000 5,700,000 13,800,000 32,000,000

2�27 for explanation af magnitude.

Collecting light: A 6-inch mirror, a 50mm. binocular lens, and the human eye differ greatly in light-gathering power, according to area.

The eyepiece of a telescope bends the light rays so that they form a larger image on the retina of the eye than would be formed if no eye­ piece were used . The image size depends upon the foca l length of the eyepiece. The foca l length is the dista nce between the eyepiece and the point at which the con­ verging rays of light meet. The shorter the foca l length, the larger the i mage. Foca l lengths of typica l telescopic eyepieces ra nge from 1.4 inch to 1 V2 or 2 inches. Magnification given by a telescope depends not o n ly upon the eyepiece being used, but a lso upon the foca l length of the objective. The longer the foca l length of the objective, the g reater the magnification obtained with any given eyepiece. To determine the magnification being obtained, we divide the foca l length of the eyepiece into the foca l length of the objective. For example, if the foca l length of the objective is 50 inches, a %-inch eyepiece wi l l give 100 power (" 1 00X "). Theoretical ly, there is no limit to the mag nifyi ng power of a n instrument. Practica l ly, there is. As we use eyepieces of higher pow� r, the image becomes more and more fuzzy, though larger. Fina l ly the fuzzi ness

MAG N I FY I N G POWER

15

becomes so extreme that the object is seen less dis­ tinctly than at a lower power. The practica l magnifying limit depends mainly upon the diameter of the o bjective. For well-made telescopes the limit is a bout 50 times the diameter of the objective, in inches. This means a bout 1 50X for a 3-inch telescope, or 300X for a 6-inch. As the observer becomes familiar with his own telescope, he may find it has a somewhat different limit-say, 40 or 60. The exact figure will depend partly upon the atmospheric conditions. RESOLV I N G POWER The resolving power of a n in­ strument is its a bi lity to show fine detai l-for exam ple, markings on planets. To determine the theoretical resolving power of a n objective, divide the n u m ber 4.5 by the diameter of the objective i n inches. The answer (known as "Dawes' limit") is the distan ce, in seconds of a rc, between the closest objects that can be distinguished. A good 3-inch lens should separate objects a bout 1 .5" (seconds) apart. One second of arc is 1 /60' (min­ ute) or 1 /3600° (degree). A degree is 1 /90th of the dista nce from the horizon to the zenith (point in the sky directly overhead). The average unaided human eye, under good conditions, ca n distinguish stars that a re a bout 1 80'' a pa rt. The performance of a n objective depends upon qua lity of the g lass, optica l surfaces, seeing conditions, and proper a lignment of the telescope. Ma gni fication :

Excessive magni­ fication of an image given by the objective tends to spoil it.

Since it gives such high magnification, a telescope m ust have a strong, steady mounting. The two main types of mounting a re the a ltazim uth and the equatorial. The a ltazimuth mounting is the simpler. It a llows two motions of the telescope-up and down, an "altitude" motion; and horizonta l, an "azim uth" motion. This is a good genera l-purpose mounting. It is light, portable, and easi ly taken down and set up; usua l ly it rests on a tripod. Most telescopes with objectives of less than 3 inches have this type of mounting. The equatorial mounting is designed to be set up in a certain way i n a spe­ cia l ly prepared location, though it too is used for som e sma l l porta ble tele­ scopes. In its sim plest form, the eq uatoria l has two axes at right ang les to each other. It is an a l l-purpose mounting, genera l ly used .,, for serious work. To make the most of it, we m ust set it up properly (page 36). Some equatorials have setting circles, which make it possible to aim the instru­ ment a utomatica l ly at the right point in the heavens (pages 50-53).

TE LESCOPE MOUNTINGS

Resolution: The moon crater Ar· chimedes as it looks well resolved and poorly resolved.

Saturn in a small telescope: Even at 200 to 300X, the planet's imoge is small. But with a good instru­ ment and good seeing, more de­ tails can be seen than appear here. UsuaUy finer details of planets are seen fleetingly, be­ c.ause of atmospheric turbulence. During some years Saturn's rings are "edge on" to us and invisible in small telescopes (see page 91 ) .

Besides the basic equipment that usual ly comes with a telescope, an observer ca n o btain useful extra equip­ m ent. See pages 138-141. Both for serious astronom­ ical work and for plain fun, q ua lity in equipment is a l l­ i m portant. Test instruments before buying. Haziness, m i lkiness, or rai nbow colors in the field a re a sign of poor optica l parts. Good instruments wi l l reduce stars to neat points of light, and show distant print without distortion. If an o bject as viewed "dances" when the telescope is lightly touched, the mounting is below par. A poor mounting spells inconvenience and frustration. Price is not a lways a n indicator of quality. Some low­ cost instruments turn out well, but there is a lways risk i n buying them. If possi ble, the buyer should have the a dvice of an expert. Some buyers exaggerate the im­ portance of "power." They buy the biggest telescope . available at a g iven price-on ly to learn, later, that a smaller i nstrument of better qua lity would h ave given g reater satisfaction. QUALITY OF EQU I PME N T

19

/

/

/

/

Understanding the Sky

/ horizon

A yardful of expensive eq uipment can­ not make up for an ignorance of as­ tronomy. Every observer should have a basic astronomy guide (see pages 1 461 47) and read it. But here is a review of facts that directly affect o bservi hg. Astronomers ca l l the sky, as seen from Earth, the "celestial sphere." It can be imagi ned as a n enormous hol­ low ba ll with Earth at the center, and with the stars on the i nside surface. As Earth rotates, the stars seem to parade by. Exactly what section of sky the ob­ server can see depends partly upon his location. The sky seen from the North Pole is completely different from the sky seen from the South Pole. Between the poles there is a n over­ lappi ng. An observer looking south from New York sees a portion of the northern part of the sky that is seen f�om Rio de Ja neiro. People in Rio can see o n ly the southern part of the sky a rea that is seen from New York.

The celestial sphere (as if seen from outside): Earth rotates from west to east within the sphere. At latitude of New York, stars within 41 ° of the north celestial pole never go below the hori­ zon, and stars within 41 ° of the south celestial pole never rise above the horizon.

21

Big Dipper as seen from d i ffer· ent latitudes: I n central Canada (top) it is higher than as seen at the same time from Long Island (bottom). Here it is near the low point of its revolution.

22

Theoretica l ly, a person at the Eq uator can see the whole sky, but he can see only ha lf of it at once. At night the sky appears to pass steadily overhead, east to west. This seeming motion is due to Earth's rotation. From the North Pole, the sky a ppears to turn like an enormous wheel, counterclockwise, with its hub directly over­ head at the so-ca l led North Star. From the South Pole the sky a ppea rs as a whee l turning clockwise. For an observer halfway between the Eq uator and the North or South Pole, the hub is j ust halfway up (45 °) from the h orizon. Stars within 45 ° of the hub remain in view all night as they m ove a round it. Objects fa rther tha n 45° from the hub rise and set. Objects nea r the center of the wheel seem to move slower than stars farther out. A l l, however, are moving at the sa me speed in degrees-about 360° in 24 hours.

Summer

The Sun 's changing pat h : The path is low in winter, higher in spring and fall, and high­ est in summer. This diagram is far the northern hemisphere. For the southern hemisphere, compass points are reversed. The Moon's path is high in winter, lower in spring and fall, and lowest in summer.

A sta r or planet appears to move at a speed of a bout 1 5 ° per hour a long its circle. But each evening it rises a bout 4 min utes earlier than the evening before. This daily gain is due to the progress of Earth i n its journey around the Sun, and amounts to a gain of a day in the course of a year. Stars that rise and set at any particular latitude, therefore, are n ot visible all year. During some of the year, the time between rising STARS BY S EAS O N S

W h y constellations change with seasons: A s Earth revolves around the Sun, the part of the sky that we see at night changes. During the course of a year, a full circle of the sky passes before our view at night.

Constellations

of

the

Zodiac:

These are drawn as if seen from outside. Constellations in fore· ground are reversed. The Sun is "in" a constellation when be· tween it and Earth.

a n d setting wil l occur dur­ ing daylight. The sta r cha rts on pages 1 48- 157 show that each constel la­ tion, at a given hour, is fa rther west in summer tha n in spring, fa rther west in fa l l than in summer, and so on. Stars are so distant that, though traveling many miles per second, they look m otion less . Constel lations remain the sa me yea r after yea r. Only over centuries could changes in their shapes be noticed by the unaided eye . But all o bjects within our solar system a re much c loser. As seen from Earth, they move against the background of the constellations. The Moon, during most of the yea r, rises an average of 50 minutes later each night, and the height of its path in the heavens changes with the seasons. Posi­ tions of a l l the pla nets, asteroids, and comets change as wel l . The Sun's motion against the background of stars is not so noticeable, but does occur. "FIX E D " STA R S A N D MOVING PLA N ETS

ECLIPTIC AND ZODIAC The path of the Sun agai nst the background of sta rs is cal led the ecliptic. In the course of each day, the Sun moves a bout 1° against the backg round. I n a yea r it ma kes the fu l l circuit of 360 ° .

24

Capricornus

As Earth circles the Sun, its axis stays tilted at a bout 23¥2° with respect to the plane of its orbit. Hence the position of the ecliptic i n the sky appears to change as the year progresses. The ecliptic is directly overhead at 23¥2° north latitude a bout June 2 1 , and overhead at 23¥2° south latitude a bout Decem ber 22. On these dates, the "solstices," Earth is at opposite points of its orbit. All the planets, and the Moon a lso, fol low pathways that remain within a bout 8° of the ecliptic. That is, they follow a n avenue a bout 1 6° wide, with the ecliptic i n the middle. To this avenue the a ncients gave the name Zodiac. Its twelve divisions a re ca l led "signs." 'Y' Aries � Taurus II Gemini

§ Cancer

Signs of

S1... Leo

the Zodiac

llJ2

Virgo

�

Libra

11l..

Scarp ius

t Sagittarius 11.:5' Capricornus

-

Aquarius

* Pisces

25

Ordinarily we describe locations of pla nets with reference to Zodiac con­ stel lations. Th us, "J upiter is i n Pisces" means J upiter is at present i n the a rea of sky outlined by Pisces. The mag­ nitude of a celestial body is its brightness, compared to a certain sta nda rd, as seen from Earth . Magni­ tude depends upon the amount of light the object emits and upon its distance from Earth . Some sta rs vary in mag nitude beca use their light output changes. Planets va ry as their dis­ ta nce from Earth changes. Magnitude 1 is 2% times the brightn ess of magni­ tude 2; magnitude 2 is 2% times magnitude 3; etc. Thus, a sta r of magni­ tude 1 is 6.3 times as bright as a star of magni­ tude 3, and 1 6 times as bright as a star of magni­ tude 4. Some objects a re of "minus" magnitudes. Th us, the Sun is of mag nitude - 27; fu l l Moon, - 1 3 . MAG N ITUDES

Asteroid trail: For this time expo­ sure, a clock drive kept the tele­ scope trained on the same field despite Earth's rotation. The aster­ aid, moving against the back­ ground of stars, made a trail. (Yerkes Obs.) Magnitudes: Magnitudes of many stars can be estimated by compar­ ison with stars of known magni­ tudes in the Little Dipper and Southern Cross.

· · � 1 "' •

•

.

�

.

./·� .

�/ •

.

E ffed of increasing power: At left is a 7° field in Cygnus as seen with 7x50 binoculars. At right, centered on the same star, is the re­ duced and inverted field seen through a small telescope at about 35X. Numbers on map indicate magnitudes of stars (decimal point before last digit omitted).

Mag nitudes a re sometimes rounded off: Magnitudes from

-1 .5 -0.5 + 0. 5

Are Considered to

-0.6 +0.4 + 1 .4

as Magnitude

-1 .0 0.0 + 1 .0 etc.

On a clea r, dark nig ht, the unaided eye may detect sta rs as faint as magnitude 5 or 6. Binoculars help us to see "down" to magnitude 8 or 9, and a 6-i nch telescope to a bout 1 3. The brightness of planets changes according to their positions with respect to Sun and Ea rth . Planets outside Earth's orbit a re brightest when Ea rth is between them and the Sun. The mag nitude of Ma rs, for exa m p le, varies from - 2.8 to + 1 .6, and J upiter from - 2.5 to - 1 .4. Planets shine more steadily than do sta rs. Light from a star reaches us as if from a tiny poi nt, and atmospheric i nterference with this thin stream of light is q uite notice­ able. Light from a pla net comes as if from a disk; the strea m is thicker and the atmosphere has less effect. 27

First Steps in Observing loca l conditions a lways put a limit on what a n observer can see. Faint sta rs become lost i n the glow of city lights. Heavy traffic o n a nea rby street may ca use a sta r image in one's telescope to shiver. If the telescope is pointed at a planet that a ppea rs just over a neigh bor's roof, heated air rising from the roof may turn the planet's image i nto a "boi ling" blob. Gusts of wind, clouds sudden ly rol ling in, and inconven iently located trees are oth er haza rds. The observer with a broad, open horizon, free from interfering lights, is lucky. City observers someti mes m ust retreat to a park to see more than the Moon or a few bright sta rs. The suburba nite must place his telescope so that a building or hedge wi ll block the light from a neigh bor's livi ng room or front porch. U n necessa ry discomforts ca n q uickly spoil the fun of observi ng. In winter, warm clothing is vita l . In summer, a mosq uito repellent may be necessa ry. In any season, a stool or chair wi ll spell comfort during long periods at the telesco pe. For observers using binoculars, a re­ clining chair ma kes it easier to observe objects high overhead. The scattered, puffy cumulus clouds of a fai r day usua lly vanish soon after sunset. Stratus and cirrus clouds, often associated with rainy weather, are more likely to linger. Oddly enough, the clea rest night is not a lways the best for observin g . The atmosphere may be q uite turbu-

S E EING CONDITIONS

The Pleiades: An open cluster of six stars t o the unaided eye, the Pleiades become in binoculars a glittering spray. Telescopes of 6 inches and more show that the cluster is em bedded in faint clouds of glowing gas, noticeable in this photograph. (MI. Wilson and Palomar Obs.)

29

"Seeing": Turbulence in the atmosphere (left) usually means poor seeing, with "boiling" star images (see inset). A quieter atmosphere (right) usually allows better seeing. The stars usually twinkle most on a very clear night, indicating more than the usual turbulence.

lent. Differences in density between warm and cold air cu rrents ca use light to be refracted, or bent, i rregu larly as it comes down through the atmosphere. The images seen i n the telescope then uboil.u A slightly hazy sky, with relatively sti l l air, is preferred . The nearer a celestial object is to the horizon, the less clearly it will be seen, usua l ly. Its light comes slanting through Earth's atmosphere and thus passes through more distu rbing air currents and d ust than does light from a n object higher in the heavens. Moonlight, too, i nterferes, and by the time the Moon is fu- 1 1, only the bright sta rs can be seen . A s w e leave a lighted house, o u r eyes begin adapting t o t h e darkness. After a few min utes we ca n detect objects severa l times fainter than at fi rst. Th ereafter, our ability to see in the dark improves slowly for hours. But to keep this sensitivity, we avoid looking at bright objects. Any light used during observation, such a.s for consu lting star charts, should be dim, and it should be red. (Red impairs sensitivity of the eye to light

US I N G O U R EYES

30

less than other colors.) A small red Ch ristmas-tree light on a n extension cord, or a flashlight covered with red cloth or cellophane, wi ll do. To detect faint objects, experienced o bservers often use "averted" vision. They look a little to one side of the object, so that its light wi l l fa l l on a m ore sensitive part of the retina. C E LESTIAL O BJECTS Since conste llations a re the observer's sig nposts, every observer should know the principa l constel lations visible at his latitude. The cha rts on pages 1 48- 1 57 show a l l the constel lations and the ti me of the year when each is conveniently located for seeing. Constel lations ca n be lea rned by using either these charts or a planisphere (page 1 1 ). Once they have been learned, it is easy to locate the brighter sta rs and planets. Fi rst we fi nd the constel lation in which the object is known to appear. Then we narrow the hunt down to the right part of the constel lation. Suppose the observer wa nts to find the great red star Betelgeuse. He looks it up in the index of this book, which refers him to the chart on page 1 50. There he sees that Betel­ geuse is at the northeast corner of a g roup of bright FINDING

Signpost: Conste l lations can b e g u ides t o faint celestia l objects. This time-exposure p hoto of Orion shows faint sta rs invisible to u n ­ a i d e d eyes. (John Polgreen)

stars forming the constel lation Orion. The chart shows Orion in relation to the other constel lations, and the ti me of year when it is conveniently visib le. With this i nformation, the observer fi nds Orion i n the sky (if the time of year and time of night a re right), and Betelgeuse is identified. Betelgeuse is easy to spot because it is red and promi­ nent. Most sky objects are fai nter and tend to become lost i n the m u ltitude of stars visible in binoculars and telescopes. To find a faint object, we m ust fi rst identify bright sta rs near it and then use these as g uides. Their positions are easier to hold i n mind if we notice the patterns they form-sq ua res, triang les, circles, loops. Suppose we want to get a look at the famous sta r c luster M 1 3 in the constel lation Hercu les. The chart (page 1 55) shows it is located on a n almost straight line be­ tween two sta rs forming the west side of a "keystone" at the center of the constellation. We find the constellation and the keystone. With reference to the North Sta r, we decide which is the west side of the keystone. Then, with the help of binoculars (because the object is very faint), the cl uster M 1 3 is spotted. EST IMAT ING TANCES

SKY

Observers

Dis­ get

accustomed to measuring sky The

distances in degrees. distance

from

the

zenith (point in the sky exactly overhead) to the M13: This cluster, faint Ia u n a ided eyes, is hard to find u n less one knows just where to look. I t ap· pears l ike this in a telescope. (Mt. Wilson and Palomar Obs.)

Reference constellation: I n n o rth­ ern latitudes, Big D i p p e r is a handy g uide. Dista nce between Pointers (fo r m i n g outer end of bowl} is about 5°. Dipper revolves a ro u n d north celestia l pole i n 23 hours 56 m i n u tes.

horizon is 90° ; half of this distance is 4S0; and so on. By this standard the dis­ tance between the two brightest stars in the bowl of the Big Dipper, the "Pointers," is about S0• In the southern sky, the span between the two stars forming the leg of the Southern Cross (Crux) is a bout S 0 a lso. By referring to these spa ns, one ca n estimate dista n ces elsewhere in the sky. Binoculars, too, make a good yardstick. In binoculars with a 7° field, for insta nce, the diameter of the circle of sky shown is a lways 7°. We can measure long dis­ tances across the sky by 7° steps. In telescopes, size of field (page 12) varies according to the power of the eye­ piece being used. The field may be somethi n g like %0 with the %-inch eyepiece, or 1 ° with the 1 %-inch. To determi n e the field obtained with each eyepiece, point the telescope toward any prominent, concentrated group of stars near the equator. look through the eye­ piece and note the stars at opposite sides of the field; then check your atlas to determine the dista nce i n de­ g rees between these stars. This dista nce is the field given by the eyepiece. The eyepiece field can be determined a lso by noting how long it takes a star near the equator to cross the field. The motion is 1,4 ° per minute. 33

Holding a sta r chart: Chort is rotated until the star pot­ terns correspond to their ac­ tual positions in the sky.

SKY DIRECT I O N S To avoid confusion as to sky directions, these m ust be thought of with respect to the celestia l pole. I n the northern hemisphere we refer to the North Star, which is a bout 1 ° from the true pole. Suppose you have found Betelgeuse in Orion and want to find p. Orionis, a fainter star in the sam e con­ stel lation. A star atlas shows that p. Orionis is a bout 2° north and 1 ° east of Betelgeuse. Looking at Betel­ geuse again, you menta l ly draw from it a line to the North Star. This line is i n the direction of north. At right ang les to north, and in the direction from which the stars are moving, is east. With your menta l yardstick or with binoculars, you measure 2° north and 1 ° east from Betelgeuse, and there is p. Orionis. Directions are most easily confused near the celestia l pole. Remember: t h e motion o f stars in t h e northern hemisphere as they revolve a round the pole is counter­ clockwise. As you face north, the stars over the celestia l pole a re moving westward (towa rd your left) a nd the stars below the pole are moving eastward (towa rd your right). I n the southern hemisphere, stars revolve clock­ wise around the pole. When using a chart, hold it u p toward the sky in the direction i n which you a re looking. Rotate it unti l the star pattern on the map matches the pattern as you see it in the sky.

34

Using a Telescope Our fi rst look through a telescope at the Moon or a sparkling sta r cluster ca n be exciting indeed. But in the long run, the fun of sky observing depends upon our increasi ng ski l l with the telescope. Even a sma l l instru­ ment, if it is a good one properly used, can perform superbly and g ive tremendous satisfaction. Telescopes a re ordinarily kept dismantled. The ends of the tube a re usua lly covered with dustproof bags or caps. Eyepieces are kept in a dustproof box. Getting a si mple a ltazim uth telescope ready for use is usua l ly just a matter of setting up the tripod or base Orientation of an Equatorial Telescope

Tube Pointed

Tube Pointed T award

at Celestial Pole

Equatorial Region

35

Jovian portrait: This photo was taken through a large tel­ escope. In a small telescope the image is much smaller but these details are deor. Even with a small telescope one can notice the planet's equatorial bulge, its rotation, and the movements of its satellites. Note satellite (upper right) and its shadow on planet's disk. (Mt. Wilson and Palo­ mar Obs.)

and attaching the tu be to it. The location shou ld be level, and where neigh borhood lights, trees, and bui ldings wi l l not interfere (see page 29). If the telescope is put on a platform or ta ble, this m ust be firm. The legs of a tripod m ust be securely set to prevent sliding or vi bration. With a n equatorial telescope, set up the tripod or base fi rst, then attach the counterweig ht, and fi na l ly fasten the tube in the crad le. In dismantling, the tube is removed first, then the counterweight. For safety, a heavy telescope should be disassembled before bei ng moved from place to place. Both a ltazim uth and eq uatoria l telescopes can be set up and used i n a ny position. But the equatorial will work better if the polar axis points approximately to the celestial pole. For best resu lts, set up the telescope in this way: Place the pedes­ ta l or tripod legs on the ground so that the polar axis points directly at the celestial pole. (In the northern hemisphere, the pole is a bout at the location of the North Sta r; see chart, page 1 49.) Clamp the declination

ORIEN T I N G AN EQUATO RIAL

36

axis to prevent motion on that axis. Then, to check the a lignment, look th roug h the finder as you move the tube back and forth on the polar axis. If the pole remains near the center of the field in the fi nder, the alignment is good. If the a lignm ent is poor, it ca n be improved by slight readjustments of pedesta l or legs. The a lignment is good enough when the pole stays withi n a degree of the center of the field in the finder while the tube is moved on the polar axis. Mark the pavement or ground in some way so that the pedesta l or legs can be set up with less fuss next time. Properly placed, the equatorial is easy to use. With both axes undamped , there is free m otion in any direction. With the polar axis clam ped, there is north-and-south motion on ly-con­ venient for scanning the sky as the Earth rotates. With the declination axis clam ped, there is east-and-west motion on ly. Thus you ca n keep the telescope trained on an object for a long ti me simply by moving the tube around the polar axis to compensate for Earth's rotation. You r hand or a clock drive (page 138) can provide this m otion. MOT I O N S O F THE EQUATO RIA L

Altazimuth mounting: Following sky objects as Earth rotates is not so easy with this mounting as with an equatori a l . But a n altazimuth con give good service. Note use of star diagonal , needed with refractors for viewing objects high above horizon.

EYEP I E C E

SELE C T I O N

Most telescopes come pro­ vided with three eyepieces for sky observing. An ad­ ditiona l one may be in­ cluded for terrestria l ob­ serving, beca use celestial eyepieces invert the image. The terrestrial eyepiece is not used for sky observi ng, Ma gnification vs. field: A Moon because the additiona l crater as seen with eyepieces lenses req uired to make the image upright reduce the a mount of light received by the eye. In the eyepiece holder is an adapter-a meta l tube. Into this the eyepiece is inserted, then moved back and forth unti l you find the position that gives the best image. With a refractor, the star diagona l is used for ob­ serving objects high in the sky. Insert one end into the adapter; i nto the other end goes the eyepiece. I n some refractors the diagona l must be used at all times to get the eyepiece far enough out for proper focus. Beginners tend to use their most powerful eyepiece too much. Seasoned observers know that magnification is not all-importa nt. They choose the eyepiece that wi l l do t h e particular j o b best. If a wide fi e l d o f view is needed, use a low-power eyepiece. Low power is pre­ ferred when "sweeping" la rge a reas of sky (as for comets or novas), when looking at wide sta r clusters such as the Pleiades, or when viewing the whole moon rather tha n just part of it. Low power i� best a lso for h u nti ng an unfamiliar faint object; a more powerful eyepiece ca n be substituted after we have found it. 38

giving low, medium, a n d high power (left to rig ht). As magnification is increased, the field and fineness of d etail decrease.

High power is needed for splitti ng c lose double sta rs, seei ng lunar details and pla net features, and detecting individual sta rs i n close-packed clusters. Since high power tends to da rken the sky background, it helps us to detect very faint objects. However, as we use in­ creasing power on a n object, details lose sharpness. Specia l eyepieces have been designed for safe direct observation of the Sun. See page 67. An accessory that many sky observers have found very satisfyi ng is the so-ca lled Barlow lens. This is used i n combination with any eyepiece t o increase mag nifica­ tion. At the sa me time it cuts down the f1eld. An observer should learn the f1eld of view given by each of his eyepieces. For an easy method see page 33. Observing conditions put limits on telescope perfor­ mance. The fai ntest magnitudes that we ca n detect vary. One night we may be able to use 350x on a n object before it "comes apa rt," a nd the next night the limit may be 200x. Some evenings we "sp lit" the double sta r Castor with 1 25x, and at other ti mes the seei ng may be so poor that 250x wi ll not do it. 39

R e gion of nebulas: From this area near the star Eta Carinae in the southern heavens comes much radio "noise," which is picked up by radio telescopes. The illumi­ nated nebulas and the many dark nebulas, some of which are no­ ticeable here, are interesting to trace with optical telescopes. (Harvard Obs.)

TELESCOPE

S I G HTING

Sighting a telescope by poi nting the tube is usua l ly not accurate enoug h . Ord­ inarily we need to use the finder. This is likely to have a field (inverted) of 5° or 6°. If the fi nder has been exactly lined up with the tube, a n object centered i n the finder will be found to be centered in the eyepiece too. Sighting bright objects through the finder is easy. But for faint objects the step method may be necessary. Consu lting our chart, we note the object's position with respect to the nearest bright stars. Using these as sign­ posts, we work our way to the object sought. As the tube of a reflecting telescope is moved, it may have to be rotated on its longitudinal axis i n order to keep eyepiece and finder in positions comfortable for viewing. I n all good reflectors a rotata ble tube is sta nd­ ard. I n refractors the star diagona l a l lows comforta ble viewing in any direction. Experienced observers have the ha bit of esti mati ng dista nces across the sky in terms of degrees, and of using the celestia l pole as the key to directions. Dista nces between stars ca n be estimated easily with the help of the finder (page 33). 40

A sector of sky seen in the finder or eyepiece is mag­ nified as well as inverted. It differs from the sa me part of the sky as seen by the unaided eye. The begin ner may find this confusing, but sighting becomes much easier with practice. Observing with a telescope is a consta nt test of our eyes-a nd of our ski l l in using them. A good observer does not sta re hard a n d long through t h e telescope; he looks carefully but briefly. long, hard looking causes fatigue and loss of visua l

MAKI N G THE MOST O F EYES I G H T

Finder and Eyepiece on a Refractor

Finder and Eyepiece on a Reflector

1\Jbe

41

Seein g detai l on planets: This painting, seen in normal light at a distance of about 40 feet, sug­ gests the appearance of Mars in a small telescope.

s e n sitivity. A s e as o n ed planetary observer may watch half the night for those few seconds when the seeing is good enough to reveal some delicate detail, such as a "cloud" or a "ca nal" on Mars. Rests a re essential! When looking into an eyepiece, keep both eyes open. That means less fatigue for both eyes. You soon learn to concentrate on what the observing eye sees. When seeking a very faint object in the field, or very faint details on a n object, look a little to the side. Averted vision ma kes use of the more sensitive part of the reti na. When comparing sta r magnitudes, variable-star ob­ servers keep i n mind that the eye is particularly sensitive to red. Red bui lds up on the retina as light bui lds up on photographic fi lm . A red sta r, looked at steadi ly, seems to get brighter. Never look at the Sun without proper precautions! (See pages 66-67.) The fi rst experiences of a beginner in hand ling sta r charts may be confusing and exasperati ng. The star field on the chart never looks q uite like the same field as seen through the finder or eyepiece. The two fields are likely to differ in sca le. I n the telescope the observer probably sees more stars than appear on the chart at hand. Fina lly, depending on HA N D L I N G STAR C HARTS

42

the make-up of the instrument, the field as seen in the eyepiece may be reversed or inverted, or both. Some telescopes change the field i n such a way that, to use the chart, we m ust look at its reverse side while holding it against a lig ht. Even the experienced observer is sometimes confused, but the beg i n ner should not get discouraged . With a little experimenting he soon learns what happens to a star field in his instrument. The method that usua lly works is si m p le: look at the sta r chart and choose a bright sta r near the object being sought. Using the fi nder, poi nt the telescope at this star. look i nto the eye­ piece, identify the star, and notice the figure it forms (triang le, arc, etc.) with neigh boring stars. Then hold the chart so that the figure there is i n the same position as i n the eyepiece. Holdin g a star chart: In the northern hemisphere, when the observer is facing east, the N side of the chart is toward his left, in tbe direction of the north celestial pale. When facing south, the N side is up. Facing north, the N side is up or down depending on whether the field is above or below the pole. FaCing west, the N side is toward the right. In the southern hemisphere, the procedure is the same, except that when fac­ ing south, the 5 side is toward the pole.

Rieht ncention and decli­ nation: Celestial sphere Is mapped by -n• of lines Indicating right -nsion and dedlnatfon. Lines of rleht a-sian correspond to -'dlans, or llna of longitude, on Earth. Lines of dedlnatlon corr01p0nd to lines of latitude. This dla· gram represents only half of celatlol sphere, as -n from center; other holf -ld show llna of right asconslan from VI to XV I I I.

Star Charts and Setting Circles Sta r charts a r e t h e astronomer's maps. With t h e m he locates stars and other objects whose positions on the celestia l sphere change little from year to year. O n t h e m he p lots courses o f S u n , planets, and other objects whose positions change more noticea bly. like maps of Earth's surface, star charts a re prepared according to different sca les to show varyi ng amounts of detail. The charts on pages 1 48- 1 57 are limited mostly to sta rs and other objects that can be seen with unaided eye and binoculars. The limit is, for the most part, a bout 5th magnitude. Special charts showi ng all the stars that can be seen with sma l l telescopes have to be much m ore detai led; some include objects to a magnitude of 1 3 or 1 4. A set of charts detai led enough to show a l l stars visible in binocu lars ma kes a siza ble atlas. Southern Cross and Coal Sack in Milky Way (left)

_

(Harvard Obs.)

45

looking north: If lines of right as­ cension and decli'nation were printed on the sky, an observer in the north­ ern hemisphere , looking north, would see a "wheel" (partly shown here). As Earth rotated, the wheel would turn counterclockwise and the "hours" (shown by Roman numerals) would increase clockwise. In a diagram for the southern hemisphere, the wheel would turn clockwise, and "hours" would increase counterclockwise.

STAR D ES I G NATIO N S A N D NAMES T h e bright stars on most charts a re designated by Greek letters:

a

Alpha Beta y Gamma ll Delta e Epsilon K Zeta

f3

'I 8

Eta Theta

1 Iota p Rho " Kappa u Sigma X Lambda r Tau p. Mu v Upsilon v Nu ¢ Phi X Chi � Xi o Omicron ,.t. Psi w Omega 'IT Pi

Except for a few examples such as Castor and Pol lux, in Gemini, the brightest star in a constellation is given the letter a, the next brightest {3, and so on. Ancient sky observers gave names to the stars. Our modern charts retai n the Greek letter designations and name o n ly the brightest stars, such as Sirius, Procyon, Arcturus, Betelgeuse. To identify a star, we may simply use its name, such as Betelgeuse, which everyone knows is i n the constel lation Orion. However if we designate the sta r as a, we write or say a Orionis, using the Latin genitive of the constel lation. 46

Most star charts, such as those in this book, have a g rid of vertical and horizonta l lines, indicating right ascension and declination . These cor­ respond to the geogra pher's lines of longitude and latitude. The li nes of right ascension are d rawn between the celestial poles, and the lines of declination a re drawn a round the celestial sphere parallel to the celes­ tia l equator. J ust as any city on Earth ca n be located by statin g its longitude and latitude, so any object on the / celestial sphere can be located by its rig h t ascension and decli nation .

S KY COORDI NATES

47

Declination, or distan ce from the celestia l equator, is measured in degrees and min utes. Declination north of the celesti a l equator is indicated by a plus ( + ) sig n ; south, b y a minus t - ) sign. Right ascension is measured in hours, min utes, and (if necessary) seconds, from 0 to 24 hou rs. It is measured eastward from a meridian that passes between the celestial poles and th rough the vernal equinox. The verna l equinox is the point where the Sun crosses the celestial eq uator in its a pparent northward journey in March each year. The right ascension (" RA ") and declination ("Dec") of an object can be written very simply, in the form of 48

Looking south : In the northern hemi­ sphere, looking south, we can imag­ ine this pattern of coordinates on the sky. Motion of stars is from left to right. South celestial pole is below the horizon. For a southern-hemi­ sphere observer looking north, hours increase left to right and north celes­ tial pole is below horizon.

what astronomers cal l "co­ ordinates," thus:

a Canis Majoris

RA

(Sirius) .............. 6• 43m

a Orionis

(Betelgeuse)

...... s• 52 m

Dec

- 1 6 ° 391 + 7°

241

The coordinates of any star, star cluster, or nebula ca n be read from a sta r map sim p ly by looking at the lines of right ascension and dec­ li nation. Coordinates of most of these objects change little over periods of years. But co­ ordinates of planets, comets, and other objects in the solar system, which are relatively near us, do change regularly. They m ust therefore be obtained from a l� manacs and other up-to-date publications. Suppose we want to have a look at the sta r Foma lhaut. We don't know wbat con­ stellation it is in, but we do know its right ascension is 22 • 55m, and its declination - 29° 53'. We find a star chart (page 1 54) with lines of right ascension and decli nation near to the coordinates of Fomalhaut. On this chart Foma lhaut is found easi ly i n the constel lation

US I N G COORDI NATES

49

1 9h

1 8h

1 7h

Finding M 1 3: Section of a

star map indicates how bright stars can be used for locating faint objects. To find M13, find Vega, then find the "square" of Hercules to the west. For a more �etailed explana­ tion, see text on facing page.

Piscis Austrin us. Then, with the help of the chart, if necessary, we find the constel lation i n the sky and identify Foma lhaut. Now we spot a faint comet in the constel lation Cas­ siopeia, and we want to report it. Noting the position of the comet with reference to stars in the constel lation, we plot the position as precisely as possi ble on a star chart. Then, by reference to the lines of right ascension and declination, we determine what the coordinates of the comet are. The discovery of the object can then be reported with a fair degree of accuracy, depending on the sca le of the map used. CIRCLES Ma ny eq uatorial telescopes are equipped with setti ng circles. With these we can make direct use of coordinates at the telescope, if it has been set up properly (see pages 36-37) . The so-ca lled hour circle corresponds to right ascen­ sion; it is ma rked for hours and min utes. The other circle, which indicates declination, is ma rked for deg rees and min utes of arc. To i l lustrate one way of using circles, suppose you are seeking that faint sta r cluster M 13, in Hercules. SETTING

50

Your star atlas shows Vega as the nearest bright star; so you use Vega as the starting point. The chart gives: RA

Vega ................ . . . . .............. . ........... 1 8h 35m M 1 3 ................................................ 1 6h 40m

Dec + 38 ° 44' + 36 ° 33 '

Su btracti ng, the dista nce from Vega to M l 3 is 2 ° 1 1 ' i n Dec southward, a n d l h 55m i n R A westward . Now get Vega in the center of the field and clamp the RA axis. Watching the Dec circle, m ove the tube 2 ° 1 1 ' southward. Then clamp the Dec axis and unclamp the RA axis. Watching the hour circle, move the tube 1 h 55m i n RA westwa rd. That should bring you to M 1 3. This method usua lly works well enough to bring the desired object i nto the field of a low-power eyepiece­ say, a l -inch. If the telescope is properly pointed, higher power can be used, if desired. Another method of using setting circles involves the use of siderea l time. The siderea l time (ST) at any moment is equal to the RA of any star that is on the observer's meridian at that moment (see pages 1 36- 1 37). To determine the siderea l time, pick out some familiar star on or near the equator whose RA is known. The Setting circles: With these, a telescope is easily sighted .

sta r should be slig htly east of the meridian. Point the telescope due south and clamp it in declination equa l to the Dec of the star. Watch the field of view, and when the sta r is observed i n the center set your watch or a clock to agree with the RA of the sta r. This wi l l serve as a siderea l clock for the evening. When the circles are properly adj usted, the RA circle will read o• when the teiescope is pointed due south . Then, to find any star, simply find out how far the star is from the meridian: that is, its hour a n g le (HA), east or west. The HA ca n be obtained by fi nding the difference between the ST a nd the RA of the sta r. (Remem ber: siderea l time is reckoned conti nuously from 0 to 24 hours.) If RA is greater tha n ST, HA is east of the merid­ ia n. If ST is greater tha n RA, HA is west of the meridia n. Assume you want to sig ht the star Algieba (y Leonis) in the constel lation Leo. You have the followi ng: RA l Oh 1 7m, Dec 20°06', ST 07h 37m. Since RA is greater than ST, subtract ST from RA and get HA 2h 40m east of the meridia n . That is, the sta r is 2h 40m east of the meridia n. Now as­ sume ST is 1 3h som, which is 3h 33m g reater than RA. The HA (or star) is that fa r west of the meridian . Elusive objects: I n time exposu res mode at observatories, many neb· ulas such as this one (M8 1 in Ursa Major) become strongly p romi· ne nt. As seen i n small telescopes they a re usua l ly faint. (Mt. Wilson and Palomar Obs.)

For the telescope: This portion of chort used by observers of vorioble stars covers a n a rea i n Triang u l u m . Divisions a re a bout 1 ° squa re­ a typical field in a small telescope. Dots a re stars; magnitudes are given with decimal poi nts omitted . Under best conditions, only two sta rs wou ld be visible to unaided eyes-those marked 58 ond 56. Strong (50mm) binoculars might detect sta rs as fai nt as 95. A 3-inch telescope wou l d be needed for 1 1 6. (AAVSO)

Once you have the HA, clamp the telescope in the declination of y leonis ( + 20°06'). Then unclamp the RA axis and turn tube east or west (as the case may be) to desired a n g le on RA circle, and there is Algieba. A different method of finding an object is possi ble if the telescope has a mova ble hour circle ma rked from Oh to 24h. Get a brig ht sta r in the center of the field. Turn the circle to read its RA. To fi nd the object, turn the telescope unti l the circle reads the RA of this object. 53

Earth's nea rest neighbor: This composite of the Moon, showing details with exq uisite clarity, was made by combi n i n g photog raphs taken at fi rst a n d last quarter. The shadows on the opposite hemispheres d iffer i n d i rection. The Moon at full phase would look flat, show little de· tail, because of lack of shadows. (Lick Obs.)

54

The Moon T h e Moon i s o u r nearest neigh bor, except for certai n asteroids a n d man-made satellites. This bleak, airless sphere is a bout 2, 1 60 mi les in diameter, and revolves around Ea rth at an average dista nce of some 238,857 mi les, completi ng one revolution in a bout 27 days. The lunar orbit is an ellipse, not a true circle; so the distance of the Moon from Earth changes. Since the Moon rotates on its axis i n the sa me time it ta kes to revolve around Ea rth, the lunar hemisphere visi ble to us remains a bout the sa me. Librations (appar­ ent tilting due to the Moon's motions with respect to Earth) make a tota l of about 59 per cent of the lunar surface visi ble each month. LIGHT O F T H E MOON Sunlight fa lls on the Moon as it does on Earth. But the Moon has no atmos­ phere to fl lter the flerce rays. The lunar surface in day­ lig ht, therefore, gets intensely hot-something like 250°F., or h otter than boi ling water. (The dark side proba bly gets to 243 ° F. below zero!) What we ca l l "moon light" is simply sunlight which t h e Moon is reflect­ ing towa rd Ea rth. Except during lunar eclipses, a full half of the Moon is a lways lig hted by the Sun. But we see this fu l l half only when Earth is between Sun a nd Moon-the phase cal led full Moon. When the Moon is not in line with Earth a n d Sun, we see o n ly pa rt of the lighted half. J ust after n ew Moon, a thin bright crescent is seen . The rest of the disk is faintly lighted. This faint light, ca l led "the old Moon in the new Moon's arms," is light reflected from Earth to the Moon's dark side, and is known as earthshine. The Moon rises a bout 50 minutes later each night THE

55

L u n a r h a l o : Refra c t i o n of moonl ight by ice crysta ls i n high atmosphere produces this spec­ tacle. Usually the halo is of 22° rad ius, sometimes 46° .

on the average, but the actual time from month to month varies consid­ era bly. For some eve­ nings around fu l l Moon nea r the a utu m n a l equi­ nox (a bout September 23) moon rise will be only about 20 min utes later each night, beca use the angle between ecliptic and horizon is then near the minimum. Thus we have moon­ light in ea r ly evening longer than usua l . This phase is ca l led Ha rvest Moon . The next fu l l phase after Ha rvest Moon is known as H u nter's Moo n . T h e lunar pathway stays n e a r t h e ecli ptic, or path of the S u n . However, while the Sun rides high in summer and low i n wi nter, the Moon rides low i n summer and high i n winter. At the fu l l phase, the lunar disk may ta ke odd shapes as it rises or sets, pa rticula rly when seen through a dense or smoky atmosphere. Sometimes re­ fraction ma kes it look ova l . T h e M o o n i s o n e of t h e most satisfying objects f o r the amateur. The best times to observe are between last and fi rst quarter; then there is less g lare. The shadows of the mou ntains and in the craters a re longest and set off the rugged landsca pe in sha rp relief. Often the Moon can be we l l observed during daylight hours. When beyond the crescent stage, the Moon reflects considera ble light. For eye safety during prolonged 56

telescopic observing, a fi lter should be used over the eyepiece, or a fi lter cap placed over the objective, or the a rea of the objective red uced by placing over it a ca rdboa rd cap with a hole of the desired size. (See pages 67 and 1 39- 1 40.) Another way to cut down g lare is to use a n eyepiece of high enough power so that o n ly pa rt of the Moon is in the field of view. Then less light reaches the eye. After a period of lunar observing, the sensitivity of the eye to fai nter objects is m uch reduced. Pla n o b­ serving sessions according ly. Some mou ntain ranges, seas, and craters can be seen even with binoculars. Much more can be seen with a sma l l telescope. With a 3- or 4-inch i nstrument, use a lower power-30 to 1 OOx. Don't use power beyond what atmospheric conditions a llow. For serious lunar work, a 6- or 8-inch telescope is needed, with a power up to 300x or 400x. This wil l clea rly show details o n ly a half mile a cross. Atmospheric effects: The Moon moy o ppeo r reddish ond fl attened when neor the horizon, because then the light comi n g from it to us has a longer path through the atmosphere. Red rays penetrate the atmosphere more easily than others. Refraction causes the flattening .

SOUTH

THE

MOON

Mountains, Valleys, and Scarps

A

8 C D

E F G H

EAST

TtlfSCOpt, (£)

SuM on a more detailed map published b) copyright 1 9.56 and

bi Sky Sk,

Pllbfi$hlng Corp. , Clmbrldge, Mass.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

A l p i n e Valley Alps Altai A p e n n i n e Mts. Carpath i a n Caucasus Haem us Harbinger

I J

K l M N 0 P

.

Hyg i n u s C l eft J u ra Mts. Pica Pyrenees Riphaeus Straight Range Straight Wall Teneriffe

Craters Agrippa Al boteg n i u s Alphonsus Apionus Apollonius Archimedes Aridarchus A r istil l u s A r istote les Arzachel At lao A utolyc u s Bayer Bullialduo Burg Cossini Catharine Clavius Cleomedes Colombo Copernicus Dawes Encke Eratosthenes Eudoxus Fabricius Flamsteed Fracostorius Franklin Gasse n d i Gauricus Geber Gemma frisius God in Good acre Grimaldi Hell Heraclitus Hercules Herschel Herschel, J. H eve l i u s

43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83

H i pporchus lsidorus Julius Caesar Kepler lambert licetus Linne long omonta nus Mocro b i u s Magin u s Manilius Me rcator Messier Moret us Newton Oronti u s Pallas Petovi us Picard Pickering, W. H. Plato Plinius Posid o n i u s Ptolomaeus P u rbach Pythagoras Rabbi levi Regiomo nta n u s Reinhold Ricci a l i Sacrobosco Schiller Snel l i u s Stevi n u s St6fle r Theaetetus Theo p h i l u o Tycho Vitruvius Vlacq Walter

Copernicus: Mountain-ringed plain

(right) has eight peaks; one is 2,400 feet high. Note rays around Cope rnicus; also 11d rowned" era· ters (high center). (Mt. Wilson and Palomar Obs.)

On the dry lunar su rface, mountains rise to heights of over two m i l es, a nd among the numerous craters are some as wide as 60 a nd 70 mil es. Vast flat a reas-the ma ria, or "seas"-are visible. Great mountain ranges such as the Apen nines, Alps, and Caucasus, a re a lways of interest. Numerous craters de­ serve special attention-Plato and Archimedes, Coper­ nicus and Tycho and Kepler. There a re the long, straight T H E LUNA R LANDSCAPE

Phases o f t h e Moo n : A t a l l times, a f u l l hemisphere o f t h e Moon is

lighted by the S u n . How much of the lig hted a rea we ca n see at any time depends upon the position of the Moon i n its orbit at that time. I n the no rthern hemisphere, the Moon appears to g row from right to left, as i n this diagram (bottom). In the southern hemisphere i t g rows from left to right. The full cycle covers 29 days 1 2 hours 44 m i n utes.

Straight Wall: This steep escarp­

ment (near center), about 80 miles long, probably resu lts from a fau lt in Moo n ' s crust. The "drowned" craters (lower right) we re perhaps fi lled by lava flows. (Lick Obs.)

cliffs; deep, narrow, or crooked va lleys; wide cracks sometimes extending hundreds of mi les; light-colored strea ks or rays extending from some of the craters, the most . striking of which are those from Tycho. I n 1 650 the astronomer Riccioli produced the fi rst map of the Moon. He is said to have originated the system of naming that we use today. The g reat plains or flat areas are cal led "seas" (Ma re Nubium, Sea of Clouds; Mare Im brium, Sea of Rains; and so forth). Most of the mountain ra nges bea r some resem bla nce to those on Ea rth, such as the Alps and Apen nines, and are named after them. Conspicuous craters bear the names of ancient phi losophers and of as­ tronomers-Plato, Archimedes, Kepler. Some features are named for counterpa rts on Earth-bays and gulfs; capes and la kes. NAMES O N THE MOON

The Moon's far side-the 4 1 per cent never seen b y observers from Earth-was a n unknown landscape until photographed b y a Russian spacecraft i n 1 959. Photogra phs showed a cratered land­ scape lacking the large "seas" observed on the lunar surface that faces Earth. Since 1 959, photog raphs and direct observations by U.S. astronauts, along with instru­ ment read ings, have provided m uch detailed information. RECE N T DISCOVER IES

61

L u n a r Apen n i n es ( l eft) : Here is part of a splendid ran ge, up to 1 4,000 feet h i g h , which runs 450 miles a r o u n d the west side of M a re I m b r i u m . Big crater i s Archi medes, 70 mi les wide. (Lick Obs.) Four l u n a r features (right): The crater P l ato, 60 m i l e s wide, d o m i n ates the sce n e . �xte n d i n g to the left a n d a bove P lato a re the Alps. To Pl ato's r i g h t, near the edge of the p hoto, is the Stra i g h t R a n g e , a c h a i n of a d o z e n peaks stretc h i n g 45 mi les. Above a n d s l i g htly to the right of P l a to, the mountain Pice towers 8,000 ft. a bove Mare I m b r i u m . CLick Obs.J

Tycho ( l eft) : T h i s is a mountain-ri n ged p l a i n like Copernicus, with width of 54 m i les. The rays extend h u n d reds of mi les. (Yerkes Obs.) Pickering (right): A meteoro i d a p p roac h i n g from the l eft struck the l u n a r s u rface at a s h a r p a n g le, making a crater and strew i n g i m pact d e b ris, v i s i b l e a s " rays" exte n d i n g towa rd the right.

The Moon h a s a r i g i d rock c r u st s om e 6 2 0 m i l e s t h i c k ,

cove r i n g a r e l a t i v e l y s o f t i n t e r i o r . The r o c k i s m a i n l y basa l t a n d a n o r t h o s i t e , f o r m e d by c oo l i n g of m o l t e n m a t e r i a l s .

S a m p l e s d a ted b y rad i oa c t i v i t y a r e a s o l d a s 4 . 4 b i l l i o n

yea r s ( t h e s o l a r system i s a b o u t 4 . 6 b i l l i o n yea r s o l d ) . The maria a r e s o l i d i f i e d l ava flows, s o m e resu l t i n g f r o m c o l l i ­

s i o n s o f t h e M o o n w i t h b i g meteoro i d s l o n g a g o . Mony craters o re vo l c a n i c ; others res u l t from meteo r o i d i m pac t s . I m pacts p r o ba b l y a r e respo n s i b l e a l so for the " r a ys , " wh i c h c o n s i st of fra g m e n ted r o c k exten d i ng o u t f r o m c r a ­ t e r s l i ke s p r a y . N u m e r o u s s c a r p s a n d " r i l l s " (va l l ey- l i ke depre s s i o n s ) r e s u l t from fau l t i n g . Recent d i scove r i e s m a k e the Moon m o r e , n o t l e s s , i n ter­ est i n g for a m a t e u r o b server s .

Meteo r o i d i m pac t s a r e

w a t c h e d f o r . A l p h o n s u s a n d o t h e r c r a t e r s a re i n spected regu l a r l y for s i g n s of red d e n i n g o r h a z e t h a t wou l d i n d i ­ cate v o l c a n i c a ct i v i ty. Observers check the i r o b s e r va t i o n s a g a i n s t m a p s a n d photog r a p h s to detect r e c e n t c h a n g e s on t h e l u na r s u r fa c e . Occ u l t a t i o n s a n d ec l i ps e s a r e v i ewed . P e r h a p s most of a l l , the a m a t e u r c a n sti l l e n j o y the face of the Moo n , w i t h the p l a y of s u n l i g h t on i t s sto r k fea t u r e s , a s o n e of t h e wo r l d 's g r a ndest specta c l e s . O n c e i n o w h i l e , a t fu l l p h a s e , t h e Moon

ECLIPSES

passes through E a r t h 's s h a d ow, a n d we have o n e of na­ tu re's

m o st

g lorious

phenomena :

an

ec l i pse .

In

any

TOTAL LU N A R E C L I P SE S, 1 9 8 5 - 2 000 1 985 May

4

1 989 Feb. 20

1 992 Dec .

9

1 996 S e p .

1 985 0ct . 28

1 989 Aug . 1 6

1 993 J u n .

4

1 997 Mar. 24

2

1 993 N ov. 29

1 997 Sep . 1 6

1 994 May 25

1 999 J u l .

1 99 1 Dec . 2 1

1 995 Apr. 1 5

2000 J o n . 2 1

1 992 J u n . 1 5

1 996 Apr.

2000 J u l .

1 986 Apr. 24

1 990 Feb.

9

1 98 6 0ct. 1 7

1 990 Aug .

6

1 987 0ct.

7

1 988 Aug . 2 7

4

28 16

63

Lunar eclipse: H e re, the S u n ' s

light comes f r o m the left. T h e M o o n is eclipsed a s it enters Earth's shadow. This is not completely d a rk, beca use some sunlight is refracted i nto it by Earth's atmosphere. Since red rays penetrate the atmos­ phere most easily, the Moo n's disk looks red d ish.

one yea r there may be two or even th ree lunar eclipses, or none. A tota l lunar eclipse lasts as m uch as 1 hour and 40 min utes-much longer than a tota l so lar eclipse. There is plenty of time to see it and observe the ever­ changing colors. During an ecli pse, familiar lunar fea­ tures ta ke on a new appearance. I n a tota l solar eclipse, the disk of the Sun is com­ pletely hidden by the Moon. But in a lunar eclipse, the disk of the Moon can often be seen, even i n Earth's shadow. Some of the sunlight passi ng throug h Earth's atmosphere is refracted so that it fa lls on the Moon, giving it a coppery h ue.

Occultation: J upiter and satellites

appea r afte r bein g occu lted by the Moon . The sharpness of J upi­ ter's image when the planet is just at the edge of the Moon in­ d icates that the Moon lacks an appreciable atmosphere.

64

OCCU LTATIONS Now and then the Moon passes i n front of a star or planet, h iding i t briefly. This event, called an occultation, is of g reat interest to map ma kers . I f the instants o f disappearance a n d rea ppearance ore accurately timed by observers at different locations on Earth, the data can be used to determine the exact dis­ tances between those locations. Exact positions of many geographical points have been checked i n this way. Many experienced observers do occultation work. A small telescope, a short-wave radio, and a good watch or stopwatch are the essentia ls. Accurate time signals can be obtained from Radio Station WWV. Dates when occu ltations will occur can be found in Sky and Telescope magazine.

( 1 ) Observe occultations. (2) Make detai led drawi ngs of Moon's surface. (3) Observe ecli pses. (4) Watch sunrise over the l u nar mountains. (5) Watch the ever-chang ing appearance of severa l particular lunar features, night after nig ht. (6) Take photog ra phs (see page 1 32). (7) Time the Moon's risi ng and setting times, over a lunar month. (8) Study the rays. (9) Watch for im pacts. (1 0) Watch Alphonsus and the area nea r Aris­ tarchus for sig ns of volcanic activity. T H I N GS TO DO

The Face of the Sun: Sunspots appea r on the solar d isk (picture i n cen ter). At lower r i g h t a group o f sun spots is compared f o r size with Earth. At the upper left are several prominences-g igantic tong ues of incan descent gases projected outward from the S u n ' s su rface.

The Sun The Sun, like other sta rs, i s a giant sphere o f in­ ca ndescent gases. Its diameter is a bout 864,000 mi les­ over 1 00 times Ea rth's. It is the Sun's g ravitational at­ traction, mostly, that governs the motions of planets. The Sun is so large that if Earth were at its center, the Moon wo uld orbit a bout halfway between Earth and the Sun's surface. Earth revolves around the Sun in a path that is an e l lipse, not a perfect circle. Hence our distance from the Sun changes slig htly from month to month, being greatest in J u ly (94.4 m i l lion mi les), and least in J a n ua ry (9 1 .4 mi llion). SUN-GAZ I N G

66

Ca ution! Protect your eyes!

Ma ny telescopes come equi pped with specia l fi lters, eyepieces, or prisms for use in direct observation of the S u n . Some telescopes a re fitted with an adjustable screen so that the Sun's image ca n be projected . If you r telescope has no such p rotective devices, they ca n be made or bought. Gen era l ly it is better to buy the specia l eyepieces, prisms, or fi lters than to ta ke a chance on homemade devices. The sun ca p , which is a fi lter mounted in an adapter to fit over the eyepiece, can be used with 2 Y2- to 3-inch telescopes. For larger i nstru m ents, special eyepieces desig ned for the pu rpose a re necessa ry. Some observers usi ng large i n stru ments red uce the aperture by fitti ng a cap over the objective. T h e ca p consists of a snug-fitti ng cardboard disk with a hole of the size desired cut i n the center. But cutting down the aperture a lso reduces defi n ition in sma l l detai ls, and it does not prevent the eyepiece from getti ng h ot. Do not observe through balsam or g e latin fi lters. These ca n m e lt, and eye damage ca n ha ppen q uickly. High power is not req ui red to see s u n spots-60x to 1 OOx is usua l ly sufficient. Bi noculars (use fi lters over the objectives!) wi l l reveal the larger spots. Proving the Sun's rotatio n : These ph otos, taken at two-day i n terva ls, show a p p a rent movement of s u n spots across so l a r disk. (Yerkes Obs.)

67

The safest way to observe the Sun is to project its image onto a screen held i n back of the eyepiece. A simple device, easily made, i s shown on this page . It a l l ows several person s to observe at the same time. Don't try to set the telescope on the Sun by looking through the finder or by gazing up the tube. That is risky and awkward. If you a re using a screen , a i m the tube by watc h i ng its shadow on the screen . If no screen is being used, hold a card u p behind the eyepiece . For observing without optica l aid, welder's glass # 1 2 is safe; exposed film and smoked g lass are not . Refractor and reflector equipped for solar observation: The Sun's image is p rojected harmlessly onto a light screen. This is moved to a position that gives an image of the size desired. Focusi n g is done with the eyepiece. Observers MUST NOT look through either finder or eye· piece except with a solar filter of the proper density.

Sunspot cycle: Rapid in­ crease in spots occu rs, then a slaw decline. The time from peak to peak is about n years.

"' i-----+--.--+---+-4-+----l

; "' i----f-'H-----t-\t----1--il----+"'1 •

Lr---f- --11't--f---t-T---1r---t-\-- +---l i The best tim e to look at the Sun is in the morning, before its full heating effect is felt. Then the atmosphere is steadier. vary from specks to giants 90,000 mi les across. The largest can be seen without optical aid. These odd features, disturbances of great violence, are often referred to as "storms." Each has a dark core, or umbra, and a n outer gray band, the penumbra . Bein g cooler t h a n t h e surrounding surface, t h e spots appear darker. Changing in size and position daily, some disappea r after a day o r two, while others can be observed crossing the solar disk, taking a bout 14 days for the journey. This apparent crossing is due to the Sun's rotatio n . T h e num ber o f spots varies from j ust a few i n a year to as many as 1 50 in one day. They come in cycles, the period between maximums being a bout 11 years. Sun­ spot n u m bers a re given in several publications, i n cluding Sky and Telescope. Through a telescope the Sun's surface has a g ranular or mottled a ppearance. Near sunspots, and particu larly toward the edge of the disk, whitish patches ca lled "feculae" may be seen. Other phenomena thot can be seen at times are flares, which a re bright flashes near the spots. These a re rare but worth lookin g for.

S UNSPOTS

69

Total ecli pse (l eft) : When the Moon is n e a r e n o u g h to Earth so that its a p p a rent size is g reate � than the S u n ' s, the l u n o r d isk can com p l etely hide the solar disk. Then the wide, shimmering co rona c a n be see n . Annular eclipse ( right) : W h e n Moon i s n e a r its maxim u m d ista n ce from Earth, its apparent size is sma l ler than S u n 's. Hence a ring (a n n u l us) of S u n remains visibl e, a n d S u n ' s coro n a cannot be see n .

I n creasing n u m bers o f sunspots are closely a l lied to i n creasing a u rora l displays, and genera lly there is i nterference with radio and television . W h e n ever you observe increased a ctivity on the Sun, or notice u n usua l i nterferen ce with radio a n d TV, watch for a u rora l dis­ p lays a day or so later. have a lways excited m a n ki n d . Super­ stitio n has clothed them with stra nge a n d terrifyi ng mea nings. Science has looked forwa rd to ecli pses a s occasions w h e n certa in solar phenomena, s u c h as p romi­ nences a n d the corona, which a re ordi n a ri ly invisi ble, ca n be observed. Today the u nsuperstitious o bserver looks forwa rd to an eclipse eagerly, and so does the professio n a l astronomer, a lthough h e ca n use the coro­ nagra p h to produce an a rtifi cia l eclipse in the observe-

SOLA R ECLI PSES

70

tory. Natu re's own display remains u n riva led i n splendor. A tota l so lar eclipse occurs when the Moon i s directly i n line betwee n Ea rth and S u n . If it is not exactly i n line, on ly a parti a l eclipse occu rs. An annular eclipse hap­ pens when the Moon, though directly i n l i n e with Earth and Sun, is fa r enough away from Earth so that th e dark centra l pa rt of its shadow ca n not reach Earth. There a re at least two tota l ecli pses a yea r, a n d sometimes as many as five, b u t few people h a v e a cha nce to see them. The paths a long which eclipses ca n be seen a re narrow, a n d tota lity ca n last o n ly a bout 7% min utes at most. Among the features of a tota l eclipse are the so-ca l led Bai ly's Beads. These a re seen j ust as the Moon's black disk covers the last thin crescent of the Sun. Sun light shining between the mounta i n s at the Moon's edge looks like spa rkling beads. The Dia m o n d Ring effect is a fleeti ng flash of light i m m ediately preceding or fol lowi ng tota lity. At the time of tota lity, the observer with a sma l l tele­ scope ca n see the Su n's p rominences-long, fl amelike tongues of i n ca n d escent gases, a ppeari n g a round the Sola r eclipses: M a p s h o w s paths traced by Moo n ' s s h adow d u ri n g ec l i pses, 1 979-2006.

edge of the Moon's disk. Also d uring tota lity we see the glorious fl lmy corona, its g lowi ng gases stretching out m i l lions of mi les from the blacked-out Sun. To get the m ost out of the few minutes of a n eclipse, preparations m ust be made long in advance. Decide what you want to do and get ready. Prepare equipment carefu l ly. Study the charts that appear i n newspapers and other publications to determine the path of the Moon's shadow. Try to pick a good location near the area where the eclipse will last the longest, and a long the center of the shadow's path. A lso, if possi ble, flnd a spot at a high elevation so that you ca n get an uninterrupted view to the horizon, in the direction of the path of the shadow. Some o bserv­ ers must travel thousa nds of mi les to view a tota l eclipse, because the shadow path is only a bout 1 00 mi les wide.

PREPAR I N G FOR A N ECLIPSE

Drama of Sun and Moo n : As o solar ecli pse nears totality, the l ast c rescent of S u n d isappears. Sunlight at the rugged edge of the l u n a r d i s k forms Boily's B e a d s (left) and Diamond Ring effect ( m i d d l e ) . With tota lity, the spectacular corona appears. Tota lity seldom l asts more tha n a m i nute or two. Ra rely, it lasts as long as about 7 Y2 m i n utes.

Stages of a solar eclipse: This striking series of exposu res plan ned a n d

made b y a news p hotographer suggests possibil ities f o r other camera­ minded observe rs. (Roy E. Swan, Minneapolis Star)

Prior to tota lity, the on rush of the Moon's shadow can be seen. Have a white sheet on the g round, and just as tota lity begins, try to observe on it the so-ca l led shadow bands-light and dark ba nds o n ly a few inches across and a few feet apart. Last but not least, look for stars in the sky during tota lity, and look for Mercury. Notice the shadows and sunlight fi lteri ng through the trees d uring the progress of the eclipse. O bserve the effect of darkness on birds a nd anima ls. Carry a ther­ mometer and watch the temperature. And by a l l means use your camera ! 73

Sky

Colors

As s u n light passes through Ea rth's atmosphere, the rays of different colors-bl ue, yel low, red-a re scattered and a bsorbed by the air to various deg rees. The sky is blue beca use b lue rays scatter more than the others. Notice how the cha n g i n g density and com position of o u r atmosphere-how smoke, dust, a n d other p a rticles-make colorful sun rises a n d sunsets. See how the atmosphere, by scatteri n g light, gives us twi light. J u st after sunset or before s u n rise, watch for the "sun p i l l a r"-a b ri l lia nt col u m n of light of the sa me color as the sunset or s u n rise, risi ng a bove the S u n . Of a l l s k y color effects, the best k n o w n a re rai nbows. These a re p roduced as rays of s u n light strike droplets of water in the air. The droplets a ct as prisms, dispersin g t h e l i g h t a n d separati ng t h e colors. Rain bows appear opposite the S u n . Seen from the g round, a rain bow is a lways less than half a circle. The length of the bow depends upon the S un's a ngle. 74

Seen from an a i rplane, ra i nbows often are complete cir­ cles. A s i n g l e ra i n bow has red on the outside, violet i nside; but occasiona l ly a second bow forms outside the first, with its colors reversed . Rarely, as many as five bows are see n . Sometimes a round , g l owing spot is seen o n each s i d e of the S u n . These mock suns, or "sun dogs , " are a l ways associated with a halo around the S u n . The h a l o , usua l l y 22° i n rad i u s , i s due to refraction o f sunl ight b y ice parti­ cles h igh i n the atmosphere (see p . 56) . The aurora borealis (northern lig hts) i n the northern hemisphere a n d aurora australis (southern lights) i n the southern hemisphere a re produced i n Earth's atmosphere by i m pacts of charged particles from outer space - some of them from sunspots . Auroras are most freq uent i n the higher latitudes, but have been seen as far from the north pole as Mexico and as far from the south pole as Austra l i a and N ew Zea land . L o o k toward t h e p o l e of you r h e m i ­ sphere . Often auroras a r e m ore spectacular after m i d ­ n i g h t . N o speci a l equ i pment i s req u i red - just a l ertness . But auroras a re good subjects for the camera (see pages 1 30- 1 3 1 ) .

Zodiacal light: T h i s fa i n t glow n e a r the horizon, a l o n g the ecli ptic, may be s u n l ig h t reflected from meteoric materi a l . look for it j u st after twi· light i n the west, and before dawn i n the east.

Auroras often look like thin patches of distant fog. Many persons have seen auroras without recognizing them. Look twice at any fog like g low seen toward the pole. Rea l clouds hide stars; auroras do not. Watch for any change i n a hazy g low near the horizo n . It may become a n a rc, then break up into rays like search light beams, then q uickly disappear. Auroras come in many forms and colors-red and g reen most freq uently. Particularly impressive a re the irregu la r vibrating or pulsating bands or a rcs, a lso ca lled draperies. The auroras ca l led flames may reach high overhead like gigantic windblown ribbons. Another spectacular form is the corona, or "crown," formed by rays that seem to radiate from a point nea r the zenith . Zodiaca l light and Gegenschein are phenomena of the night sky that are not commonly recognized. They a re appa rently light reflected from minute particles­ perhaps meteoroids-in the band of the Zodiac. The Curtain a u rora : No pointing or photograph ca n fully rep resent the g h ostly, consta ntly shifti ng pattern of this grand natural spectacle.

Rays

Rayed a rc

Rayed arc

Glow

Flames

Types of Auroras

Rayed arc

Zodiaca l light is a hazy band rising from the h orizon a long the ecliptic just after twilight in the west, or just before dawn in the east. The Gegenschein, or "counterglow," is a brightening of zodiaca l light at a point on the ecliptic opposite the Sun. Sometimes the Gegenschein is seen when the zodiaca l light is invisible. Look for it a bout midnight and toward the south, nea r your meridian. 77

Relative sizes of planets as seen from Earth : When i n best positi o n s for observation, Ven u s, J u piter, a n d Satu rn a re large but shrouded i n

The Planets and Asteroids Every observer should become fa miliar with t h e constella­ tions of the Zodiac (page 25). Except for asteroids (pla netoids, or minor planets), the pla nets genera l ly fol low the Zodiac. When we see in the Zodiac a "star" that is not accounted for on a star chart, it is quite sure to be a planet-particularly if it doesn't twi n k le. Planets shine with a steady light. I n the telescope, they are sma l l disks, not mere points of light like stars. They va ry in size, appea ra nce and apparent motion. All revolve about the Sun and shine by reflecti ng sun light. Mercury and Ven us fol low orbits nearer to the Sun than Earth's. They are ca l led the inner, or inferior, pla nets. All other planets have orbits outside Earth's, and 78

clouds. V e n u s a n d Mercury in fu l l p h a se show but s l i g h t deta i l . U r a n u s a n d Neptu n e are m e r e dots. O n ly M a r s shows a l a n d sca pe.

they a re genera l ly ca l led the outer, or superior, p l a n ets. At times a superior pla net appears to have a retro­ grade motion. In moving through a conste l lation , it seems to slow down a n d then go i nto reverse. After a few months the forward motion may be resumed. Actua l ly, p l a n ets do not "reverse." The a ppearance of reversi ng is d u e to c hanges i n relative positions of Ea rth a n d p' l anets as they move in their orbits. Mercu ry a n d Venus a re the true morn i n g a n d eve n i n g "sta rs," beca use they stay near t h e S u n . O n ly j ust be­ fore s u n rise and j ust after sunset, a few ti mes a yea r, can Merc u ry be see n . Venus is visi ble for longer periods, and someti mes in daylight. Mars, J upiter, and Saturn may be ca l l ed morning or evening sta rs when they domi nate the sky in early morning or eve n i n g . 79

The relative positions of most stars remain the same for decades. But planet positions are changing constantly, and thus a re not shown on star charts. To tlnd a planet, one must use a special ta ble or list, as on page 92. To locate Ven us, Mars, Jupiter, or Saturn o n a certain date, you need to know only the name of the conste l la­ tion in which to look. These p lanets ordinari ly are brig ht enough to be distinguished easily from the nearby stars. But the outer planets-Ura nus, Neptune, and Pluto-are fainter and harder to distinguish. More exact informa­ tion a bout their positions is available in astronomical publications (see pages 1 46- 1 47). Uranus and Neptune can be spotted in binoculars, if one knows exactly where to look. But only a 1 2-inch telescope or better ca n pick up an object as faint as Pluto.

LOCATING PLANETS

TO LOOK Superior planets are seen best when in opposition; that is, when Earth is directly be­ tween the p lanet and the Sun. Then the planet is c losest

W H EN

Opposition : S u perior planet i n

l i n e ( o r nearly so) with Earth a n d S u n , Earth bei n g i n middle. Quadrature: Superior p l anet at

right angles to Earth-S u n l i ne. Conjunction : Superior planet on

Earth-Sun line, beyond S u n . Greatest

elongation: I nferior planet at right a n g les to Earth­ Sun line. I nferior conjunction: I nferior p lanet d i rectly between Earth and Sun. Superior

conjunction : I n ferior planet on Earth-Sun line, beyond Sun.

80

Apparitions of Venus: Photos taken over a two-month period show changes in the p l a n ­ e t ' s a p p a rent s i z e a n d i t s attitude. Apparent size varies as d istance from Ea rth changes. (Han s Pfleumer)

to Earth and we see its l i ghted side ful ly. Mercury a nd Venus, the i nferior planets, are never i n opposition . We see the i r l i g hted faces fully only when the Sun is between them and Earth; then their disks are q uite sma l l . They appear brightest and largest at the time of greatest elongation, when the planet and the S u n , as seen by us, are at their g reatest distance apart - as much a s 48° for Venus a nd 28° for Mercury. Then we see only part of the planet's lighted side. The best time to observe p l a nets is on moon less n ig hts, or when they a re opposite i n the sky from the Moon , a n d when they a re hig h above the horizo n . Atmospheric conditions i n ­ fluence seeing ( p a g e 2 9 ) . A t or near fu l l Moon , observing is poor for both planets and sta rs. O B S E R VI N G E QUIPM E N T De­ ta i l ed study of planets requ i res large, spec ia l , and expensive equipment; but one can see and do much with a sma l l telescope. Cer­ tai n features can be observed with

binocula rs, such as the fou r large moons of J u piter. With very powerfu l binocu lars the phases of Ven u s and ri ngs of Saturn are discerni ble. For rea l planeta ry work use a 3- to 1 2-inch refractor or a 6- to 1 8-inch reflector. Most reflecting telescopes operate at f/6 or fiB­ that is, the foca l length of the primary m i rror is 6 to 8 times the m irror's diameter. But the best telescopes for observi ng the planets a re of long focus, a bout f / 1 2 -the ratio of many refractors. The long focus cuts down the fi e ld of view but i ncreases magnification . Experi ment with your eq uipment to determi n e the magnification that wi l l g ive the best results. M E RC U RY, nearest to the Sun, is a n airl ess rock ball scorched to 800 ° F. on the day side, frozen to - 280 ° F. on the night side. Spacecraft photos show a mou ntainous, cratered surface. Mercury is usually h idden in the Sun's g l a re, but severa l times a yea r, near elongation, Mercury is visibl e just after sunset or before sunrise. Mag n itude va ries from - 1 .9 to + 1 . 1 . Times of visibility a re indi­ cated in a l ma nacs, so metimes i n newspa pers. Ma ny people have n ever seen Mercu ry, but it. is easy to see if one looks at the rig ht time in the rig h t place. Like the Moon, Mercury goes th rough phases that a re visible in a sma l l telescope. Some astronomers claim to Phases of an Inferior P lanet

Sun

An I nferior P la n et as "Morning Sta r" and as "Eveni n g Sta r" (positions as viewed from above)

have seen vague permanent markings on the surface. I nteresti n g to watch i s a passage of Merc u ry a cross the Sun's disk-the phen omenon known as a "transit." It occurs a bout 1 3 times i n 1 00 years. Mercury looks like a sma l l black ba l l ro l ling slowly across the S u n . The n ext tra nsits wil l be on Nov. 1 3, 1 986, and N ov. 6, 1 993. (CAUTI O N : Protect the eyes! See pages 66-67.) nearly a twi n of Ea rth in size, a lso goes through phases. At its brig htest, a bout magnitude -4 (it varies from - 4.4 to 3.3), it will be a thin crescent i n your telescope. At its faintest, the entire disk i s lighted . This peculiarity is d u e to the fact that the thin crescent phase occurs when Venus is nea rest Earth, a n d the full phase when it is fa rthest away. The brightest planet, Ven us is at times visib le i n day­ light. Observe in early even ing or just before daw n . Few markings can be seen t h rough a telescope; the pla net is a l­ ways s h rouded i n dense hot clouds of ca rbon dioxide. Spacecraft p hotos show a rocky, probably vol c a n i c ter­ rai n . Venus tra n sits the Sun rarely. The last tra nsit was in 1 882; the n ext wi l l be i n 2004. VENUS,

-

83

Seasons on Mars: As a pola r ca p s h r i n k s with the com i n g of s u m m e r, the b rownish a re a s tu rn g rayish­ g re e n . Each pol a r cap shows a full cycl e of w a x i n g a n d waning d u ri n g the Martian year.

The red color of Mars and its brightness (mag­ nitude - 2.8 to + 1 .6) make it easy to recognize. It has excited the imagi nation more than any other planet, a n d some causes of a l l the controversy ca n be seen with a sma l l telescope when Mars is near oppositio n . To g l i m pse even the la rgest featu res, at l east a 6-inch re­ f lector or a 3-inch refractor is needed. Either should reveal the white po l a r caps rathe r disti nctly; a l so, g rayish -to-green and reddish areas between the poles. The pol a r caps (now known to be water ice) widen a n d shri n k according t o the Ma rtian seasons. The northern cap wi l l extend ha lfway to the equator d u ring wi nter in the north ern hemisphere, fhen shrink fa r back i n summer. The southern polar cap varies s i m i l a r ly. The g rayish a n d g reenish a reas, but n o t t h e reddish ones, also s h o w sea­ son a l changes. Occasionally a l a rge portion of Ma rs is obscured by a g iant dust storm .

MARS

Rotation of Mars: The red planet's day is 24h 37 m - s l ig htly longer than Earth's. Accord i ngly , a Ma rtian feature needs a little over 1 2 h o u rs for its apparent motion from one side of the disk to the other.

c

{

�O 1 ;6

M e r ury

days

1 0.9

Approximate diameter of d isk: seconds of arc**

yellowt

- 3 .3

+ 1.1 -

-

redt

+ 1 .6

to

- 2.8

-

- 4.4

- 1 .9

to

0 0

1 1

0 0

0 0

to

16

2

1

22h

1 0" 1 4m

yellowt

yel lowt

to + 0.9

- 1 .4

green

+ 5. 7

0 0

2 5 - 0.4

5

17

3.8

yrs. yrs.

yrs.

1 8. 5

yrs.

1 64 . 8

84.0

29.46

yellow

+ 7.6

0 0

2

2.5

23h

247.7

3 1 ,000

32 ,000

75 , 1 00

yellow

+ 14

0 0

days

6.4

2 ,500

to 4,700

2,9 1 0

1 ,960

2,670

39.44 3,664

Pluto

1 ,028

2,677

30.058 2,793.50

Neptune

to

1 ,606

1 9. 1 82 1 ,782.80

Uranus

to

to

744

9.539 886. 1 4

Saturn

to

- 2. 5

4 4

45.3

1 7.9

-

9•som

0

60.8

days

23hS6m

244.0

yrs.

24h 37m

days

days

1 1 . 86

687.0

days

88,700

4,2 1 8

7,927 365 .3

7,526

224.7

600

248

-

1 61

0

oranget

{

to

to

-

367

35

-

to

5 . 203 483.32

Jupiter

25

1 . 524 1 4 1.54

Mars

92.90

1 .000*

Earth

0.723 67.20

Venus

tColors observed by unaided eye. *Astronomical unit = 92,897,000 m iles (mean distance to Earth from Sun). **Approximate mean diameter of Sun = 3 1 ' 59". Approxi mate mean diameter of Moon = 31 '05".

Color

Magnitude range

No. of moons Visible in : 3-inch tel. 6-inch tel .

3,025

{ 88.0 days { 58.65

Diameter: m iles

Period of revolution: Earth = 1 yr. Period of rotation: Earth = 1 day

Distance from Ea rth: mil lion miles

astronomical units* 0.387 million m i les 3 5.96

Mea n distance from Sun:

I I 1 ..- .- .. _ ,. ,.. .. . ..,

In the past, some observers cla imed to have seen "canals" on Mars, perhaps made by i ntel ligent beings. But the planet is so indistinct and tiny even in a large telescope ( 1 / 1 0 inc h in diameter at the focus of a 40-inch refractor!) that proof was impossible. Spacecraft photo­ graphs today show no ca na ls-just rugged, rock-strewn l a n d with im pact craters, volca nic cones, d u n e a reas, a n d ca nyons cut by streams i n the remote past, before m ost of the planet's su rface went dry. No evidence of higher forms of l ife is visible. Mars often is observed through fi lters. With a red filter the polar caps are not so brig ht, a n d the dark areas are da rker. The opposite effect is apparent when a green or blue fi lter is used. When Mars is i n a favorable position, consta n t obser­ vation is exciti ng. Use a bout 200X with a 3-inch refractor, or higher power with a 6-inch reflector. ASTER O I D S a re small planets with orbits mostly be­ tween those of Mars and J upiter. Some travel withi n

86

., . ... ... ,,...

The face of Mars: As the planet

rotates, different featu res come into view. Many can be seen by the amateu r u n der good co ndi. lions. Map exaggerates featu res at top and bottom.

the orbit of Mars and come nearer Earth than any large planets . E ros comes Arcodia as near as 1 3 . 5 m i l l i o n •re loreum Scandia m i les, as it did i n 1 975 a n d will again i n 20 1 2 . More than 3 , 000 asteroids have been identified , but most of them are very sma l l and faint. To locate even the big ones, we must know exactly where to look. S i nce asteroids are not confi ned to the zod iacal pathway, amateurs often m i stake them for novas (pages 1 1 4- 1 1 5) . The position o f a n a steroid, however, w i l l b e seen to change over a period of a few evenings, while the posi ­ tion of a nova remains the sam e . Asteroids r a n g e from a few m i l es to m o r e t h a n 600 m i les i n d i ameter. Radar images i n d i cate Nov. 27, 1990 48,000,000 i rreg u l a r shapes, but no features a re visible even Diacria

..

Oppositions

of

Mars:

About every two yea rs, Ea rth is between S u n a n d Mars. Then observi n g i s best. D i a g r a m (from U . S . Nava l O bse rvato ry data) sh ows o p p o s i t i o n s f r o m 1 978 t o 1 999, with Ea rth­ Mars d istances in miles.

Feb. 1 2, 1 995 62,800,000

Feb. 23, 1 980 63,000,000

Mar. 1 7, 1 997 61 ,300,000

Sep. 28, 1 988 36,500.000

Dance of the moons: J upiter's four larg­ est satellites make changing patte rns as they circle the planet. Except when hidden by the planet, all four can be see n with binocu lars. They were discovered i n 1 61 0 by Galilee, who was the first to use a telescope for astronomical observi ng.

through telescopes . Fou r - Ceres, P a l l a s , J u n o , and Vesta - are l isted in the Astronomical A lmanac, which g ives for each the right ascension and declination, d i sta nce from Earth, merid ian transit time, and approximate magnitude for every day i n the year. The positions of E ros are given only for ti mes when it is most favorably situated for ob­ servin g , for it is only 25 m i les in diameter. To l ocate an astero i d , look up its position i n the A lmanac a n d check this position i n your atlas with respect to easily identified nearby sta rs. Then use telescope or b i noculars . Ceres, the largest asteroid (diameter 623 m i l es), was the first to be d i scovered . Pallas (378 m i les) was the next, then J u no ( 1 53 m i les), and then Vesta (334 m i les) . Bright­ ness depends on size, distance from Sun and from Earth, and angle of reflection of the sun light. the largest planet, is a ba l l of hydroge n , with some hel i u m , ammonia, and traces of other gases . I t may have no hard surface - just a shell of frozen gases thick­ e n i ng toward the relatively sma l l core, probably roc k . W i t h a magnitude o f about - 2 . 5 t o about - 1 . 4 , J upiter is one of the sky's brig htest objects . I t has 1 6 sate l l i tes, four of which, at a magnitude of a bout 6, are conspicuous in a small telescope and can be seen with bi noculars. Two J U PI T E R ,

e -

e -

satell ites requ i re a 1 2- i nch telescope; ten, a very l a rge instrument. In 1 979, photographs taken by Voyager spacecraft revea led a ring of dustlike particles a round the equator. The four brig htest sate l l i tes, named l o , E uropa , Gan­ ymede, and C a l l i sto, were d iscovered by Ga l i l e o . Their chang i ng relative positions are published annually i n the A lmanac and other sources (pages 1 46- 1 47). One interesting sight is the shadow of a sate l l ite crossing the planet's d i s k . Another i s the cloud - l i ke structures, or "bands, " across the middle of the disk . These show changes in color and extent. Among them , and visible in a small telescope, i s the so-ca lled Red Spot - sti ll unexplai ned . Ecli pses and occultations of the J ovian sate l l i tes make good observing . I n fact, when the pla net is well placed for observation, it is a rare night when some i n terest i ng phe­ nomenon cannot be witnessed . J u p i ter is one of the most satisfying of a l l objects for small telescope s . second-largest planet, is a ba l l of frozen hydro­ gen, methane, and ammon i a , probably with a rocky core . Its magnitude varies from a bout - 0 . 4 to + 0 . 9 . When it is near opposition, its steady yellow l ight makes it a com­ mand i ng object i n the sky, and it vies with J u piter i n beauty

SAT U R N ,

Tran sit of satellite across Jupiter's disk: In fi rst two stages, both sate l lite (sm a l l white object) e n d i t s s h a d ow can be see n . I n other stages sate l l ite i s i n v i s i b l e .

89

and i nterest . The rings a re one of the most specta cular celestial sights. Saturn is wel l endowed with moons - seventeen . like J u p i ter's larger moons, Saturn's bea r personal na mes . Within the range of med ium-size telescopes a re Titan (the largest), Iapetus, Rhea , Tethys, and Dione. These sate l l i tes are not as active as J upiter's . Tita n , magnitude 8, can be seen easily in sma l l telescopes . Saturn's famous ring system consists of sma ll bits of ice. It can be seen with a telescope as small as a 1 V2- i nch, with relatively low power. For a rea l l y good view, a t least a 2 V2- to 4 - i nch refractor or a 6-inch reflector should be used . With a good telescope and high power, the appa rent solid band is seen to be divided i nto two rings sepa rated by a dark line. This l i ne, discovered by J . D. Cass i n i i n 1 675 , is called Cassi n i 's D ivisi o n . I n l a rge telescopes sti l l another d ivision h a s been seen i n t h e outer ring . Over the yea rs we see first one side of the ri ngs, then the other, as the planet's tilt with respect to our l i ne of sight changes (see page 91 ). At times the rings are edge-on and d ifficult to see, as was true i n 1 980. The complete cycle repeats after about 291/2 years.

The rin ged planet: The a rtist has p a i nted deta i l s af Satu r n t h a t can b e seen w i t h small telescopes. O n e may see also the shadow of the g lobe fa l l ­ i n g across t h e r i n g s . Deta i l d e m a n d s g o o d see i n g a n d gaod optics.

Attitudes of Satu rn: The a n g le of o u r l i n e of sight to the p l a net changes accord i n g to a 29'12-year cycle. (E. C. 5/ipher, Lowell Obs.)

U RAN U S , the third-largest planet, is a nother ba ll of frozen hydrogen , methane, and a m m o n i a , p r o b a b l y with a rock core . I t is s o far from the Sun that its year equa ls 84 of ours . Its mag­ nitude i s a bout + 6; hence it can be seen i n binoculars and, if seeing is good , with unaided eyes . N one of its five major moons or surface features i s visible in a sma l l telescope. I n 1 977-78 eight or n i ne evenly spaced rings were detected by a irborne o b s e r va t i o n s of o c c u l t a ­ tions o f sta rs. To locate U ranus, plot its coord i nates (from your Al­ manac) on a star chart. With high power, U ranus is a very sma l l , pa le greenish d i s k . Its steady light d i stinguishes it from a star. N E PTU N E , sim ila r to U ranus but slig htly sma ller, is much farther from the Sun . Its annua l journey takes a bout 1 65 Earth years. With a magnitude of about + 8 , it can be seen with good binoculars, but to spot it we must know its exact position (check the A lmanac) .

91

PLANET LOCATIONS, 1 985- 1 990 positions of Mercur Uranus, N ne, and Pluto, refer to Astronomical Almanac or ot!.r astronamica handbooks , or to Sky ond Telescope ""'''!' Z ine. Asterisk •J indicates morning star. Dashes indicate Planet is loa near Sun for obMrvotion. (Source, Solor and Plonetary Longitudes, by Stahlman ond Gingerich. ) For

M

JANUARY

�

�

APRIL

JULY

OCTOBER

* Taurus Lea

•teo Libra Virgo • teo

Cancer *Taurus

Scorpius

VENUS 1 985 1 986 1 987 1 988

Aquarius Aries •Aquarius Taurus

1 989 1 990

• tibra Capricornus Aquarius •Ophiuchus Co�icornus

1 985 1 986

Aquarius •ubra

1 987

Pisces

Taurus

1 988

•tibra Scorpius Pisces •Q!!!i! uchus

*Capricomus

1 989 1 990 1 985 1 986 1 987 1 988 1 989 1 990 1 985 1 986 1 987 1 988 1 989 1 990

Capricornus Aquarius Pisces Aries Taurus Gemini * Libra •Scorpius •Ophiuchus * Sagittarius

*Aquarius MARS Aries •Sagittarius

Taurus

*Ca�icomus

JUPITER

•Copricornus *Aquarius Aries Taurus

Gemini SATURN *Libra •Ophiuchus •Ophiuchus *Sagittarius *Sagittarius * Sagittarius

T h e d i scovery of N e p t u n e , in

*Taurus *Taurus

• Sagittarius Gemini Cancer *Pisces

•tea Sagittarius Capricornus *Virgo Pisces

Cancer *Pisces

*Taurus

*Capricornus *Pisces *Pisces *Taurus *Taurus

Copricornus Aquarius *Pisces *Taurus *Gemini *Cancer

Libra Scorpius Ophiuchus Sagittarius Sagittarius *Sagittarius

1 846,

Libra Scorpius Ophiuchus Sagittarius Sagittarius �ittarius

w a s a tri u m p h

f o r m a t h e m a ti c a l a stro n o m y . I t s presence i n a certa i n a rea o f t h e sky w a s p redi cted before i t w a s a ctua l ly dis­ covered. Since t h a t t i m e it h a s tra v e l e d o n ly a little more th a n h a lfway a ro u n d t h e S u n . Its two moons ca n

92

21' _ _ _

1 9'

2ft

I I

1 I 1- - - - - - - - - I

_j

I

e lji

-� - - I - JI

I

SAGITTARIUS

I

•w

SCUTUM

L

I 1

1 8'_ 0" 1

e'( j__

_ _ _

•

x'

- 30"

Path s of U ra n u s , 1 985- 1 995, and Nept u n e , 1 985-2000 1 9"

- - - --1

SAGITTARIUS

SCUTUM

I I

:_ - - •.:::. I

1 8h

_

1 7'

�·

1 6'- 1 0"

- 30"

b e seen only i n very l a rge telescopes . T h i s pla net presents noth ing of interest to the sky observer except the fun of hunting for i t . PLU TO , t h e p la net fa rthest from t h e S u n , i s the most recently di scovered . Dr. Perciva l lowe l l , of lowel l Observ­ atory at Flagstaff, Arizona , made the calculations, and a young astronomer named C l yde Tombaugh discovered the planet i n 1 930 by comparing photog raphs of the same area of sky taken at different times. It i s a very fa int o bject - 1 4th magnitude - and a 1 2 - i nch telescope may be requi red to see i t . The smal lest planet, it has one moon .

93

Comet's path through solar system: The orbit of a comet i s a l o n g loop. The comet's tail genera l l y poi nts away f r o m the S u n . The nearer the comet is to the Sun, the more the tail trails out across the heavens.

Comets The most mysterious mem bers of the solar system a re the comets. They a re not reg ular visitors i n the night sky, like planets; but they do visit us frequently-as many a s five or more in a yea r. They usua lly a ppea r sudden ly, stay i n view for a few weeks, then disappear. Some return after a period of yea rs, but most do not. The fi rst person to report a new comet is honored by having his name given to it. No wonder a mateurs spend so much ti m e seeki n g th ese el usive objects! One of the most stri king comets of many yea rs was the eig hth comet discovered i n 1 956. The discoverers were Arend and Ro land. This was one of the few com ets to exhibit a tai l both fore a n d aft. It beca m e so bright that it cou ld be seen with the u naided eye despite city lights, cha l lenging everyon e to look at it. But very few comets become bright enough to be seen without binoculars or a telescope. 94

Comets a re apparently planet-sized m e m bers of our so lar system, but of u ncertai n origi n . They shine by re­ flecting sunlig ht, as planets do; and they g low as sunlight ion izes gases i n them. Besides gases, they conta i n enormous concentration s o f larger particles, perhaps meteoritic materi a l . Some comets have no tai l at all, but i n others it is spectacular i n form a n d length. The tai l a p­ pears to be made of materia l thrown off from the head. Comets may appear i n any part o f the s k y at a n y ti me o f year. M a n y a n ob­ server sea rches for comets every clear night. By sca n n i n g a differen t z o n e e a c h evening, h e ca n cover m u ch o f the sky during a week. looki ng for n ew comets or for the return of old ones is good sport. Many observi n g g roups divide up the patrol work. Bi nocu lars ca n be used, but a 3- to 6-i nch telescope is better. Use low power for a wide field. O n ce a comet is found, a camera attached to the POI NTERS F O R OBSERVERS

Comet Mrkos: T h i s n e w comet a p p e a red i n 1 957. The series of photos was made over a span of several days. (Mt. Wilson and Palomar Obs.)

telescope will be usefu l . Because fil m can store up light, m uch more of a comet ca n be seen on a photograph than through the telescope . For long exposure, fol l ow the comet (p. 1 32 ) . Si nce comets change positions against the back­ g round of stars, stars i n the photograph will tra i l . A comet ca n b e superb i n a small telescope . Usually it i s a fa int, g lowing object with a hazy ta i l s o t h i n that stars shine through it undimmed . I n the head the concentrated pa rt is the nucleus; the hazy material a round it, the coma . The n ucleus may be 1 00 to 50, 000 m i les in d i a meter; the head , 30, 000 to over 1 , 000, 000 m i les across . The ta i l , if a ny, inay spread widely and stretch out 1 00 m i l l i o n miles. I t usua lly points away from the S u n , because of pressure of light and the solar wind . Ta ils change in a ppearance d a ily; changes can be sketched o r photographed . P E R I O D I C COMETS Some comets travel i n e l l i ptical or­ bits and, after a period of time, retur n aga i n . (Most comets do not . ) Most famous of the "repeaters" is H a l ley's comet , observed closely i n 1 682 by Edmund H a l l ey, the Engl ish astronomer. He d iscovered that its orbit was e l l i ptical and . pred icted it would return i n 1 758 (it d i d ) . I t w a s seen many times before Halley's day, perhaps as early as 2 3 9 B . C . Its a ppearance i n A . D . 1 066 is depicted i n the fa m o u s B a ye u x t a pestry, which chronicles the Nor­ man conquest of E ngland by William the Conqueror. H a l ley's Camet, May 29, 1910: Its many reg u l a r a p pearances h ave made it the best known of a l l comets. (Yerkes Obs.)

SOME REAPPEAR I N G COMETS Dote

1 985 1 986 1 986 1 987 1 987 1 988 1 989

Name

(Sep)

Giacobini-Zinner

(Jon)

Boethin

(Mm)

Halley

(Aug)

Encke

(Dec)

Borrelly

(Sep)

Temple

(Sep)

Brorsen-Metcolf

2

Discovered

1 900 1 975 - 239 1 786 1 904 1 873 1 847

Dote

1 989 (Nov) 1 990 (Moy) 1 990 (Sep)

1 990 (Oct) 1 990 (Dec) 1 99 1 (Nov)

Nome Lovas Schwassmonn -Wachmonn 3 Honda-MrkosPoidusakovo Encke Kearns-Kwee Foye

Discovered

1 980 1 930

1 948

1 786 1 963 1 843

(Courtesy Brion Marsden)

Comets may be bright during one visit, fa int the next, and after many visits may va nish for good , perhaps d i s i n ­ tegrating to become meteor showers. Si nce a return cannot be accurately pred i cted , star t hunting a month i n advance . Consu lt a l manacs and handbooks {pp. 1 46-7) . ( l ) Observe a zone for comets regu­ larly. (2) Check l i sts of recurring comets and watch for them . (3) P l ot the course of a comet on your atlas . (4) Try to pred ict the d a i l y positions of a comet. (5) Make d raw­ i ngs or photographs of changes i n appea rance. THINGS TO DO

Comet anatomy: A sketch m a d e d u ring observati o n s by the Comet Re· corder of Association of l u n a r and Planeta ry Observe rs. (David Meisel)

97

End of

a

bolide: A meteor breaks

up

with a fl a re and a b a n g .

Meteo rs D u ring every clea r nig ht, need le- like strea ks of light a re seen cutti n g across the sky. One, two-a dozen or more­ may be seen in an hour. Often ca l led "shootin g stars," the objects that m a ke these trails a re a ctu a l ly bits of stone a n d i ron from outer space, ca l led m eteors or meteoroids. They race into our atmosphere with such speed-up to 44 mi les per second-that friction with the air heats them to i n ca ndescence. Most turn to vapor a n d dust long before they reach the g rou n d . U n usually s low, b r i g h t meteors are ca l led "fireba l ls." Frequently their tra i l remains visib l e for some time. Fireba l ls that explode a re "bolides." Most meteors a re no bigger than rice g rains, and they become i n ca ndescent 50 to 75 miles u p . larger ones brea k u p d u ri n g their fiery trip th rough our atmosphere, and fra g m e nts of th ese hit the Ea rth . O n ce in few cen­ turies a rea l ly big one hits, such as the m eteor that made Meteor Crater in Arizona. 98

Some m eteor trails a re short, a n d som e a re long-20° or more. Most a re white, bl ue, or yellow. Fireba l l s a n d bolides a re very bright. T h e i r strea k is thicker, lacking the usual thin, needle-like a ppeara n ce. Sometimes thei r path is crooked or broken, a n d several explosions may mark their course. Meteoritic materia l enteri ng Earth 's atmosphere daily may total severa l tons. The num ber of m eteors actu a l ly reaching the ground may be in the bil lions, but these are so sma l l that their tota l weight is estimated at only one ton . Fra g ments of meteors fou n d on the ground are ca lled "meteorites." They usua lly have peculiar sha pes and a re h eavy for their size. Most consist m a i n ly of iron, som e a re p redomina ntly stone, a n d sti l l others consist o f both . Coba lt a n d n ickel, too, may be present. Meteorites look fused, or melted, on the outside. Hence they a re easily confused with bits of slag. O bserv­ ers who want to be able to identify m eteorites should study specim e n s on display i n planeta ri u m s and museums. Usua l ly m o re meteors are seen near midnight a n d i n early morning, be­ cause then our p a rt of

Intruder a mong the sta rs: A bril­ l i a n t meteor was caught on this 40-m i n ute exposu re of the C assio­ peia region. A clock d rive kept the camera tra i n ed o n the sta r field . (Walter Pa/mstorfer, Petten­ bach, Oberosterreich, A u stria)

99

Iron meteorite: This specimen, about 8 i nches long, weighs 33 pounds. Hollows i n its su rface were left by portions removed by· frictio n and heating d u ri n g passage throug h atmosphere. (American Mus. of Nat. Hist.)

Ea rth is facing forwa rd in our journey around the Sun and we a re heading into the meteor swarms. I n g roup observing for meteors, each person has his own section of the sky to patrol. Binoculars a re not necessary but help; wide-field ones a re best. Meteor trails make i nteresting photogra phs (see page 1 0 1 ). Also, amateurs with a short-wave radio re­ ceiver can "listen" to meteors. The set is tuned to a very weak dista nt station, prefera bly a bove 1 5 megacycles. The volume is kept very low. When a meteor in the upper atmosphere ionizes a patch of air, creati ng a momentary "reflector" for sig na ls, the volume of the station's signal rises sharply. Doppler changes i n pitch may occur. On a good morning, severa l h undred meteors may be heard. I n certain pa rts of the sky, over periods of days or weeks, "showers" of m eteors can be seen. In an hour 1 50 may be observed. Showers occur whenever Earth, i n its journey around the Sun, encoun­ ters a vast swarm of meteors-perhaps remains of a comet. A shower appears to radiate from one point in the sky, and is likely to recur there a bout the sa me time METEOR S HOWERS

1 00

each year. Showers are named after the constellations from which they seem to radiate. ( 1 ) Observe showers, a lone or with g roups. (2) Count meteors seen in a n hour. If a shower, count the n u m ber per min ute. (3) On a star chart, plot points of beginning and end of meteor trails. (4) If a meteor fa lls in your vicinity, try to flnd it. Watch your loca l newspaper for report. Find persons who saw the meteor fa l l and attempt to trace it. Cooperate with a nearby observatory, if a ny. T H I NGS TO DO

PROMINENT

METEOR

SHOWERS

Listed here are a few prominent "trustworthy" showers. Many more are l isted in textbooks and hand books. Approx. Approx. Date Name

Constellation (Max.)

Lyrids........

Lyra

Perseids . . . .

Perseus

Orion ids...

Orion

Leonids.....

Leo

Apr. 2 1

Aug. 1 1

Oct. 1 9

Nov. 1 5

Approx.

D uration

No. per

(days)

Hour

4 25 14 7

Radiant Point

1 8 h04m + 33 ° 3 hoom + 57° 6 hosm + 1 5° 1 0hoom + 22°

8 70 20 20

Giacobinid meteor s ho w e r , 1 946: I n this time exposure, a rotating shutter i n the camera broke up the meteor trails but not the star trails. I n d rawing af same field, meteor trails are extended to the radiant point. (Peter M. Millman)

,q•

1

•

�

0v-cO •

:

::;:;,;�: -::;;;( -\

.....

" G

.- -

//�,•'Y

-'r AO' r---."1:-+-,-;;o;-:

e"

Dec

RA

•

ll

'i>

Omega Centauri: This splendid globular cluster, visib le to u naided eyes, g litters in the southern constellation Centaurus. I t r01sembles the northern hemisphere's g reat M 1 3 cluster i n Hercules. (Harvard Obs.)

Stars The ga laxies-the millions of isla nd u niverses in space­ are made up of stars, planets and sma ller bodies, gas, and dust. All the sta rs are spheres of g lowing gas; many are millions of mi les in diameter. Some are 1 0,000 times as thin as Earth's air at sea level, and some are so dense that a cupful of their substa nce would weig h tons on Earth. Star interiors have temperatures measured in millions of degrees, and at their surfaces temperatures up to 55,000° F . are com mon. Proba bly ma ny, if not most, sta rs a re ringed by planets. All stars visible in sma l l telescopes a re within our own ga laxy. The nea rest one to Earth is 4% light years away -26 tril lion mi les. Even this nea rest star, Proxima Cen­ ta uri, is so dista nt that in the greatest telescopes it is a mere point of light. 1 02

Sta rs differ in brightness, color, a n d size. U n like the planets, they shine by thei r own light. Yea r after yea r they mainta i n almost exactly the sa m e relative positions. I n a n cient times people n oticed that the sta rs seemed to form fi g u res. legends of kings a nd q ueens, of h unters a n d stra nge a n i m a ls, were told a bout them. During the thousands of years since, star patterns have changed somewhat, but the n a mes linger. Even the p rofessional astronomer uses a p p roximately the old group outlines and calls them by the old n a m es­ Cepheus the King, Cassiopeia the Queen, a n d Draco the Dragon. I n the southern hemisphere, too, w here star groups were n a m ed much later by seafarers, the old names sti l l h o ld. Scientifi ca l ly, constel lation s have no sig nifica nce ex­ cept as names of a rbitrarily outlined pa rts of the celesti a l sphere. Practi ca l ly t h e y a re the ABC's o f observin g . O n ly when the observer knows the main constel lations of his latitude ca n h e find his way around the sky. All the constellations are mapped o n pages 1 48- 1 57. The maps t h e re i n d icate the seasons when the con­ stellation s a re conveniently visible. To fi n d the map on which a conste llation ap­ pears, look u p the constel­ lation in the i n d ex. CONSTELLAT I O N S

Double cluster in Perseus: This open agg regation of stars is fa· mous. "C rosses" o n brighter stars are due to optical effects i n the telescope. (Lick Obs.)

MYRIAD SUNS Pick out any sma ll group of stars. look at them with the naked eye, then through binoculars, and then through a telescope with an objective of 3 inch es or more. You notice an almost u n believable in­ crease i n the number of stars that a re visible, and the stars look different, too. A star that to the eye looks single may appear double or even quadruple in the T H I 2 5 I R I G H T I S T STA R S * telescope. A small hazy "....... ... ....... .. ... _ ,.... , .., 57) patch may turn out to be a c luster of h u ndreds of Mat"'" .....,.,.. stars. Certain stars, if .._ ..... ,...,, watched from night to 9 a Conlo Malorfs Sirius -u 98 night, show changes in Conopus a Carinae -0.7 (Alpha a Contourl brightness; these a re ca lled Centourl) 4� 0.0 36 -0.1 Ardurus .. loll.. variables. Stars that ap­ v26 a Lyo.o 45 Capello +0.1 pea r and vanish are novas, « Aurlgae 900 +0.1 p Orlonlo ..... or "new stars." 11 ,._ +oA a Conls MI-ls The richest star fields 1 11 AcheTnor +0.5 a Erlclonl (lleta are in the Milky Way. On p C.ntouri 490 Centouri) +0.6 a clear, dark night, far 520 letelgeuM +oA a Orlonls 16 Altoir +o.e Aqulloe from city lights, parts of 61 Aldebaran +0.9 a Tourl (Alpha a Crvcls the Mi l ky Way look like 370 +0.79 Cruds) clouds. This seeming con­ 520 +o.9 Ante­ .. Scorpll 220 +0.9 .. Vlrglollo Spica centration of stars is due 23 ·-lhaut + 1 .2 .. Plods A-"" to perspective. Our gal­ 35 + 1 .2 PoRea p 0..'-""' axy, some 80,000 light 1 600 + 1 .3 Deneb .. c.,. nl {J Crvcls (lleto yea rs in d i a m eter, i s + 1 .3 Crvcls) +u .. Leonlo ... . ... shaped like a double con­ + 1 .5 Aclharo • Conls vex lens, thi n at the edges Majorls 45 +2.0 Costor .. O..lnor­ and thicker toward the :no + 1 .6 Shaulo A Scorpll 470 + 1 .6 lellatrla y Orlonls middle. Our solar system is a bout 30,000 light years *Fr- rhe OINetftr'• Handlooolr, Royal ,.._ "-lcol Society of Conocla, r-to. from the center. When the a

1 04

Albireo in binoculars: The object

Albireo in a telescope: Now the

appears as a single sta r (the large one near center of field).

star appears as a double. Magni­ fication has red uced the field .

observer on Ea rth looks toward the Milky Way h e is looking th rough the ga laxy towa rd a n edge. Poi nt your telescope or binoculars to any part of the Milky Way, particularly the neigh borhood of Sagittarius, toward the center of our ga laxy. The stars a nywhere present a colorful picture, from blue-white Vega and Sirius to yellow Capella and red Arcturus and Antares. See how many colors you ca n detect. Some double stars are particula rly interesting because of the contrast i n their colors-for exa mp le, Albireo ( {3 Cygni), one o f the fi nest doubles. In star atlases many variable stars and clusters a re m a rked . These a re worth fi n d i n g , a n d many a re fo u n d

easi ly. For certain variabl e stars, detai led charts a re Epsilon Lyrae in binoculars: The sta r appears as a n o rd i n a ry dou­ ble (nea r center) i n a starry field .

Epsilon Lyrae in a telescope: At

1 OOx with good seeing, the dou­ ble becomes a pai r of doubles.

1 05

SOME

Canrtel/atian A n d romeda Aquarius lootes Cancer Can .. Venaticl Capricorn us Ca ul o pe i a Cenfaurus Corona Borealis Crux Cygnus Delphinus Draco Draco Eridanus Gemini Hercules Lyro Lyra Lyro Orion Orion Per1eu1 Scorplus Tria n g u l u m Tucana U r o o Major Ursa Minor Virgo

Star y

r •

'

a a', ola

r

a

ll y

, "'

32 a a • ' • • •

p

I In M42 ,

a

& or 6

p r a

y

DOUILI

I NTEREST I N G Magnitudes

3.0, 5.0 4.4, 4.6 3.0, 6.3 4.4, 6.5 3.2. 5.7 4.0, 3.8 4.2, 7. 1 , 8 . 1 0.3, 1 .7 4. 1 , 5.0 1 . .ol, 1 .9 3.0, 5.3 ...0, 5.0 4.6, 4.6 4.0, 5.2 4.0, 6.0 2.7, 3.7 3.0, 6 . 1 4,6, 4.9 4.6, 6.3 4.9, 5.2 1 .0, 8.0 4.0, 1 0.3 2.5, 6.3 4.0, 8.5 1 .2, 6.5 5.0, 6.4 4.5, 4.5 2 . .ol, 4.0 2.5, 8.8 3.6, 3.7

Dirtance Apart (sec.)

10 3 3 30 20 376 2, 7 ..

6 5 35 10 62

31

7 5 4 201 3

2 9

STARS

C ol ors

28 3 4 26 14 19 6

ItA.

Dec

02"00" 22"26'" 1 4"43'" 01"44'" 1 2"54'" 20" 1 5'" yellow, yel low yellow, bl ue, blue 02"25'" 1 4"37'" yellow, red 1 5"38'" white, b l u e 1 2"24'" blue, b l u e 1 9"29'" yellow, blue 20"44'" yell ow, grHn 1 7"3 1 '" white, white 1 7"43'" yell ow, p u r p l e 03"52'" yell ow, blue 07"3 1 '" white, white 1 7" 1 ,ora nge, g reen 1 8"43'" yel l ow, blue 1 8"43'" yel l ow 1 r43• blue 05" 1 2'" blue, blue

+ 42 . 1 - 00.3 + 21.3 + 29.0 + 38.6 - 1 2.7:' + 67.2 - 60.6 + 36.81 - 63.8' + 27.8' + 1 6.0' + 55.2' + 72.2' - 03. 1 ' + 32.0' + 1 4.4' + 39.6' + 39.6' + 39.6' - 01.2'

05"36'" 02"47'" 1 6"26'" 02"1 0'"

- 02.6' + 55.7' - 26.3 ' + 30. 1 ' - 63.2' + 55.2' + 89.0' - 01 .2'

yellow, blue wh ile, white ora nge, grMn yellow, blue blue, bl ue

(Quadru ple)

l'uillan ( 1 950)

blues yell ow, b l u e red, wh ite yellow, b l u e blue, white white, white yel l ow, b l u e white, yell-

oo"29'"

1 3"22'" 0 1 "49'" 1 2"39'"

1

needed, or sets of coordi nates so that you can plot these stars in your atlas. Detai led lists of sta rs with their characteristics and positions a re g iven i n textbooks, astronomica l h a ndbooks, and other publications (see pages 1 46- 1 47) . In many sta r atlases, certa i n objects a re la beled "M," with a n u m ber fol lowing. The M refers to the list of clusters a n d nebu las prepa red by the o ld-ti me French astronomer Charles Messier. The list includes a bout 1 00 i nteresting objects visible i n s m a l l telescopes. If your 1 06

atlas does not show them, refer to a list of Messier objects and plot them in your atlas. Then see how many you ca n locate. Binocu lars wil l help you to view sta rs and clusters, but the sma l l aperture and low power are severely limiting. A 3- to 6-i nch refractor, or a 6- to 1 2-inch reflector, is far better. An eq uatorial with setting circles is best, because when properly oriented it ca n be trained on fai nt objects easi ly. The so-ca lled rich­ field telescope, with its short focus and very wide field, provides fine views of clusters and nebulas. The best tim e to observe is when the atmosphere is sti ll a n d clear, and when the ti me of the month is be­ tween the Moon's last quarter and first quarter. O bserve double stars when the seeing is especial ly good; that is, when the stars look like steady points of light a nd do not twi nkle much. All stars are best observed when well a bove the horizon. When at the telescope, keep both eyes open, to relieve strain. learn to make the most of a q uick g lance. If the observing eye tires, close it now and then to rest it, a n d then open it at the eyepiece. When using a refrac­ tor, observe with the dew cap on. This helps to keep out extra neous light and darkens the

OBSERV I N G TIPS

Why A l g o l w i n k s : W h e n one

of its two com ponents passes in front of the other, the light dims. The cycle takes 2 34 d ays.

background. Fainter objects ca n then be seen better. A faint o bject that is stared at may seem to become fai nter. The reason is eye fatigue. Look a little to the side of the object, and it wil l be brighter and clearer. Most of the stars ca l led "multiple" are either double, triple, or q uadruple. Good eyes can make out the famous double at the bend i n the handle of the Big Dipper. The brighter of the two is Mizar; its com pa n ion is A lcor. They revolve a bout a common cen­ ter. I n a telescope, Mizar itself can be seen as a double. Epsilon (e ) Lyrae can be seen with the unaided eye as a very close double nea r the limit of visibility. It is easi ly "split" with a pair of binoculars. Each of the two stars can be split again with a sma l l telescope of good quality at 1 00 to 200X. Epsilon Lyrae is a q uadruple star, or "double double." Polaris (North Star) and Castor (a Geminorum) a re doubles. Each can be split with a 3-inch. Besides being beautiful to look at, double stars can be used to test the optics of your instrument (see page 1 7). MU LTIPLE STARS

are groups of stars that travel together through space. Mem bers of "open" clusters a re widely separated and can be resolved easily i n sma l l tele­ scopes. In "g lobular" clusters the sta rs a re closely crowded toward the center and are difficult to resolve in a sma l l telescope; the c luster is just a little hazy spot. Many clusters a re a treat to see. They g lint and sparkle like sprays, i n a way no photograph could suggest. The Pleiades ("Seven Sisters") form what might be cal led a visua l open c luster. Six of them are easy for the unaided eye. I n a sma l l telescope the cluster shows

STAR C L U STERS

1 08

hundreds of stars, and in a large telescope these appear enveloped i n clouds of lumi­ nous gas; The Hyades a re another fine, wide c luster. Best of a l l is the Double Cluster in Perseus. Some c lusters very faint to the eye magica l ly turn into thousa nds of stars when the telescope is trained on them . Look at M 1 3-one o f the best. To the eye a lone it looks like a hazy star. In binocu lars it is a little round cloud. But i n a 4-inch telescope you begi n to resolve the stars. This g lob­ ular may have 1 00,000! Contrast M 1 3 with M44, a beautiful open cluster. In this our large telescopes can de­ tect a bout 400 stars. The light output of many a star varies. Some stars show a regular variation i n a few hours, some over a period of many days, and others over several years. VARIABLE STARS

The effect of exposure: Photos of

Hercules cluster, M 1 3, were made with exposures of 6, 1 5, 37, and 95 minutes (top to bottom) with 60-i nch reflector. (Mt. Wilson)

M M••l•r'• lllt c........ Awlgo

A ••• •A M O U I ITA I C L U itlll

NOC-Do.,er'• New 0--' c...lotw

...... ( ,,., lA

Dec

,...

06iecf .. MS7

� + su• Oil'.. + 32.6·

.....

.,.,.. + 20.2•

Opeoo

1 3"..... + 21.6·

ow..w

c..lllpela c-.-

M103 NOC 3766 • 489

01"3G"' + .0.4° 1 1 .,.. _ , 1 .3.

c:..t..rw er.

NOC 4155

1 3"2.. - ,g.o• 1 2"51· - .0.1 °

• .U01 MS9

OloWar Open

. ... + .,tO

MU

06'o6'" + 2«"

Opeoo

.-... c:-

c:- v.....w

c,.. .. o-111 1

M3

.,

..._...

M13

16'..- + 36.6·

._.. .......

75 M15

22"1r + ..,... 2 1 "21'" + 1 2.G0

,_ ,_ ........ ...... ....... ......

,_

,....... ..

Allllrala

,_

NOC I69

.... ... MN M23 M6 M7

Ml 1

M45

NOC .OU

• A3N NOC 1 CN • 61 1

Open Open

Opeoo

Open

Open ow..w

Open ow..w

02'1r +56.,. o,.. 02'W' + G.IJ" Open

1 7',.. - 1 t.o• Opeoo 17'37"' - U,tO Open 17'51. -u.a• Open 1 1".. -06.3· Opeoo o3"U" + 24.0" Open 1 tw" -.o.6· Opeoo

IMI2P - 72A· ow..w

...... ....

....,.,, ..,_,... l= ..... er.cr.r. .... .,.. ......,

'YIIIIIe to .,.

..

....

6-1

Oollll leW with � .... .. ..... .... . ...

Spill lar, ....._ Ill ti l c.laof.l ...... .... (.... ..., ... .., ..... l .... ....... a

_ .... .. .. "GNat Cluller",

o-lleW

.... .

l ::::. ......, .... ... .. ....

., ... ...... ...., ...... .. ari .... ........, ... ......: . ......, ... ... .., ...... .. .,. ..... ......, ...... .. .,. .....

u,g y_.., ...... ..

.,..

Many are irregular; they have no defi nite period of variation. Regular varia ble stars differ in the amount they va ry and i n the lengths of their periods, but thei r behavior is fairly predictable. Irregular variables a re unpredictable. They may remain at the same brightness for long periods of time before they begin to vary; or they are continually varying. The short-period regular variables a re of two kinds­ eclipsing and pulsating. The best exam ple of an eclipsing variable is Algol ({3 Persei), for its variation can be ob1 10

served without optical aid. This star is actua l ly a double, with two mem bers revolving a bout a com mon center. The variation occurs as one member passes in front of the other-thus cutting off part of its light-at regular in­ terva ls. With Algol the eclipse occurs in a bout 4 hours, at interva ls of a bout 2% days. At maxi m u m Algol is at a bout 2.2 magnitude, and at minimum a bout 3.5. Pu lsating varia bles are sin g le sta rs that contract and expa nd at reg ular interva ls. Their light output increases and decreases accordingly. Omicron Ceti (Mira), one of the most fa mous of vari­ ables, rises from a faint 1 Oth magnitude to 3d (at times even 2nd) in a bout 1 50 days. It takes a bout 1 80 days to fade again to minimum. Beca use of this g reat ra nge in brightness it has been mista ken for a nova . Beehive (Praesepe) cluster: This open star group (M44), a fine show in binoculars, is located about 14 ° southeast of Pol lux. (Yerkes Obs.)

AAVSO cha rt: The observer estimates the brightness of the variable sta r Omicron Ceti (smal l dot i n uying the device, determine whether it can be used without any modification of your telescope. MU LTI P L E EYEPI ECES,

for specific purposes are offered usua l ly under the names of their i nventors, such as Kell­ ner, Ramsden, and Abbe. The Kellner is recommended for wide fields with accurate color and images good to the edges. The Ramsden is used by many for planetary observin g . The Abbe orthoscopic eyepiece is favored by observers who m ust wear their g lasses at the telescope. The image is formed farther out from the eyepiece. The Abbe gives a large, highly corrected field. The Barlow lens, designed to be used with regular eyepieces, can be adjusted so as to m u ltiply the magni­ fying power of any eyepiece by as much as three. It re­ duces the field of view, and does not raise the limit of useful magnification as determined by the objective. Zoom eyepieces have but limited usefulness.

SPECIAL EYE P I ECES

"stop" certai n colors and a l low others to come through . Certain details ca n be d istinguished only if a color fi lter is used to i ncrease the contrasts. Fi lters transmit the color of the fi lter; thus, a red fi lter transmits red, and other colors such as g reen or blue appear dark. Since fi lters a bsorb some of the light, they

COLOR FI LTERS

1 39

What a filter does: M a rs as seen without a fi lter (a bove) a n d through a red filter.

may be used to cut down g lare, such as Moon glare or the g lare of the sky when you a re observing Ven us i n daylight. Red, green, and blue fi lters a re contrast fi lters. A solar eyepiece has a very dense g lass fi lter fitted to the cap of the eyepiece. For planets, colored optica l g lass fi lters can be pu rchased from optica l goods supply stores. Or you ca n make fi lters out of Wratten gelatin fi lter sheets. To make a fi lter, unscrew the cap of an eyepiece and cut a piece of the gelatin sheet to fit it. Then screw the cover back on the eyepiece, just tight enough to hold firm ly but not so tight as to wrinkle the fi lter. Gelatin fi lters are perfectly safe with Moon, p lanets, and sta rs. Do NOT use them when looki ng at the Sun th roug h a telescope (see page 67). For the Moon, neutra l fi lters cut down g lare. Pola rizing fi lters, or Pola roid, reduce i ntensity of backgrou nd light when you a re observing in daylig ht. For planets, use red, g reen, and blue fi lters. For Jupiter and Venus i n daytime, use Wratten K2 or Polar­ oid to reduce sky light intensity. Some sky observers treat themselves to an extra telescope. The owner of a long­ focus instrument, used for p lanet study, gets himself a A SECO N D TE LESCOPE

1 40

short-focus "rich-field" for viewing broad star fields. Another observer's 8-inch reflector is too big to take on vacations; so he acquires a 50 mm. refractor. The wou ld-be satellite tracker or meteor watcher whose genera l-purpose 6-inch reflector provides a field of 2 ° o r less brings home a wide-field portable tracki ng scope. Two telescopes of widely differing types mean variety in observing. They a lso facilitate group observing. Many amateurs have made their own observatories, with peaked or flat roofs that can be removed, opened, or slid out of the way. Some even have domes. An observatory saves time a n d energy that ordi narily go into carrying a n i nstrument a round and set­ ting it up. A shelter gives p rotection from the wind, and ma kes a convenient place for storing books, maps, and equipment. Astronomical magazines give plans.

THE OBSERVATORY

All equipment should be i nspected frequently. Reflectors req uire q u ite frequent checking of the collimation (a lignment) of the diag­ onal m irror or prism with the objective and eye­ piece. Improper a lignment causes distortion. Alignment is poor if the objective lens or mirror is E Q U I PMENT I NSPECTIONS

Backyard observatory: T h e rota!·

able dome, 8 feet wide, houses a 4-i nch refractor. Observatories are usually u n heated, because warmi ng would ca use a i r turbu­ lence. (Gordon W. Smith)

Field of

Finder improperly a l igned: Sta r is centered in the eyepi ece but not i n the find er. The fi n d e r s h o u l d be a d j u sted so t h a t the object is centered in both.

not set exactly at right angles to the tube; or if the eyepiece is out of line; or, i n reflectors, if the sec­ ondary mirror needs ad­ justment. Scratches on the surfaces of objective or eyepieces a lso can blur i mages. A fi nder should be checked often. Improper adjust­ ment makes it hard to sight the telescope when high powers are used and the field of view is, therefore, small. There should be no p lay in the telescope mounting. When moved to the desired position, the tube should stay there without any springing back. If springing oc­ curs, check the counterweight adjustment. If the optica l surfaces of a telescope a re good, if everything is a ligned, and if seeing is favorable, even bright stars wi l l appear as sma l l, neat dots of light. In a refractor, around these dots you may see one or two faint concentric rings of light, ca l led diffraction rings. These are normal in a n instrument of good qua lity. eyepiece

If a telescope is taken from a warm house out i nto the cold, it may perform poorly for 1 5 min utes o r more-until it becomes adjusted to the tem­ perature change. The same is true if the instrument is taken from a cold place to a warm one. Some observers arrange a safe place for the telescope in an unheated garage or barn. I n winter, don't try to observe from a warm room with

STORAGE H I N TS

1 42

the telescope pointed out the window. Mixing of cold and warm air currents wil l make the images boil. After observing, the open end of the tube of a re­ flector should be covered with a bag or cap for protec­ tion against d ust. (Protectors can be made with card­ board, chamois, or p lastic.) A refractor should be simi­ larly protected. If the reflector is open at the mirror end, this shou ld be covered, or the mirror itself capped. If you ta ke a telescope from cold air into a warm room, don't cover it u nti l any dew that has formed on the lens or mirror has disappeared. Otherwise spotti ng of the optical surfaces may occur. Do not try to remove the moisture with a cloth . Wait until it has evaporated; then remove dust with a camel's-hair brush. Make a box in which the telescope tube ca n be snugly stored. Remove the eyepiece before storing. Keep eye­ pieces in a sepa rate, padded, dustproof box. Remember that jolting tends to put optica l parts out of line, espe­ cially in reflectors. CORRECT I N G

Good alignment

ALIGN­

Misa lign ment is the most com mon ai lment of reflectors, but well-made o n e s h a v e a d j usta b l e parts, so a lignment ca n be corrected. In a Newtonian reflector (the most common MENT

Alignment of optical system: A

good i nstrument properly a ligned shows stars and planets as neat points or d isks (left). Poor align· ment causes ragged or distorted images ( right).

Poor alignment

1 43

type), take measurements to see that the diagona l mirror or prism is centered in the tube. Next, look into the tube from the open end. The diagona l should be centered against its en larged reflection in the mirror; if not, adjust mirror. Final ly, look straight through the eyepiece-holder opening at the diagona l. If its reflection is not centered, adjust diagona l (see drawings below). Cleaning of lenses and mirrors must be done properly. A tiny piece of grit on cloth or paper used for wipi ng the lens or mirror may leave scratches that permanently impair performance. Never rub a lens or mirror; never touch the optica l sur­ face with your fi ngers. Remove dirt by dusting with a camel's-hair brush . If further cleaning is needed, the lens or mirror can be dabbed (not rubbed !) gently with a mild soap-and-water solution, then rinsed thoroughly i n clear water and a l lowed t o dry in the air. Eyepieces should not be imm ersed . They a re p recisely assem bled and should not be ta ken apart except by a person who knows how. For instructions on cleaning eye­ pieces and objectives, consult books on te lescopes. CLEA N I N G OPTICAL S U RFACES

Align ment of ob jective in a New­ tonian reflector: Both the diag­ o n a l a n d its reflection m u st be centered when viewed th rough open e n d of the tu be. ,_ align....,.

Good

alignmont

Distance of diagonal from objec­ tive in a reflector: Reflection should be centered as seen throug h eyepiece-ho l d e r opening with eye close to holder.

lightly d ust optica l pa rts frequently. Beyond that, freq uent cleaning can be as bad as none at a l l . lenses and mirrors that are subjected to no more than normal dust, dewing, and chemical action of the atmosphere may need cleaning only once a year. Remem ber: slight soi ling is not so bad as scratched g lass or a badly worn mirror coati ng due to excessive zea l a bout cleaning. Eventual ly the mirror of a reflector wi l l need recoating. Si lver coati ngs may last as little as six months; aluminum coatings may do for many years. The coating of mirrors is a job strictly for the pro­ fessionals who advertise i n astronomical magazines. When your telescope is in use, be sure that all parts move easi ly. If any part works hard, never try to force it. Find out what is wrong before using it any further. Hint: check clamps in right ascension and declination. Some moving parts may req uire lu brication. This should be done with the freq uency and kind of lubricant recommended by the man ufacturer. Most refractors come equipped with a dew cap that fits tightly over the objective. Use it while observi ng. It helps to keep dew from forming on the lens. If a dew cap is not i ncluded i n your equipment, you can make one out of a card boa rd tube. Paint the i n side black-a flat black. Make sure of a tight fit, a n d let the tube extend beyond the objective a bout 6 to 9 inches. Proper care and maintenance wi l l add to the life of equipment a n d vastly i ncrease the p leasure it gives you. If you want to make your own reflecting telescope, check relia ble magazines or books (pages 1 46- 1 47) for suitable designs. Such a p roject wi l l tax your ski l l and your patience, but it can be very rewarding. OTHER MA I NT E N A N C E

1 45

Incidental Information S o m e Amate u r O bserv i n g G ro u ps American Association of Va riable Sta r Observers (AAVSO), 1 87 Concord Ave. , Cambridge, MA 0 2 1 38. Worldwide; largest group of amateurs doing ser i ous wor k . Members' observations of variable stars ore processed and made available to astronomers throughout the worl d . Other divisions: sunspots; photoelectric photometry. American Meteor Society (AMS), Dept. af Physics and Astronomy, State U niv. , Geneseo, NY 1 4454 . Stresses visual and telescopic observations of meteors. Association of Lunar and Planetary Observers (ALPO), Box 3AZ, U n iver­ sity Park, NM 88003 . Informal i nternational group studies Moon, planets, etc. Section recorders supervise systematic work . Royal Astronomical Society of New Zealand (RASNZ), % Carter Observ­ atory, P. O . Box 2909, Welli ngton C. 1 , N. Z . Sections do variable-star observing, telescope making, lunar and planetary observing, and computing. For Refere nce A N N U ALS

The Astronomical Almanac (Superintendent of Documents, Washington, D . C . 20402) : U p-to-date i nformation about Sun, Moon, planets, occulta­ tions, and ecli pses . Observer's Handbook (Royal Astronomical Society of Canada, Toronto, Canada): Handy gu ide to celestial events. Many tables . Astronomical Calendar ( Dept. of Physics, Furman U n iversity, Greenville, N C 296 1 3): Ca lendar of celestia l events plus many useful tables and charts. STAR ATLASES Atlases Eclipticalis, Boreal i s, and Austra l i s (Sky Publishing Corp . , Cam­ bridge, MA) . E c l i pticolis contains 32 charts, from + 30° to - 30°, and stars to 9th magnitude. Spectral types indicated by color. Borealis, a companion to Ecliptica lis, has 24 charts, from + 30° to + 90°. Australis has 24 charts, from - 30° to - 90°. Atlas of the H eavens, by A. Becvar (Sky Publishing Corp . , Cambridge, MA): Charts of entire sky show stars to magnitude 7. 75, with c lusters, nebulas, double stars, and variables. Norton's Star Atlas and Telescopic H a ndbook, by Arthur P. Norton (Sky Publishing Corp . , Cambridge, MA): Maps of entire sky show stars to magnitude 6, with c lusters, nebulas, galaxies, and variables. Many pages of valuable information . Pop u l a r Star Atlas (Ga l l and lngliss). A fine small atlas, based on Norton's, showing stars to magnitude 5Y2.

1 46

MAGAZ I N E S

Astronomy ( 6 2 5 E . St. Paul Ave . , Mi lwaukee, WI 5 3 2 0 2 ; monthly): A magazine for the amateur; recommended for beg inners. Sky a n d Telescope (Sky Publishing Corp . , Cambridge, MA; monthly): Fore­ most popu lar magazine on astronomy. News; authoritative; illustrated articles; departments. The Stroll i ng Astronomer (Walter Haas, Box 3AZ, University Park, NM 88003): Journal of Association of Lunar and Planetary Observers. Articles on planets, Moan, etc .

G E N E RAL I N FO RMATION

Amate u r Telescope Making, compiled by Albert G . Inga l l s (Scientific Amer­ ican, Inc . , 4 1 5 Madi son Ave . , New York): Rich in practical information about telescopes. 3 val s . Astronomy, b y Fredrick and Baker (Van Nostrand Reinhol d , N e w York, N Y ) : Standard text. Astrophotogra p hy Basics (Eastman Kodak Co. , Rochester, NY 1 4650): One of the best i ntroductions. Burnha m's Celest i a l H a n d book ( Dover Publications, New York): Descrip­ tive catalog and reference book . Each constel lation with tables, descriptions of objects, many maps and photographs. Celest i a l O bjects for Common Telescopes, Vol . I I , by Rev. T. W. Webb (Dover Publications, New York): Describes nearly 4 , 000 i nteresting objects. A Field Guide to the Stars and Pla nets, 2nd ed . , by Donald Menzel and Jay Pasachoff ( H oughton Mifflin Co . , Boston): Exceptionally good maps; useful combinations of photographs with atlas; fine maps of Moon; tables. Ma k ing Your Own Telescope, by Allyn J. Thompson (Sky Publishing Corp . , Cambridge, MA) : Directions for 6-inch reflector. Skyg uide: A Field Guide for Amateur Astronomers, by Mark R. Char­ trand (Golden Press, N ew York): Technical explanations and constellations vividly i l lustrated ; many practical h i nts on observing; mythological and historical origins of constel lations. Skyshoot i n g , by R . N. and M. W. Maya ll ( Dover Publications, New York): Layman's guide to photography of heavens. Stars, by H . S . Zim and R . H . Baker (Golden Press, New York): Pocket guide with much practical i nformation. Richly i l l ustrated. Stars of the Southern Heavens, by J ames Nangle {Angus and Robertson, Sydney, Austra lia): For observers in southern latitudes . The Stars Belong to Everyone, by Helen Sawyer Hogg ( Doubleday, Inc . , New York): Enjoyable book o n events i n astronomy. Va riable Stars, by W. Strohmeier ( Pergamon Press, New York): Excellent an variables; describes types; many tables and l ight curves.

1 47

Maps of the Heavens T h e c h a rts o n t h i s a n d the f o l l o w i n g p a g e s have been p re­ pared expressly for use with this book. T h e accu racy of t h e c h a rts is con siste n t with t h e i r size. A b o u t 1 ,500 stars, d own to 5th m a g n it u d e , a re pl otted for Epoch 1 900. A l l t h e v a r i a b l es, d o u b l e stars, n ovas1 g a l a x i es, and n e b u l a s l isted el sewhere in the book are located. Symbols a re e x p l a i ned i n keys beneath the cha rts. Where two stars a re too cl ose to s h ow sepa rately, a s i n g l e d i sk with a l i n e t h r o u g h it r e p rese nts bot h . Both may be d e s i g n ated, e . g . ¢' · '.; o r only o n e may be d e s i g n a t e d , e . g . ¢2• Some of the c u stomary con­

stel l a t i o n o u t l i n es have been altered. C o n n ecti n g lines be­ tween stars a re d rown more to help t h e observer "gel a r o u n d " t h a n to represent myt h o l o g i c a l fi g u res. The c h a rts a re i n fi ve pa rts: three for t h e e q u a to r i a l reg i o n , f r o m + 46 ° to - 46 ° , a n d two for the pol a r regions, f r o m + 90 ° to + 44 ° a n d from - 90 ° to - 44 ° . A l o n g the lop of each e q u a ­ t o r i a l c h a rt a p pear i n d ica t i o n s of r i g h t asce n s i o n , a n d at e a c h s i d e , decl i n a t i o n . O n t h e p o l a r cha rts, r i g h t asce n s i o n i s m a r k e d a r o u n d the e d g e , a n d decl i n a ­ t i o n whe re conve n i e n t .

1 48

{continued on

p.

1 56)

Nebula +

;f.

Cluster

Double star ....

N o va

+ No�o

Star magnitudes 0

1

2

3 • 5

•• •• ••

"'

.... \,.

-"•

'

v

_,

.r

"'

"V

L

\ ,....

.-1(

(

•

l

J\l n r

Y,( {

North C i rcumpolar Constel lations

•

+ 30'

•X

TAURU

ERIDANUS

--:=__________!_

-30 '

:

y e Cae

1)

1 50

Stor magn;tvdes

•• 1

2

5 3 4

• • ••

- - -

·

� L

I --- -- I

PICTOR

- �

L v •-- ·· v 1v• I

de

•

/3• L _ -, a•

FEBRUARY 1

Nebula + Cluster ;f.

ll e

I I I<

It

+ 40 '

+ 30 '

+ 20 '

+ 10

•

y

I •'

•

1T

ERIDANUS

c:., I r ei

-10

•P

• cr

-20

8 •

- -

JANUARY 1

Constellation boundaries - - - Star paHerns -- -- --

DECEMBER 1

Double star ... Nova +No• a

Variable stors

Vot

+

NOVEMBER Vw •

-3(

-4(

�·/3 Cor Corol1

a_..

I

p•

Nebula +

L ---,

L

Cluster

;f.-

-

-

•

_fl

_

I

_j

·x ·

I 1 - - __)

, - __�

Constellation boundarie' - - - Star pattern,.- -- --

I

!.___

e•

Double star Nova + NoYo

•G I _j I •O I 1 • >-

I I I ll • • Y .c 1 PYXI S

Variable stars

•

p PUPPI

Vor T Vor

•

Star magnitudes

0

I

2

3 4 5 e •

•• •e

Nebula +

Clustel'

$

A U G U ST 1

Constellation boundaries Star paHerns -- ___

Double star ... Novo + No�a

Variable stan

Vat +

.J U LY VOK •

Dates a l o n g t h e bottom of each e q u a torial c h a rt show the time of y e a r when each con­ ste l l ation is m ost conveniently p l a ced for viewi n g ; that is, when it reaches its hig hest point a bove the horizon (the merid i a n ) a t 9 p . m . A sta r a r rives at the merid ian 4 m i n utes e a r l i e r each n ig ht. E q u atorial c h a rts are used when you are fac i n g away from the poles; polar c h a rts, when facing t h e poles. O n l y observers at the eq uator can see all pa rts of the heavens shown by these c h a rts. Obse rv­ ers in t h e northern hemisphere c a n n ot see some part of the southern skies, a n d to observers in the southern hem isphere some part of the northern skies is invisible. A n observer at + 40° latitude theoretic a l l y has a southern h o­ rizon that c uts the celestial sphere a t - 50 ° declination. But seldom c a n we satisfactorily obse rve a n y o b ject within 1 0 ° of t h e horizon. Therefore the usefu l observing horizon at + 40° l atitude w o u l d be at a b o u t - 40 ° d e c l i nation . For o southern observer at - 40° l ati­ tude, the usefu l northern horizon would be at + 40 ° . Drew a horizontal l i n e on each eq uatorial c h a rt to show your useful observing horizon. Then y o u c a n always tell at a g l a nce which objects are too far south or north for you.

1 56

0

�

0 IJl

�

Nebula + Cluster ;f.

Double star ... Star magnitudes 0

1

2

3 4 s

••••••

•.,�

g•

·�,(. •

•u.

South C i rcumpolar Conste l lations

,p.

._,.

\ :1.

"' •

I

\

•

\

f • -s-

Variable stars

VfM

+

\ \

Vor e

Constellation boundaries Star patterns --

_ __ _

Index Among topics l isted in this i ndex are the 88 constellations s h own o n t h e sta r m a p s (pages 1 48-1 57), wit):. their common names. P a g e n u m­ bers in boldface i n d icate pages where su bjects are i l l ustrated . AAVSO-see A m e r i c a n Association of V a r i a b l e Star Observers A c h e r n a r , 1 04, 1 57 Ad h a r a , 1 04, 1 50 A l q i reo, 1 05, 1 06, 1 55 A l c o r a n d M i z a r , 1 06 , 1 08, 1 48 A l d e b a r a n , 1 04, 1 50 A l g o l , 1 07, 1 1 0- 1 1 3, 1 49 A l i g n me n t , c h e c k i n g , 1 43 - 1 44 A l m a n a c s , 1 46 A l p h a C e n ta u r i , 1 04, 1 57 Alpha Crucis, 26, 1 04, 1 57 A l p h o n s u s , 63, 65 A l t a i r , 1 04, 1 55 Altazimuth mounting, 1 8, 3 5 - 36, 3 7 A m e r i c a n Assoc i a t i o n of V a r i a b l e Star Observers, 1 1 2 - 1 1 3 , 1 46 A m e r i c a n Meteor Society, 1 46 Andromeda, 1 48 , 1 5 1 , 1 54 Andromeda n e b u l a , 1 1 6, 1 5 1 Antares, 1 04, 1 55 A n t l i a ( T h e P u m p ) , 1 53 A p u s ( B i r d of

Parad ise), 1 57

A q u a r i u s (Water C a r r i e r ) , 24, 25, 1 54 A q u i l a ( Ea g l e ) , 1 54, 1 55 Ara ( A l t a r ) , 1 57 Arcturus, 1 04, 1 52 A r i e s ( R a m ) , 24, 25, 1 5 1 Ari starc h u s , 6 5 Assoc i a t i o n of L u n a r a n d P l a netary O bservers, 1 46 Aste r o i d s , 24, 26, 86-88 Astra-camera, 1 26- 1 27 Astronauts, 6 1 A t l a ses, star, 1 0- 1 1 , 45-50, 1 46

1 58

Atmospheric effects, 29 -30, 39, 56, 57 Auriga ( C h a r i otee r ) , 1 49, 1 50 A u roras, 70, 75-77; d r a w i n g , 1 24 ; photogra p h m g , 1 30- 1 3 1 , 1 33 B a r l o w l e n s , 39, 1 22, 1 38, 1 39 Be l l a t r i x , 1 04, 1 50 Beta Centa u r i , 1 04, 1 57 Beta C r u c i s , 26, 1 04, 1 57 Bete l g e u s e , 3 1 , 32, 34, 1 04, 1 50 Big D i pper, 22, 33, 1 48 , 1 53 B i n o c u l ars, 7 1 1 - 1 2, 33 ., Books, 1 0, 1 4o - 1 47 Bootes ( H erdsm a n ) , 1 48, 1 52 C oe l u m ( B u r i n ) , 1 50, 1 57 C a m e l opard a l i s ( G i ra ff e ) , 1 48 C a meras, 8, 1 25 - 1 32 C a n c e r ( C ra b ) , 25, 1 50, 1 53 Canes Venatici ( H u n t i n g Dog s ) , 1 48, 1 52 C a n i s M a j o r (Great Dog ) , 1 50 Canis Minor ( little Dog ) , 1 50 C a n o p u s , 1 04, 1 57 C a pe l l a , 1 04, 1 48 , 1 50 C o p r i c o r n u s (Goa t ) , 2 5 , 1 54 C a r i n a ( Ke e l of S h i p Arg o ) , 1 57 C a s s i o p e i a , 1 49, 1 54 Ca stor, 1 04, 1 06, 1 50 C e l e s t i a l sphere, 2 0 C e n t a u r u s ( C e n ta u r } , 1 52, 1 53, 1 57 C e p h e u s ( K i n g ) , 1 49 Cetus ( W h a l e ) , 1 5 1 , 1 54 C h a m a e l e o n , 1 57

C h a rts-se e Sta r s : cha rts C i rc i n u s (Compasse s ) , 1 57 C l o c k d r i v e, 1 28 , 1 38 C l u sters, 32, 50-51 , 1 05, 1 08- 1 09, 1 1 0 ( t a b l e ) ; photog r a p h i n g , 1 3 1 C o a 1 Sack, 44 C o l u mba ( D ove ) , 1 50 Coma Berenices ( Be r e n i c e ' s H a i r ) , 1 52 C o m ets, 4 , 94-97, 1 00, 1 3 1 , 1 33 C o n j u n c t i o n s , 80 C o n ste l l a t i o n s , 3 1 -32, 1 03; c h a n g e w i t h s e a s o n s , 23; maps, 1 48- 1 57 ; zod iac , 24-25 C o o � i n ates, u s e of, 47, 48, 49-53 C orona A u stra l i s ( S o u t h e r n C rown ) , 1 55 Corona Borea l i s ( N o rthern C row n ) , 1 52, 1 55 C o r v u s ( C ro w ) , 1 52, 1 53 C o u nterg l o w , 77 C r a b N e b u l a , 1 1 9, 1 20, 1 21 C rater ( C u p ) , 1 52, 1 53 C r u x ( C r o s s ) , 1 57

Cyg nus (Swa n ) , 27, 1 48, 1 54, 1 55

Dawes' l i m i t , 1 7 D e c l i n a t i o n , 45; c i r c l e , 51 Delphinus (Dolphin) , 1 54 Deneb, 1 04, 1 48, 1 54 Dew cap, 1 07, 1 45 D i a g o n a l star, 1 4, 37 D i rect i o n s in s k y , 3.4 D i stances, e s t i m a t i n g , 3 2-33 D o rado ( G o l d f i s h ) , 1 57 D o u b l e c l u ster, 1 03, 1 09, 1 1 0, 1 47 D o u b l e stars, 1 05, 1 06 (tab l e ) , 1 07 , 1 08

Draco ( D ra g o n ) , 1 49 D r a w i n g sky o b j ects, 1 22 - 1 24

H y d r u s , 1 57

E a rth s h i n e , 55 E c l i p se" d r a w i n g , 1 24; lunar, 63-65 ; p h o t o g ra p h i n g , 1 29, 1 32 ; s o l a r, 70-73, 1 3 2 E c l i p t i c , 24-25 E l o n g a t i o n , 80 E p s i l o n lyrae, 1 05, 1 08, 1 55 Equatorial mounting, 1 0, 35, 1 3 8 E q u i n o x , v e rn a l , 48 E q u i p m e n t : basic, 1 0 - l 9 ; c a re of, 1 4 1 1 45 ; extra, 1 3 8- 1 4 1 E q u u l e u s ( C o l t ) , 1 54 E r i d a n u s ( R i v e r ) , 1 50, 1 5 1 , 1 57 Eta Carinae nebula, 40 Even i n g star, 79, 83, 92 (table) Eyepieces, 1 5- 1 7, 3 8 - 3 9 ; m u l t i p l e , 1 39; s e l e ct i n g , 3 8 - 3 9 ; speci a l , 3 9 , 1 39 ; s t o r i n g , 1 43 E y e s , use o f , 30-3 1 , 4 1 -42

J u l i a n d a y , 1 36 J u p aer, 4 , 36, 79, 88; d ra w i n g , 1 24; m o o n s , 7, 8, 88-89; occu l t a l i o n , 64-65

F i e l d of v i e w , 1 2 , 3 8 - 3 9 F i l m s , 1 29 - 1 32 F i lters, c o l o r , 1 39- 1 40 F i nd e r , 4 1 , 1 42 F i re ba l l , 98 Focal l e n g t h , 1 5 F o r m a l h a ut, 49-50, 1 04 , 1 54 Fornax ( Furnace), 1 5 1 Ga l a x i e s, 1 02 , 1 1 6, 1 1 7, 1 20 ( t a b l e ) Geg e n s c h e i n , 7 6 Ge m i n i ( Tw i n s ) , 2 5 , 1 50, 1 53 Greek a l p h a bet, 46 Grus ( C r a n e ) , 1 54, 1 57 Halo, lunar, 56 H e r c u l e s , 1 48, 1 52 , 1 55; c l u ster, 4, 32, 50 ( m a p ) , 1 09 H o ro l o g i u m ( C l oc k ) , 1 57 H o u r a n g l e , 52 H o u r c i r c l e , 53 H yades, 1 09, 1 50 H y d ro (Sea Serpe n t ) . 1 52, 1 53

I n d u s ( I nd i a n ) , 1 56

lace rta ( l i z a rd ) , 1 49, 1 54 leo ( l i o n ) , 25, 1 53 leo M i n o r ( l i t t l e l i o n ) , 1 48, 1 53 l e p u s ( H a r e ) , 1 50 l i bra (Sca l e s ) , 25, 1 52 l i g h t - g a t h e r i n g power, 1 4, 1 5 , 1 7 l i t t l e D i p per, 26, 1 49 loca t i n g objects, 3 1 -34, 45-53 low e l l , Perciva l , 9 3 lunar p h e n o m e n a -see Moon l u p u s ( W o l f ) , 1 52 , 1 55, 1 57 l y n x , 1 48, 1 50, 1 53 lyra ( l y r e ) , 1 55 M 1 3 c l u ster, 4 , 32, 50, 1 09, 1 53 M 3 1 n e b u l a , 1 1 6, 1 1 7, 1 20, 1 49 M42 n e b u l a , 3 1 , 1 1 8, 1 25, 1 48 M44 custer, 1 1 0, I l l , 151 M 8 1 n e b u l a , 52, 1 47 M a g a z i n e s , 1 47 M a ge l l a n i c C l ou d s , 1 2 1 , 1 57 M a g n i f y i n g power, 1 2, 1 3 , 1 5- 1 7, 27, 38-39 M a g n i tu d e s , 26; v i s i b l e i n objectives o f various sizes, 1 4 M a p s , star, 1 48 - 1 57 Mars, 5, 78, 84-87; d e ta i l s o n , 43, 86; d r a w i n g , 1 24 ; f i l te r used for, 1 40 ; o p p o s i t i o n s , 87 Mec h a n i c a l d r i ve s , 1 28, 1 3 8 Mensa ( T a b l e M o u n ta i n ) , 1 57 Mercury, 78-83; transit, 8 M e s s i e r l i st, 1 06 Meteorites, 99, 1 00

Mete o r s, 4, 98-1 0 1 , 1 30 - 1 3 1 , 1 34 M i c roscop i u m ( M i croscope ) , 1 54 M i l k y W a y , 44, 1 04 - 1 05 Minor p l a n e t s , 24, 26, 86-88 M i ra ( O m icron Ceti ) , 1 1 1 , 1 1 2, 1 1 4, 1 5 1 M i rror o f reflector, 1 4, 1 6, 1 43 - 1 44 M i z a r a n d AI cor, 1 06, 1 08, 1 48 Monoceros ( U n i co rn } , 1 50, 1 53 M o o n , 4, 54-65; c o l o r s , 56-57; craters, 58-63, 1 22 ; d ra w i n g , 1 22- 1 23; e c l i p s e , 63-65, 1 29 ; far side, 6 1 ; features, 60-62 ; h a l o , 56; magn ifications, 1 2 , 38-39; mop, 58; p h a s e s , 55, 60; p h otog ra p h i n g , 1 3 2 Morn i n g star, 79, 83, 92 ( ta b l e ) M o u n t i n g s-see A l ta z i m u l h ; Equatorial M u sca ( F l y ) , 1 57 N e b u l a s , 4, 40, 52, 1 1 7- 1 2 1 ; d r a w i n g , 6, 1 24; p h o t o g ra p h i n g , 1 3 l ; r i n g , 4, 1 1 9, 1 30 N e p t u n e , 79, 9 1 -92, 9 3 ( ma p ) N o r m a ( le ve l ) , 1 52, 1 57 N o r t h Star, 26, 1 49 N o r t h e r n l i g htssee A u roras Novas, 4 , 1 1 4, 1 1 5 (table) Objective, 1 2- 1 7 Observatory, 1 4 1 Occu l t a t i o n s , 64-65 Octans (Octa n t ) . 1 57 O m i cron Ceti-see M i ra O p h i u c h u s (Serpent Beare r ) , 1 55 O p p o s i t i o n , 80- 8 1 Organizations, a m ateur, 9, 1 1 2 - 1 1 5, 1 46 O r i o n , 3 1 -32, 1 50 ; n e b u l a , 3 1 , 1 1 8 , 1 25 1 48; s t a r t ra i l s , 1 27 Pavo ( P e a cock) , 1 57

1 59

Pegasus ( F l y i n g Horse) , 1 5 1 , 1 54 P e r s e u s , 1 48, 1 50, 1 5 1 ; d o u b l e c l u ster, 1 03 , 1 09, 1 1 0, 1 47 P h o e n i x , 1 5 1 , 1 54, 1 56 Photography, 8 , 1 25- 1 32 P i ctor ( P a i n ter o r E a se l ) , 1 50, 1 57 P i sces ( F i s h e s ) , 24 1 5 1 , 1 54 P iscis Austrin u s ( S o u t h e r n F i s h ) , 1 54 P l a n et o i d s - s e e Aste r o i d s P l a nets, 78-93; b r i g h t n e s s , 27; deta i l o n , 42 ; d ra w i n g , 1 23 - 1 24; i n fe r i o r , 80; l oca t i n g , 8 0 , 92 ( t a b l e ) ; m i n o r , 24, 2 6 , 8 6 - 8 8 ; m o t i o n , 24; p h otogra p h i n g , 1 3 2; s u pe r i o r , 80, t a b l e of data, 85 P l a n i sphere, 1 1 , 3 1 P l e i a d e s , 2 8 , 1 08 - 1 09, 110 P l u to, 93 P o i nters, the, 33, 1 47 P o l a r i s , 26, 1 49 P o l l u x , 1 04, 1 50 Procyon, 1 04, 1 50 Prox i m a C e n ta u r i , 1 02 P u p p i s (Stern of s h i p A r g o ) , 1 50, 1 53, 1 57 P y x i s ( C o m p a s s ) , 1 53

Q u a d r a t u r e , 80

R a i n bow, 74 Ref l ector, 7 - 8 , 1 0, 1 4, 1 6, 4 1 , 1 42 - 1 45 (see a l so T e l e s copes) Refractor, 7 - 8 , I 0, 1 4, 1 6, 4 1 , 1 42 - 1 45 ( see a l so Tel escopes) �e g u l u s , � 04, 1 53 �esol v i n g power, 1 7, 1 8 R e t i c u l u m ( N e t ) , 1 57 Rho Ophiuchi region, 118 R i g e l , I 04, 1 50 R i g h t a s c e n s i o n , 45 R o y a l Astro n o m i c a l S o c i e t y of N e w Zea l a n d , 1 46

1 60

Sag itt a (Arrow ) , 1 54, 1 55 S a g i tta r i u s (Arc h e r ) , 25, 1 54, 1 55 Satu r n , 1 9, 79, 8 9 - 9 2 ; d r a w i n g , 1 24 Scorp i u s (Scorp i o n ) , 2 5 , 1 52, 1 55 S c u l ptor, 1 5 1 , 1 54 S c u t u m ( S h i e l d ) , 1 55 See i n g cond i t i o n s , 29-30 Serpens ( S e r p e n t ) , 1 52, 1 55 Sett i n g c i rc l e s , 1 8 , 50-53 Sexta n s (Sexta n t ) , 1 53 S h a u l a , 1 04, 1 55 Shoot i n g stars-see Meteors Sidereal time, 5 1 · 53, 1 36 - 1 37 S i r i u s , 1 04, 1 50 S k y : d i rections, 34; d i stances, 32-33; motion a n d appear­ ance of, 2 1 -25 S o l a r observ i n g , 66-73 Solar p h e n o m e n a - see Sun S o l stices, 25 Southern C r oss, 26, 44, 1 57 Southern l i ghts-see Au roras S p i ca , 1 04, 1 52 Star d i ago n a l , 1 4 , 37 Stars, 1 02 - 1 1 5 ; a t l a ses, 1 46 ; b r i g htest ( ta b l e ) , 1 04 ; b y seasons, 23 - 24 ; c h a rts, 34, 4 3 , 5 3 , 1 48 - 1 57 ( m o p s ) ; c l u sters, 2 8 , 3 1 , 3 2 , 5 0 , 1 08, 1 1 0 ( ta b l e ) , 1 1 1 ; colors, 1 05, 1 06; d e s i g n a t i o n s , 46; d o u b l e , 1 05, 1 06 ( ta b l e ) ; m a p s , 1 48 - 1 57; m o t i o n s , 2 1 - 24; m u l t i p l e , 1 05 , 1 06 ( ta b l e ) , 1 08 ; n a m e s , 46; tra i l s , 1 27 , 1 30 ; v a r i a b l e , 53 ( c h a rt ) , 1 09- 1 1 5, 1 1 3 ( ta b l e ) . See a l so a s l i sted by n a m e . S u n , 66-73; c h a n g i n g p a t h, 23; d e v i c e s f o r obser.v i n g , 67-68; d o g s , 75; e c l i p ses, 4 , 70-73, 1 3 2; photo­ g ra p h i n g , 1 3 2 ; p i l l a r ,

7 4 ; s p o t s , 4, 6 7 , 69-70 T a u r u s ( B u l l ) , 24, 1 50 , 151 T e l e s c o p e s : a l i g n m e n t, 1 43- 1 44 ; d e s i g n s , 1 3 1 8; homemade, 7 , 8 , 9 ; m a i ntenance, 1 4 1 1 4 5; m o u n t i n g s , 1 0, 1 8 ; o r i e n t i n g , 35-37; refract i n g v s . reflect­ ing, 7-8, 10; r i c h ­ f i e l d , 1 07, 1 4 1 ; s i g h t i n g , 40- 4 1 ; s o l a r o b se r v i n g , 66-73 T e l e s co p i u m ( T e l e s c o p e ) , 1 56 T i m e , 1 35 - 1 37; s i derea l , 5 1 -53, 1 36-1 37; s i g ­ n a l s , 6 5 ; zones, 1 35 Tom b a u g h , C l yde, 93 T r a n s i t s , 8, 83 Tria n g u l u m (Tria n g l e ) , 1 51 T r i a n g u l u m Au stra l e (Southern Triangle) , 1 57 T u c a n a ( T o u ca n ) , 1 56

U r a n u s , 79, 9 1 , 93 (map) U r s a M a j o r ( G reat Bea r ) , 22, 33, 1 48 , 1 53 U rsa M i n o r ( l i tt l e Bear) , 2 6 , 1 49

V a r i a be stars, 1 09 - 1 1 5 Vega, 5 1 , 1 04, 1 55 V e l a ( sa i l s of s h : p A r g o ) , 1 53, 1 57 V e n u s , 78, 79, 8 1 - 8 3 Vernal equinox, 48 V i rg o ( V i rg i n ) , 25, 1 53 V i s i o n , 30- 3 1 ; averted, 3 1 , 42 Volens ( F l y i n g F i s h ) , 1 57 V u l pecu l a ( F o x ) , 1 54, 1 55

Z o d i a c, 24-25, 7 8 Z o d i a ca l l i g h t , 75-76

K L

THE SKY OBSERVER'S GUIDE A GOLDEN GUIDE® NEWTON and MARGARET MAYALL are well known

among both professional and amateur astronomers. Mr. Mayall, who is a consulting engineer, has been active in astronomy since youth . Mrs . Mayall, formerly Pickering Memorial Astronomer at Harvard Observatory, is Direc­ tor Emeritus of the American Association of Variable Star Observers (AAVSO), the largest organization of active amateurs . JEROME WYCKOFF has edited many popular books on

science. He is the author of The Story of Geology and co­ author of the Golden Guide Landforms. An amateur as­ tronomer himself, Mr. Wyckoff has been a member of AAVSO for many years.

The late JOHN POLGREEN, a devoted amateur astrono­ mer, once made his own 8-inch reflector. Mr. Polgreen and his wife Cathleen, both members of AAVSO, spent countless evenings sketching moon and planets . Mr. Pol­ green's paintings appear in The Golden Book of Astronomy and other popular books . With Mrs. Polgreen he wrote and illustrated The Earth in Space. HERBERT S. ZIM, Ph . D. , Sc . D. , an originator and former

editor of the Golden Guide Series, was also an author for many years . Author of some ninety books and editor of about as many, he is now Adjunct Professc;>r at the Uni­ versity of Miami and Educational Consultant to the Amer­ ican Friends Service Committee and other organizations. He works on educational, population and environmental problems.

GOLDEN P R E S S • N E W YORK

24009-4

A GOLDEN GUIDER