Hesiod mentions Orion, the Pleiades, Sirius, Aldebaran, and Arcturus; and Homer refers to Orion, Arcturus, the Pleiades, the Hyades, the Great Bear (under the name of Amaxa, the Chariot), and the tail of the Little Bear, or “Cynosura.”
Hipparchus called the constellations Asterisms (ἀστερίσμος), Aristotle and Hyginus Σομάτα (bodies), and Ptolemy Σχημάτα (figures). By some they were called Μορφώσεις (configurations), and by others Μετεώρε. Proclus called those near the ecliptic Ζωδία (animals). Hence our modern name Zodiac.
Hipparchus, Ptolemy, and Al-Sufi referred the positions of the stars to the ecliptic. They are now referred to the equator. Aboul Hassan in the thirteenth century (1282) was the first to use Right Ascensions and Declinations instead of Longitudes and Latitudes. The ancient writers described the stars by their positions in the ancient figures. Thus they spoke of “the star in the head of Hercules,” “the bright star in the left foot of Orion” (Rigel); but Bayer in 1603 introduced the Greek letters to designate the brighter stars, and these are now universally used by astronomers. These letters being sometimes insufficient, Hevelius added numbers, but the numbers in Flamsteed’s Catalogue are now generally used.
Ptolemy and all the ancient writers described the constellation figures as they are seen on globes, that is from the outside. Bayer in his Atlas, published in 1603, reversed the figures to show them as they would be seen from the interior of a hollow globe and as, of course, they are seen in the sky. Hevelius again reversed Bayer’s figures to make them correspond with those of Ptolemy. According to Bayer’s arrangement, Betelgeuse (α Orionis) would be on the left shoulder of Orion, instead of the right shoulder according to Ptolemy and Al-Sufi, and Rigel (β Orionis) on the right foot (Bayer) instead of the left foot (Ptolemy). This change of position has led to some confusion; but at present the positions of the stars are indicated by their Right Ascensions and Declinations, without any reference to their positions in the ancient figures.
The classical constellations of Hipparchus and Ptolemy number forty-eight, and this is the number described by Al-Sufi in his “Description of the Fixed Stars” written in the tenth century A.D.
Firminicus gives the names of several constellations not mentioned by Ptolemy. M. Fréret thought that these were derived from the Egyptian sphere of Petosiris. Of these a Fox was placed north of the Scorpion; a constellation called Cynocephalus near the southern constellation of the Altar (Ara); and to the north of Pisces was placed a Stag. But all these have long since been discarded. Curious to say neither the Dragon nor Cepheus appears on the old Egyptian sphere.[389]
Other small constellations have also been formed by various astronomers from time to time, but these have disappeared from our modern star maps. The total number of constellations now recognized in both hemispheres amounts to eighty-four.
The first catalogue formed was nominally that of Eudoxus in the fourth century B.C. (about 370 B.C.). But this can hardly be dignified by the name of catalogue, as it contained only forty-seven stars, and it omits several of the brighter stars, notably Sirius! The first complete (or nearly complete) catalogue of stars visible to the naked eye was that of Hipparchus about 129 B.C. Ptolemy informs us that it was the sudden appearance of a bright new or “temporary star” in the year 134 B.C. in the constellation Scorpio which led Hipparchus to form his catalogue, and there seems to be no reason to doubt the accuracy of this statement, as the appearance of this star is recorded in the Chinese Annals. The Catalogue of Hipparchus contains only 1080 stars; but as many more are visible to the naked eye, Hipparchus must have omitted those which are not immediately connected with the old constellation figures of men and animals.
Hipparchus’ Catalogue was revised by Ptolemy in his famous work the Almagest. Ptolemy reduced the positions of the stars given by Hipparchus to the year 137 A.D.; but used a wrong value of the precession which only corresponded to about 50 A.D.; and he probably adopted the star magnitudes of Hipparchus without any revision. Indeed, it seems somewhat doubtful whether Ptolemy made any observations of the brightness of the stars himself. Ptolemy’s catalogue contains 1022 stars.
Prof. De Morgan speaks of Ptolemy as “a splendid mathematician and an indifferent observer”; and from my own examination of Al-Sufi’s work on the Fixed Stars, which was based on Ptolemy’s work, I think that De Morgan’s criticism is quite justified.