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A Guide to the Constellations, Sun, Moon, Planets, And Other Features of the Heavens
By Herbert S. Zim, Robert H. Baker, James Gordon Irving
St. Martin's PressCopyright © 2001 St. Martin's Press
All rights reserved.
OBSERVING THE SKY
Stars and planets have attracted man's attention since earliest times. Ancient tablets and carvings show that movements of planets were understood before 3000 B.C. Legend says two Chinese astronomers who failed to predict an eclipse correctly in 2136 B.C. were put to death. The Egyptians placed their pyramids with reference to the stars. The circles of stone at Stonehenge may have been used to keep track of lunar eclipses. Astronomy is indeed the oldest science, yet its importance increases as scientists turn to the stars to study problems of physics which they cannot tackle directly in the laboratory.
As far back as history records, there were professional astronomers — long before there were professional zoologists and botanists. The Egyptians, Chinese, and Europeans had court astronomers. Their work often involved trying to predict future events, but their system, though considered unscientific today, involved observation and recording of facts about stars and planets. These early astronomers, as well as those of today, made remarkable discoveries that changed man's outlook on the world and himself.
There has always been, too, an army of amateurs studying and enjoying the stars. Some make practical use of their knowledge — sailors, pilots, surveyors — but most study the heavens out of sheer interest and curiosity.
WHY LOOK? The stars can tell you time, direction, and position. These are about their only practical use to an amateur. More important is the satisfaction one finds in recognizing the brightest stars and planets. To see and to recognize Leo in the eastern sky is akin to seeing the first robin. And, as you learn more about the stars and the variety of other celestial objects, the more the wonder of the heavens grows.
WHERE TO LOOK Star-gazing has no geographic limits. Some stars can even be seen from brightly lit, smoky city streets, but the less interference from lights or haze the better. An ideal location is an open field, hill, or housetop where the horizon is not obscured by trees or buildings. However, buildings or a hill may also be used to screen off interfering lights, and although you may see less of the sky this way, you will be able to see that part of it better.
WHEN TO LOOK Only the brighter stars and planets are visible in full moonlight or soon after sunset. At these times the beginner can spot them and learn the major constellations, without being confused by myriads of fainter stars. On darker nights, without moonlight, one may observe minor constellations, fainter stars, nebulae, and planets. Stars and planets visible at any given hour depend on time of night and season of the year. As the earth rotates, new stars come into view in the eastern sky as the evening progresses. Late at night one can see stars not visible in the evening sky until several months later. The seasonal star charts here, here, here, and here and planet tables show the location of major celestial objects at various times of the year. See check list.
HOW TO LOOK First, be comfortable. Looking at stars high above the horizon may cause a stiff neck and an aching back; so use a reclining chair, a couch, or a blanket spread on the ground. Remember — ground and air may be unexpectedly cold at night; warm clothing, even in summer, may be needed. How to look also involves a method of looking. The section on constellations here gives suggestions. Many observations require knowing a little about angles in the sky; After you have become familiar with the more common stars, constellations, and planets, a systematic study may be in order — perhaps with field glasses. By that time your interest may lead you to some of the activities suggested on the following pages.
EQUIPMENT You need no equipment, except your eyes, to see thousands of stars. This book will point the way to hours of interesting observation with your eyes alone. Later you will find your enjoyment greatly enhanced by the use of field glasses (6- to 8-power) such as those used in bird study. With these you can see vastly more — details on the moon, moons of Jupiter, many thousands of stars, star clusters, double stars, and nebulae. Larger field glasses (12-, 15-, or 18-power mounted on a tripod) will reveal finer lunar details and more hundreds of exciting stellar objects. Some day you may buy or make your own telescope.
ACTIVITIES FOR THE AMATEUR
ENJOYING THE STARS It is worth repeating that night-by-night observing, studying, and enjoying the stars is the activity that can mean the most to most people. No equipment and little preparation are needed. This book and sources of information suggested will help.
IDENTIFICATION The enjoyment of stars involves some practice in identification. Knowing two dozen constellations and a dozen of the brightest stars is often enough. A systematic study of stars, the identification of lesser constellations, and the location and study of clusters and nebulae demand more intensive efforts. A serious amateur will benefit by knowing nearly all the constellations and bright stars before going deeper into any phase of astronomy.
FOLLOWING THE PLANETS The planets, moving along in their orbits, are constantly changing their positions. Even the beginner can become familiar with the movements of planets — can recognize them, and predict which way they will travel. Knowing the planets is as important and as enjoyable as knowing the stars.
MUSEUMS Many museums have astronomical exhibits worth seeing. These may include meteorites, photographs of stars and planets, and sometimes working models of the solar system. Museums may be found at universities, observatories, planetariums, or governmental institutions. Inquire locally or when traveling concerning museums in the area that may offer astronomical exhibits.
OBSERVATORIES These are the sites of the great optical and radio telescopes where professional astronomers work. When work is going on, astronomers cannot be disturbed. However, many observatories are open for tours at specified hours, and some offer a schedule of public lectures. Some of the major places you can visit are listed here, and others are given in references on here.
Kitt Peak National Observatory, Tucson, AZ
National Radio Astronomy Observatory, Greenbank, WV
Mt. Wilson Observatory, Los Angeles, CA
U.S. Naval Observatory, Washington, DC
Allegheny Observatory, Pittsburgh, PA
PLANETARIUMS These "indoor universes" offer the chance to see and learn the sky under the instruction of experts. Sky shows also explain astronomical concepts. In addition to hundreds of small planetariums in schools and smaller museums, among the major planetariums are:
Hayden Planetarium, New York, NY
Adler Planetarium, Chicago, IL
Fels Planetarium, Philadelphia, PA
Griffith Planetarium, Los Angeles, CA
Fernbank Planetarium, Atlanta, GA
Charles Hayden Planetarium, Boston, MA
Morrison Planetarium, San Francisco, CA
Davis Planetarium, Baltimore, MD
Buhl Planetarium, Pittsburgh, PA
CLUBS AND ASSOCIATIONS Amateur astronomers often band together to share their experiences and interests. Clubs are found in most large cities and many smaller ones. At meetings, a lecture or discussion is usually followed by a period of observing through telescopes. Some clubs work on cooperative projects in which the members share some scientific investigation. Visitors are usually welcome, and membership is commonly open to anyone who is interested.
Through such activities anyone from a youth in high school to a retired couple can become serious amateurs. Such amateurs spend much of their time working on an astronomical hobby. They often become experts; some have made important discoveries. Professional astronomers are glad to have the help of trained amateurs, and several fields of astronomical research are manned largely by them. Amateur activities that demand greater skill and experience offer greater rewards in the satisfaction they provide.
TELESCOPE MAKING Making a telescope requires time and patience. But in the end you have an instrument costing only a small fraction of its worth, plus the fun of having made it. The telescopes made by amateurs are usually of the reflecting type, with a concave mirror instead of a lens for gathering light. Telescope-making kits, including a roughly finished glass "blank" for the mirror, other telescope parts, and complete instructions, are available from some optical-supply firms.
OBSERVING METEORS Meteors or shooting stars often occur in well-defined showers. Careful observation and plotting of the paths of meteors yield information of scientific value. A number of groups of amateurs are engaged in observing meteors, and any interested amateur or group of amateurs can join. Contact the American Meteor Society, Dept. of Physics and Astronomy, State University, Geneseo, NY 14454.
OBSERVING VARIABLE STARS Amateurs with telescopes have done unusual work in this advanced field. Studies of these stars are coordinated by the American Association of Variable Star Observers, 187 Concord Ave., Cambridge, Massachusetts 02138. The director of the Association will be glad to furnish qualified amateurs with details about this work.
STELLAR PHOTOGRAPHY Photographing the stars and other heavenly bodies is not difficult. Excellent pictures have been taken with box cameras set firmly on a table. But pictures of faint objects must be taken with a telescope or with a special camera adjusted to compensate for earth's motion. Photography is an important tool of astronomers — one which the amateur can use to good advantage.
MORE INFORMATION This book is a primer to the sky and can only introduce a story which is more fully told in many texts and popular books on astronomy.
Abell, George O., Exploration of the Universe, 3rd ed., Holt, Rinehart, and Winston, New York, 1975. One of the best college level textbooks.
Bok, Bart J. and Priscilla E., The Milky Way, 4th ed., Harvard University Press, Cambridge, 1974. An engaging introduction to our own galaxy by two renowned experts.
Chartrand, Mark R., Skyguide, Golden Press, New York, 1982. This excellent introduction to the sky and to astronomy in general bridges the gap between books such as this one and textbooks. It contains seasonal sky maps and detailed charts of all the constellations.
Kirby-Smith, H.T., U.S. Observatories: A Directory and Travel Guide, Van Nostrand Reinhold, New York, 1976. Information on visiting observatories and other astronomical sites.
Lum, Peter, The Stars in Our Heavens, Pantheon Books, New York, 1948. A delightful recounting of sky mythology from around the world.
Mayall, Mayall, and Wyckoff, The Sky Observer's Guide, Golden Press, New York, 1965. An introductory book for the layman with maps of the heavens.
Norton, Arthur P., Norton's Star Atlas, Sky Publishing Corp., Cambridge, 1978. An excellent first sky atlas useful with binoculars or a small telescope.
Shipman, Harry L., Black Holes, Quasars, and the Universe, 2nd ed., Houghton Mifflin Co., Boston, 1980. An exciting introduction to recent astronomical discoveries.
Astronomy, AstroMedia Corp., P.O. Box 92788, Milwaukee, WI 53202.
Mercury, Astronomical Society of the Pacific, 1290 24th Ave., San Francisco, CA 94122.
Sky and Telescope, Sky Publishing Corp., 49 Bay State Rd., Cambridge, MA 02138.
OUR UNIVERSE is so vast that its limits are unknown. Through it are scattered millions of galaxies of various sizes and shapes. In a galaxy like one shown here (3), our sun and the earth are located here. Galaxies contain hundreds of millions, even hundreds of billions, of stars of many types (1), ranging from red supergiants less dense than the earth's atmosphere to white dwarfs hundreds of times denser than lead. Stars on the average are spaced several light-years apart, but may be closer in some clusters (2). Planets may revolve around many of the stars.
OUR SOLAR SYSTEM is located halfway from the center of our galaxy — the Milky Way. Around the sun revolve the nine major planets with more than four dozen satellites; also hundreds of thousands of asteroids and swarms of meteors. Here we see the planets (1) in their orbits around the sun (see here) and (2) in the order of their size. The asteroid Ceres is compared (3) to Texas for size, and the moon is compared (4) to the United States. A comet's orbit (5) appears in red. Our solar system may be only one of billions in the universe. So far, life is known to exist only on earth.
THE SUN is the nearest star. Compared to other stars it is of just average size; yet if it were hollow, over a million earths would easily fit inside. The sun's diameter is 860,000 miles. It rotates on its axis about once a month. The sun is gaseous; parts of the surface move at different speeds. The sun's density is a little under 1 ½ times that of water.
The sun is a mass of incandescent gas: its core is a gigantic nuclear furnace where hydrogen is built into helium at a temperature of millions of degrees. Four million tons of the sun's matter is changed into energy every second. This process has been going on for billions of years, and will continue for billions more.
The sun's dazzling surface, the photosphere, is speckled with bright patches and with dark sunspots. Rising through and beyond the chromosphere, great prominences or streamers of glowing gases shoot out or rain down. The corona, which is the outermost envelope of gases, forms a filmy halo around the sun.
It is unsafe to observe the sun directly with the naked eye or binoculars. Use a special filter, a dark glass, or a film negative to protect your eyes. When a telescope is used, project the sun's image on a sheet of paper.
SUNLIGHT Every square yard of the sun's surface is constantly sending out energy equal to the power of 700 automobiles. About one two-billionth of this, in the form of sunlight, reaches us. Sunlight is a mixture of colors. When it passes through a glass prism, some of the light is bent or refracted more than other portions. Light leaving the prism spreads out into a continuous band of colors called a spectrum. Colors grade from red, which is bent least, through orange, yellow, green, and blue to violet, which is bent most.
The spectrum is crossed by thousands of sharp dark lines. These indicate that some light was absorbed as it passed through the cooler gases above the sun's surface. These gases absorb that part of the sunlight which they would produce if they were glowing at a high enough temperature. Thus a study of the dark lines in the solar spectrum (called Fraunhofer lines, after their discoverer) gives a clue to the materials of which the sun is made. Of the 92 "natural" elements on the earth, 2/3 have been found on the sun. The rest are probably present also. From the shifting of spectral lines, astronomers can measure the rotation of the sun and the motions of stars. They can detect magnetic fields from spectral lines and can determine a star's temperature and its physical state. Although astronomers can only see the surface of a star, they can calculate what it must be like deep inside.
RAINBOWS are solar spectra formed as sunlight passes through drops of water. Rainbows may be seen when a hose is adjusted to a fine spray. The drops act like prisms, refracting sunlight to produce the spectrum.
A single, or primary, rainbow has red on the outside, violet inside. The arc is 40 degrees in radius. The center of the arc is always opposite the sun. When you see a bow, the sun is behind you. Sometimes a secondary rainbow forms outside the primary. It is fainter, with colors reversed — red inside, violet outside. The secondary bow forms from light reflected twice within drops. Light may be reflected more than twice, so occasionally up to five rainbows are seen. Another type of bow — red, or red and green — may appear with primary and secondary bows.
SUNSPOTS often appear on the sun's photosphere — appearing as dark, sculptured "holes" in contrast to the bright white surface. These sunspots are sometimes so large they can be seen with the unaided eye (through a dark glass for protection, of course), and are most easily observed when the sun is low on the horizon. The use of field glasses or a small telescope helps, but the safest method of observation is to study photographs. The dark center, or umbra, of a sunspot varies from a few hundred to over 50,000 miles across. This is surrounded by a less dark area, a penumbra, that often doubles the size of the sunspot. As the sun rotates, new sunspots come into view. Most persist for a week or so, but the maximum duration is from three to four months.
Excerpted from Stars by Herbert S. Zim, Robert H. Baker, James Gordon Irving. Copyright © 2001 St. Martin's Press. Excerpted by permission of St. Martin's Press.
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