The maps in this book are drawn exactly for a latitude of 40 degrees North -- the parallel for Philadelphia, Indianapolis, Denver, Reno, northern Japan, Korea, Peking (China), Ankara (Turkey), northern Greece, the "foot of the boot" of Italy and Madrid (Spain). However, they will serve amply well for places as far as six or seven degrees north or south of this specific latitude (or 400 to 500 miles), thus accommodating approximately 20 per cent of the world's population.
From a position north of the fortieth parallel an observer will be able to see some stars that are beyond the northern horizon indicated on our maps, and he will be unable to see some stars that are represented near the southern horizon on our maps. Conversely, from a position south of the fortieth parallel an observer will have a more extensive view to the south and a less extensive view to the north.
Another convention we have had to adopt is that of showing the sky for the times given for the exact Standard Time meridians. Determine what Standard Time is used in your area and the longitude corresponding to it. Eastern Standard Time is based on longitude 75 degrees West; Central Standard Time on longitude 90 degrees West; Mountain Standard Time on longitude 105 degrees West; Pacific Standard Time on longitude 120 degrees West. Then, determine your own longitude, from an atlas. Take the difference in degrees between your own longitude and that of your appropriate Standard Time meridian; multiply it by 4 to convert the degrees into minutes of time. If you are east of the Standard Time meridian, subtract the minutes from the time given on the map to determine the moment to see the sky as pictured; if you are west of the Standard Time meridian, add the minutes of longitude correction to the time given.
A glance at the maps will suffice to show how to use them. The words "Looking North," "Looking East," etc., serve to orient the maps to match the sky. If you look east, the words "Looking East" should be right side up, and so on.
The charts are arranged more or less in the form of what is called a Formée Cross, except that the sides of the panels are convex instead of concave. This largely eliminates distortion; the star groups have nearly the same shapes in the sky and on the maps. If a group straddles a division between two panels of the cross, reference to a preceding or following map will show the whole outline. Many star maps designed for the beginner permit so much distortion that they defeat their purpose; practically no one who is not already acquainted with the constellations can recognize them on those maps. Too many such star charts, showing all of the sky in circular form, with the pole or zenith in the center, or half the sky as half of a circular disk, with the zenith at the top, have been circulated with too little regard for the possibility of practical use by a beginner.
Undoubtedly, many deviations from exact representation of the heavens will be spotted in the maps in this book, but they are comparatively small; moreover, because of the "open" appearance of the charts, resulting from the elimination of vast numbers of faint stars, there is never much chance for confusion.
Many people do not know that red light promotes and maintains dark adaptation -- the ability of the eyes to see faint objects out-of-doors after leaving a brightly lighted house. In using the maps out of doors, a flashlight with two or three layers of red cellophane over the lens can be used, to make sure that the stars on the maps can be seen, while at the same time the stars in the sky will be plainly visible.
Some classicists may object to the mixture of Greek and Roman names in the myths. We know that the Romans borrowed the Greek myths, which in turn the Greeks had borrowed from the Phoenicians, who had borrowed them from the Babylonians, and so on. The names of the characters given here are, it is believed, the commonest ones associated with them. Many good books have been devoted to mythology per se; they can be found on most library shelves.
A very exhaustive book for those who wish to know the origins of the names of stars is Allen's Star Names and Their Meanings, which contains a wealth of information about the constellations; it has long been out of print, but it is available in many libraries. Much of the history is found in Basil Brown's Astronomical Atlases, Maps and Charts; this too is out of print, but can be found in some libraries.
Those who find their appetites whetted by this elementary book of maps may care to go on to a more advanced atlas, in which many more stars, as well as the Bayer and Flamsteed designations, are given. Those by Schurig-Götze and by Norton are good ones. The most modern is Antonin Becvar's de luxe Atlas of the Heavens, which can be purchased in a less expensive edition called Field Atlas of the Heavens. Prices of many such publications can be obtained from the Sky Publishing Corporation, Harvard Observatory, Cambridge 38, Mass., which also publishes a fine monthly astronomical magazine, Sky and Telescope.
Many amateurs (beginners, really) have asked the authors to recommend material that would be helpful in pursuing the subject. The first thought would be to consult school and public libraries; even if the selection is small and poorly chosen, the beginner can profit by reading through it. Then, with references to newer publications in such journals as Sky and Telescope, the better volumes being printed today can be obtained or, perhaps, recommended to the libraries. The volume of material in this Space Age is enormous.
THE HISTORY AND DEVELOPMENT OF THE CONSTELLATIONS
Modern astronomy has become a highly specialized study, with a good knowledge of at least elementary physics and mathematics required to follow its many ramifications. We could hardly expect it to be otherwise, in a science which attempts to embrace as its field the whole of creation -- the universe.
The findings of modern astronomy make fascinating reading for one who is willing to realize that no one can expect to grasp quite all of what is contained even in a so-called "popular" book, without at least some measure of concentration and connected thought. This is not peculiar to astronomy, of course; modern physics, chemistry, geology, botany -- even economics and political science -- are such specialized subjects that the general reader must appreciate his handicaps and must not expect to be able to grasp completely in one hurried reading what other men learn only after many years of concentrated study.
But there is one part of astronomy in which the professional astronomer has little interest, and it is in this field that the interested amateur can become as proficient as the greatest of the ancient astronomers. This is the study of the apparent face of the sky, to the end of being able to identify the star groups or constellations, and to name many of the stars. One need not be a geologist to enjoy rolling hills or soaring mountains, or a botanist to enjoy a flower; to know and enjoy the stars requires no technical knowledge, but it is an achievement of which one may well be proud. It leads to greater appreciation of great works of music, art, and literature, for the heroes who fill the sky are favorites in these other aesthetic endeavors of mankind. Today most of us read very little of the old legends of Rome and Greece, but a study of the constellations will prove an incentive to greater enjoyment of these old stories.
The sky is parceled into named areas called constellations, as our country is divided into named areas called states. It is in just this way that a modern astronomer regards the constellations -- as named areas -- and it is quite likely that those forgotten stargazers who originally named the constellations thought of them in the same way. Sometime in between, however, there arose a demand that a constellation named Hercules, for example, should look like Hercules, the prodigiously strong son of Jupiter. Suppose we were to insist that a state named Washington should look like our first president! Or suppose the states of Georgia, North and South Carolina, Maryland and Virginia should have their boundaries changed, to force those states to be profile portraits of a King George, a King Charles, a Queen Mary, and a Queen Elizabeth (the Virgin) of England! We should regard such a thing as at least slightly silly, yet almost everyone is under the impression that the constellations are supposed to be pictures, because they bear the names of persons, creatures, and objects.
The earliest remaining complete description of the sky as seen from Greece was written by the poet Aratus, whom we shall mention again. He stated that certain mortals, "in ages long agone," finding that it was a tedious task and not particularly helpful in identification to give a name to every star, decided to name them in groups. Then, as we might refer to "that biggest oak tree in Johnson's meadow," the early watchers of the sky might speak of "the brightest star in the constellation Auriga." How soon after the naming process the pictures were associated with the constellations we do not know, but it must have been very early.
The earliest complete representation of the heavens as they were considered at the time appears to be the famous Farnese Globe, now in the Naples Museum. Discovered in Italy, it consists of white marble, and portrays Atlas on one knee, supporting on his bowed head and shoulders the celestial sphere, which he steadies with his hands. In an excellent state of preservation, it dates from at least as early as the first century before the Christian Era. Beautifully sculptured in raised relief, in the correct positions on the sphere, are the pictures of the constellations, but images of the stars are not shown.
Similarly, the earliest manuscript map of the sky contains only the constellation figures, and not the stars. The so-called Planisphere of Geruvigus, included in a Roman manuscript version of Aratus, dates from the second century A.D. and is now in the British Museum. It differs from the Farnese Globe and resembles modern maps in that it represents the actual face of the sky; that is, it shows the constellations as seen from the inside of the celestial sphere, as we see them from the earth.
In the earliest map showing the constellation figures and also the stars tolerably well located, we find a return to the practice of showing the sky as it appears on the surface of the sphere, as seen from the outside. It is the work of Peter Bienewitz (Latinized as Petrus Apianus), published as a single sheet, at Ingolstadt on August 5, 1536. It is a woodcut, well executed, representing forty-eight constellations.
But it was Johann Bayer, a lawyer and amateur astronomer of Augsburg, who published (1603) the star atlas which was the prototype of a number of fine atlases prepared by later astronomers. Bayer's Uranometria shows the positions of about 1250 stars, with their relative brightnesses quite accurately represented, and upon the star groups are shown the constellation pictures. The fifty-one plates were exquisitely engraved on copper by Alexander Mair. Here we find again a star map showing the sky as seen from the inside, as we actually see it, and practically every map of the sky (except, of course, celestial globes) has, since that time, been drawn this way. To Bayer, too, we owe our modern method of designating most of the naked-eye stars by letters of the Greek alphabet, in each constellation. His atlas passed through several editions.
It was more than a century before the star maps of Bayer were equaled, when John Flamsteed, the British Astronomer Royal, observed the positions of the stars for a catalogue and atlas (posthumously published in 1729). The constellation figures are in some respects superior to those of Bayer, without, perhaps, the same beautiful workmanship. There were many editions of this atlas, in which the practice of numbering the stars in each constellation, in order from west to east, was established. At a later moment, we shall explain and illustrate these designation schemes of Bayer and Flamsteed.
Later star atlases were published by Doppelmayer (1742), Bevis (1750), Burritt (1851) and others, but perhaps only that of Johann Elert Bode, about 1800, need be mentioned here. Bode seems to have been the first one to draw star charts to show the skies month by month, a scheme which has been quite popular for several generations, particularly for star maps intended for the beginner. It is a similar scheme which has been followed for the charts in this book.
Besides the sculptures and maps showing the pictures over the whole sky, there have come down to us descriptions of the sky and fragmentary representations which push yet farther back our knowledge of the framers of the constellations. Originally, modern astronomers believed that the Greeks had apportioned the sky into star groups, because most of the legends connected with the figures in the sky were known to be Greek. But, with the growth of our knowledge of the civilizations of the valley of the Tigris and Euphrates rivers, there has come a realization that many of the Greek myths had a Semitic origin. The Greeks simply changed the settings and the names, and took over the plots of the legends. Might they not similarly have taken over the constellations of the Euphratean peoples?
We know that the Akkadians and Sumerians, non-Semitic forerunners of the Babylonians, had names for many of the stars, chosen particularly from the words in use in shepherding. The stars were known as the "heavenly flock"; the bright star Arcturus was called Sibzianna, the "star of the shepherds of the heavenly herds." The sun was called the "old sheep"; the planets were the "old-sheep stars." This was the kind of astronomy inherited by the Babylonians from their predecessors in the Euphratean valley.
Examination of baked-clay tablets and cylinder seals which date from 3500 to 500 B.C. gives a few clues. One of the older myths describes a battle between Marduk, city-god of Babylon, and the dragon Tiamat. On a clay cylinder seal dating from at least as early as 3000 B.C., Izhdubar (better known in English literature as Gilgamesh) is pictured kneeling on a dragon. The Greeks inherited a constellation called En Gonasin, the Kneeler, who has one foot on the head of a dragon. They were reminded of their hero Herakles (Roman Hercules) and his struggle with the Dragon which guarded the Golden Apples of the Hesperides. So Hercules and Draco are surely two very old constellations. Another is Leo, the Lion, which is shown on an ancient clay tablet, with the star Regulus marking his heart. A cuneiform synthesis of all earlier inscriptions (known as the "Creation Legend," compiled about 650 B.C., during the reign of Assurbani-pal) indicates that there were recognized thirty-six constellations, divided into three groups -- northern, zodiacal, and southern.
The poems of Homer (Iliad and Odyssey, dating perhaps from the middle of the ninth century B.C., according to Herodotus) contain references to the constellations, but inasmuch as Homer was probably only the collector of the tales and ballads of earlier times, these constellations must be much older. The writings of Hesiod (Theogonia and Works and Days), about a century later, mention Arcturus, the Pleiades, the Hyades, Sirius and Orion, while Homer had referred to Ursa Major, in addition to these.
It is more than likely that the early Greeks received their astronomical lore from the Euphrateans, by way of the Phoenicians, a remarkable people who started out north of Palestine as early as 3000 B.C.; their great cities were Tyre and Sidon, but by 600 B.C. they had colonized North Africa and had founded the great city of Carthage, among others. Some of the best Greek astronomers (an instance is Thales of Miletus, about 600 B.C.) were of Phoenician descent.
Aglaosthenes (c. 650 B.C.) mentioned Aquila and Cynosura (now Ursa Minor). The early Mediterranean sailors had used what we call the Big Dipper in the northern heavens to guide them, but the Phoenicians switched to the Little Dipper, or Ursa Minor. Today we are alluding to this when we speak of something which is the center of attention as a cynosure.
Epimenides of Crete (c. 600 B.C.) wrote of Capricornus and the star Capella; Pherecydes of Athens (500-450 B.C.) told the legend of Orion and mentioned the fact that, as Orion sets, Scorpius rises; Aeschylus (526-456 B.C.) and Hellanicus of Mytilene (496-411 B.C.) tell the story of the seven Pleiades. Geminus of Rhodes relates that, in the fifth century B.C., Eustemon of Athens compiled a weather almanac in which he mentioned Orion, the Hyades, the Pleiades, Lyra, Cygnus, Aquarius, Corona, Delphinus, Pegasus, Aquila, and Canis Major as weather portents.
Eudoxus of Cnidus (c. 403-350 B.C.) appears to have been the earliest to write of constellations as such, merely for the purpose of writing a description of the sky. The title of his work was Phaenomena, and this title was preserved by the Cilician poet Aratus (c. 270 B.C.) when, by command of the Macedonian king Antigonus Gonatas, he put the description of the sky by Eudoxus into verse. The original work of Eudoxus has been lost.
Aratus begins with an invocation to the god Zeus and uses in the first words of the fifth verse the phrase, "For we are his children." Saint Paul, in his sermon to the Athenians (Acts 17:28), referring of course to the Supreme Being, quotes Aratus and one of his contemporaries, Cleanthes: "For in Him we live, and move, and have our being; as certain also of your own poets have said, For we are also his offspring."
In the Phaenomena of Aratus, forty-four constellations are named, but one of them is the small cluster we call the Pleiades and consider a part of Taurus. In addition, however, Procyon is mentioned, and this may be considered to be a recognition of Canis Minor as a separate named constellation. The star groups are placed in three regions: northern, zodiacal and southern. The zodiac, or "circle of animals," is that belt of the sky in which the sun, moon and bright planets are always to be found. Below is the list of the constellations named, described and located relatively to each other by Aratus. The Pleiades have been omitted, and Canis Minor has been put in place of Procyon. There remain two rather unfamiliar groups, Chelae and Serpentarius, and one whose name is not to be found in up-to-date lists: Argo Navis. We shall soon take care of these.
THE CONSTELLATIONS OF ARATUS
Ursa Major, Ursa Minor, Boötes, Draco, Cepheus, Cassiopeia, Andromeda, Perseus, Triangulum, Pegasus, Delphinus, Auriga, Hercules, Lyra, Cygnus, Aquila, Sagitta, Corona, Serpentarius
Aries, Taurus, Gemini, Cancer, Leo, Virgo, Chelae, Scorpius, Sagittarius, Capricornus, Aquarius, Pisces
Orion, Canis Major, Canis Minor, Eridanus, Lepus, Cetus, Argo Navis, Piscis Austrinus, Ara, Centaurus, Hydra, Crater, Corvus
Another who wrote a commentary on the Phaenomena of Eudoxus was Hipparchus of Bithynia, one of the greatest men of antiquity (c. 160-125 B.C.). His work in original form is not extant, but it was incorporated in a work of three centuries later, by Claudius Ptolemy. Hipparchus went further than mere description of the constellations in words; he compiled the first star catalogue, in which were listed the positions and the relative brightnesses of the stars. A century earlier, two Alexandrian astronomers, Aristillus and Timochares, had made measurements of star positions, and their work was adopted and extended by Hipparchus. It was he who inaugurated the classification of the stars by "magnitudes," the brightest stars being of the "first magnitude," the faintest visible to the naked eye being of the "sixth magnitude."
Callimachus and Eratosthenes, who were practically contemporary with Aratus, had written descriptions of the constellations, and in these a new constellation, Coma Berenices, had appeared, but Hipparchus and his successors for more than seventeen centuries seem to have overlooked it. It is recognized today as a full-fledged constellation. Hipparchus added two constellations by splitting Serpentarius into Ophiuchus and Serpens and by using some of the stars of Centaurus to form a new constellation, Lupus, the Wolf.
Hipparchus may also have been the one to introduce Equuleus and Corona Austrina, for we find them in the work of Claudius Ptolemy (c. 150 A.D.). This Alexandrian astronomer adopted practically without alteration the work of Hipparchus, and thus preserved it for us. But Ptolemy must have made some original observations, for the brightnesses of the stars are now set down as of a certain magnitude, or as a little brighter than, or a little fainter than, a certain magnitude.
For about seventeen centuries it was customary for astronomers to use the approximate brightnesses as given by Ptolemy. Then Sir William Herschel (1738-1822) and, in turn, his son Sir John (1792-1871) made extensive deep surveys of the sky, John even taking a sizable telescope to the Cape of Good Hope for a few years, to extend to the south celestial pole the work his father had done from England. These were statistical surveys, aimed at trying to discover the structure, dimensions and composition of the universe. The assumption had to be that, on the average, the stars are of the same intrinsic brightness and that their distances produce the differences in apparent brightnesses. It was essential, therefore, that the brightness scale be investigated.
About 1830, Sir John determined that the ancient magnitudes of Ptolemy were based on a geometrical, rather than an arithmetical, scale. That is, a star of magnitude 1.0 is a certain number of times as bright as a star of magnitude 2.0, which in turn is the same number of times as bright as a star of magnitude 3.0, and so on. This was verified by the physiologist Weber in 1834, and in 1859 the German psychologist G. T. Fechner put it into a general law or equation for all sensations, as Weber had suggested.
In 1856, the English astronomer N. R. Pogson carefully measured the brightnesses of many of the naked-eye stars and found that the average first-magnitude star of Hipparchus and Ptolemy was close to one hundred times as bright as the average sixth-magnitude star, so he established this as a convenient ratio; astronomers have followed it since, establishing standards and extending it to the faintest objects that can be seen or photographed through the largest telescopes.
A few stars are now considered brighter than the first magnitude, so they are called zero-magnitude stars; three are even brighter, so they have minus, or negative, magnitudes. Today, brightnesses are expressed even to the hundredth of a magnitude, although the eye can hardly distinguish differences of a tenth; magnitudes are continually being remeasured and refined with better equipment.
The scale is shown in the table of brightness ratios given here.
For values not in the table, we multiply the appropriate factors given. For example, a difference of 1.5 magnitudes is broken down into 1.0 and 0.5, and the ratios for these two are then multiplied: 2.512 times 1.585 equals 3.98, very nearly. A difference of 10 magnitudes is a ratio of 100 x 100, or 10,000 times in brightness.
The faintest stars observed today are of magnitude 23; Sirius, the brightest star in the sky, has an apparent visual magnitude of -1.42, or almost 24.5 magnitudes brighter than the faintest. We break this down into 5 + 5 + 5 + 5 + 4 + 0.5, and multiply the ratios. We get about 6,309,500,000, the ratio of the brightness of Sirius to that of the faintest observable star! The magnitude scale is a great boon to us, removing the necessity for using such huge numbers.
The sun's apparent magnitude is -26.8, almost 50 magnitudes brighter than the faintest observable stars, which means that the brightest object we see is almost 100,000,000,000,000,000,000 times as bright as the faintest one. It might be of interest to note that the star Sirius is just about one magnitude below the midpoint of this scale from the sun to the faintest observable star.
Now we must return to Ptolemy, who omitted the Coma Berenices group and listed a total of forty-eight constellations. But one of them included by Aratus had its name and significance changed. Chelae had become Libra.
In the Egyptian temple of Isis at Denderah, a circular representation of the heavens has been found. At first believed to be of great antiquity, it is now known to date only from the beginning of the Christian Era, in the reign of Caesar Augustus, although it may be a "corrupted" restoration of an earlier plaque, It is a strange mixture of independently conceived Egyptian constellations and conventional Greek figures. Aratus had described Chelae as the claws of Scorpius, but in this "Circular Zodiac of Denderah" this space is occupied by a pair of scales, or a balance, and so it has remained as the constellation Libra. In this transaction, the meaning of the word zodiac, the "circle of animals," has been violated, for a balance is not a living thing, however much its delicate trembling might make it seem alive. The two brightest stars of Libra bear names to remind us of their former affiliation. They are Zubenelgenubi and Zubeneschamali -- the southern and northern claws of the Scorpion.
More than fourteen centuries passed, after Ptolemy, before any new constellations were added. That any more were added at all may seem surprising, but it must be understood that the boundaries of the constellations had never been defined; the spaces between the named areas contained a few faint stars from which new constellations could yet be formed. Then, too, the Greeks could not see the many stars below their southern horizon, surrounding the south celestial pole, and the great age of exploration had to come before these stars could be observed and grouped in constellations, to complete the partition of the whole celestial sphere.
It was in Bayer's Uranometria (1603) that these southern stars were first shown and grouped into new constellations. From the Dutch navigator Pieter Dirchsz Keyser (or Petrus Theodori, as it was Latinized), who died in 1596, Bayer obtained a description of the sky which enabled him to fill in most of this southern part of the sphere with new constellations, some of which at least partially spilled over into the part of the sky known to the ancients but as yet unclaimed by any of the old classical constellations. The new groups are listed in the tables below.
BAYER'S NEW SOUTHERN CONSTELLATIONS
Apis (the Bee; now Musca, the Fly)
Avis Indica (Bird of Paradise; now Apus)
Chamaeleon (the Chameleon)
Dorado (commonly known as the Swordfish)
Grus (the long-necked bird, the Crane)
Hydrus (the Water Snake, not to be confused with the classical Hydra, the Water Serpent)
Indus (the American Indian)
Phoenix (the mythical bird, the Phoenix)
Piscis Volans (the Flying Fish; now simply Volans)
Tucana (the bird with the strange beak, the Toucan)
Triangulum Australe (the Southern Triangle)
Bayer omitted Coma Berenices, which had been revived by the Danish astronomer Tycho Brahe only a few years before the publication of the Uranometria, but practically all later astronomers included it. With Ptolemy's forty-eight constellations, Coma Berenices and the eleven new ones introduced by Bayer, the total became sixty.
Jacob Bartsch (c. 1599-1633), the son-in-law of the great German astronomer Johann Kepler (Tycho Brahe's greatest pupil and colleague), created three new constellations in areas in the north not claimed by others. They were Camelopardus (originally and sometimes today Camelopardalis, the Camelopard or Giraffe), Monoceros (the Unicorn) and Columba Noachi (the Dove of Noah; now simply Columba). Bartsch also stated that Isaak Habrecht, of Strassburg, had created another constellation in the south polar cap; it was Rhombus (lengthened by Lacaille to Reticulum Rhomboidalis, and now shortened to Reticulum, the Net). In 1679, Augustine Royer created Crux Australis (the Southern Cross; now Crux), which had been figured on earlier maps as a Cross, but had not yet been detached from Centaurus, whose hind legs it had formed. Our total, with these additions, stands at sixty-five constellations.
The Polish astronomer Hevelius of the city of Danzig published (posthumously, 1690) seven new groups, all in the north. They are as follows:
Canes Venatici (the Hunting Dogs)
Lacerta (the Lizard)
Leo Minor (the Lion Cub)
Lynx (the Lynx)
Sextans Uraniae (the Sextant of Urania; now simply Sextans)
Scutum Sobieskii (the Shield of John Sobieski, a Polish hero-king; now simply Scutum)
Vulpecula et Anser (the Fox and Goose; now simply Vulpecula)
Then Nicolas Louis de Lacaille (posthumously, 1769) introduced thirteen new constellations in the southern heavens; these are given in the list below. Lacaille took the stars of Pyxis from Argo Navis, one of the ancient constellations, and tried further to introduce a new constellation Malus (the Mast, of Argo Navis), but this did not survive. But because of the great size of the old constellation of Argo, modern astronomers have partitioned it into three new groups whose names are Carina (the Keel), Puppis (the Stern), and Vela (the Sail). Argo Navis is no more.
LACAILLE'S NEW SOUTHERN CONSTELLATIONS
Apparatus sculptoris (the Sculptor's Workshop; now simply Sculptor)
Fornax chemica (the Chemist's Furnace; now simply Fornax)
Horologium (the Clock)
Caela sculptoris (the Sculptor's Chisels; now simply Caelum)
Equuleus pictoris (the Painter's Easel; now simply Pictor)
Antlia pneumatica (the Air pump; now simply Antlia)
Octans (the navigation instrument invented by John Hadley)
Circinus (the Compasses)
Norma or Quadra Euclidis (the Carpenter's Square; now simply Norma)
Telescopium (the Telescope)
Microscopium (the Microscope)
Mons Mensae (the Table Mountain at Cape Town; now simply Mensa)
Pyxis nautica (the Mariner's Compass; now simply Pyxis)
The total number of constellations is now eighty-eight, and so it is likely to remain, for there is now no room for any more. In old atlases the constellation boundaries were drawn with an exceedingly great degree of freedom; from one author to another there were large differences. In 1928 a commission of the International Astronomical Union decided on definite boundaries for all the eighty-eight constellations, and astronomers will certainly adhere to these from now on. The complete modern list is given in the table.
Today the ancient figures are almost forgotten; the constellations are considered to be quite arbitrary areas of the sky, for the purpose of convenience only. As we can locate a city fairly accurately by naming the state in which it is found and describing its location within the state, so we can designate a star by describing its position within a constellation, or by adding something descriptive of its color or brightness.
In Bayer's Uranometria Greek letters were used to designate the individual stars in each constellation. For example, the star which the Arabs had indicated as Ibt-al-Jauza, the "Armpit of the Central One," and whose name had later been corrupted to Betelgeuse, was designated as alpha Orionis, or "alpha of Orion." The bright star Rigel, in the same constellation, was called ß Orionis (beta of Orion). In this scheme, the Latin genitive, or possessive, form of the constellation name might be considered the "family name" of the star, and a particular Greek letter the "given name." In general, the Greek letters were assigned in the order of the brightnesses of the stars in the constellation: alpha is the brightest, ß second brightest, gamma the third, and so on. There are, however, a number of exceptions. In some of these it can be seen that the order is the more or less random listing of Ptolemy. In the catalogue compiled by that writer from the work of Hipparchus and others, the stars in each constellation are grouped into classes of brightnesses, with no particular arrangement in each class. In Bayer's designations, a few exceptions to the current conventional order may be the result of actual changes in brightness since his day.
In Flamsteed's atlas of 1729, the stars are designated by numbers. A star which is westernmost in a given constellation is designated number 1; the one which is next most westerly is number 2; finally the easternmost star in the constellation bears the highest number. For example, the star Betelgeuse is 58 Orionis, because it lies well toward the east in the constellation, while Rigel, near the western edge of Orion, is 19 Orionis. This scheme, as well as that of Bayer, finds general acceptance and use today; in addition, we still use some of the Arabic proper names.
The gap of more than fourteen centuries between Ptolemy and Bayer was marked by little activity in astronomy in Europe, but the Arabs preserved Ptolemy's work and added a little to the progress of the subject. They were particularly active in the naming of individual stars. Most of the names are of Arabic origin, usually very bad corruptions of the original descriptions. Betelgeuse is a good example. For most of these names there are several variations. Only scholars of Arabic can advise us concerning the pronunciations of the uncorrupted names; someday we may be able to decide on the pronunciations of the others. Even for the purely Latin constellation names, there is no agreement as to pronunciation. In the body of the text describing each map, many star names are given, in addition to several included in the maps themselves.
MOTIONS IN THE SKY
Almost everyone knows that the earth rotates on its axis, and that due to this spinning we are carried eastward beneath the sun, thus causing the apparent motion of the sun across the sky each day. This must produce the same kind of apparent motion for any object, so the stars also appear to rise, arch across the sky, and set in the west.
If an observer were located precisely at the earth's north pole, the point exactly overhead -- the north celestial pole -- would appear to stand still, and all the stars would appear to describe circles about that point, each twenty-four hours. But we are about halfway from the north pole to the equator, so the north celestial pole stands about halfway up in the northern sky, instead of overhead. As the earth turns once each twenty-four hours, the stars all appear to move in circles about the north celestial pole as a center. The so-called North Star is quite close to the north pole of the sky, and we may regard this star as the center about which the sky turns each twenty-four hours.
However, in addition to the rotation on its axis, the earth has another very important motion; each year the earth makes one complete trip about the sun, in a path called its orbit. We see the sun in a different direction each day, because we stand in a different direction from the sun each day. Or we might think of it in this way: Suppose on one day the sun is in line with a certain star, as seen from the earth. On this day, the sun and the star will appear to rise together. On the next day, the earth will be a little farther along in its orbit, and the sun will appear to be a little to the east of the star. The star will rise first, and the sun will lag behind by almost four minutes. On the next day, the sun will lag almost eight minutes behind the star, and so on. Because the time we use is based upon the sun, and not upon the stars, we usually think of the stars as rising earlier each day, and slipping westward almost four minutes each day. In a month, this amounts to two hours, so each month we look for the same stars in the same places in the sky two hours earlier.
The North Star may be considered the center about which the stars describe the circles mentioned above. A star only a short distance from the North Star will trace out a small circle, one farther away will trace out a larger one, and so on. The small circles will be completely above the horizon; stars close to the North Star never set, while those far from it rise and set. There are, below our southern horizon, stars which never rise for us.
A study of the maps, in conjunction with what has been given in this section, may help the student to understand the behavior of the sky through the hours of the night and the days of the year.
THE SYNOPTIC TABLE
While each chart is marked for particular months and certain times, each chart can be used in another month at another time. Herewith is given a table to guide an observer in a selection of the correct chart for a given hour at a given time of year. For example, for July 16, from 8 to 10 P.M., the proper chart is No. 7; on the same night from 10 to 12, use chart No. 8. In the date column find the date which is nearest the exact date of observation; then look in the column headed by the time of observation. When a blank space is found, use the map indicated on either side of it.
Copyright © 1942, 1943, 1944, 1945, 1946, © 1964, 1974 by I. M. Levitt and Roy K. Marshall
Copyright © 1980, 1983, 1985, 1987, 1992 by I. M. Levitt
1964 Edition copyright renewed 1992