Part 15 (1/2)
Historical
The grouping of the stars into constellations is of great antiquity. The exact date of their formation is not exactly known, but an approximate result may be arrived at from the following considerations. On the celestial spheres, or ”globes,” used by the ancient astronomers, a portion of the southern heavens of a roughly circular form surrounding the South Pole was left blank. This s.p.a.ce presumably contained the stars in the southern hemisphere which they could not see from their northern stations.
Now, the centre of this circular blank s.p.a.ce most probably coincided with the South Pole of the heavens at the time when the constellations were first formed. Owing to the ”Precession of the Equinoxes” this centre has now moved away from the South Pole to a considerable distance. It can be easily computed at what period this centre coincided with the South Pole, and calculations show that this was the case about 2700 B.C. The position of this circle also indicates that the constellations were formed at a place between 36 and 40 north lat.i.tude, and therefore probably somewhere in Asia Minor north of Mesopotamia. Again, the most ancient observations refer to Taurus as the equinoxial constellation. Virgil says--
”Candidus auratis aperit c.u.m cornibus annum Taurus.”[382]
This would indicate a date about 3000 B.C. There is no tradition, however, that the constellation Gemini was ever _seen_ to occupy this position, so that 3000 B.C. seems to be the earliest date admissible.[383]
Prof. Sayce thinks that the ”signs of the Zodiac” had their origin in the plains of Mesopotamia in the twentieth or twenty-third century B.C., and Brown gives the probable date as 2084 B.C.[384]
According to Seneca, the study of astronomy among the Greeks dates back to about 1400 B.C.; and the ancient constellations were already cla.s.sical in the time of Eudoxus in the fourth century B.C. Eudoxus (408-355 B.C.) observed the positions of forty-seven stars visible in Greece, thus forming the most ancient star catalogue which has been preserved. He was a son of Eschinus, and a pupil of Archytas and probably Plato.
The work of Eudoxus was put into verse by the poet Aratus (third century B.C.). This poem describes all the old constellations now known, except Libra, the Balance, which was at that time included in the Claws of the Scorpion. About B.C. 50, the Romans changed the Claws, or Chelae, into Libra. Curious to say, Aratus states that the constellation Lyra contained no bright star![385] Whereas its princ.i.p.al star, Vega, is now one of the brightest stars in the heavens!
With reference to the origin of the constellations, Aratus says--
”Some men of yore A nomenclature thought of and devised And forms sufficient found.”
This shows that even in the time of Aratus the constellations were of great antiquity.
Brown says--
”Writers have often told us, speaking only from the depths of their ignorance, how 'Chaldean' shepherds were wont to gaze at the brilliant nocturnal sky, and to _imagine_ that such and such stars resemble this or that figure. But all this is merely the old effort to make capital out of nescience, and the stars are before our eyes to prove the contrary. Having already certain fixed ideas and figures in his mind, the constellation-former, when he came to his task, applied his figures to the stars and the stars to his figures as harmoniously as possible.”[386] ”Thus _e.g._ he arranged the stars of _Andromeda_ into the representation of a chained lady, not because they naturally reminded him (or anybody else) of such a figure, but because he desired to express that idea.”
A coin of Manius Aquillus, B.C. 94, shows four stars in Aquila, and seems to be the oldest representation extant of a star group. On a coin of B.C.
43, Dr. Vencontre found five stars, one of which was much larger than the others, and concludes that it represents the Hyades (in Taurus). He attributes the coin to P. Clodius Turrinus, who probably used the constellation Taurus or Taurinus as a phonetic reference to his surname. A coin struck by L. Lucretius Trio in 74 B.C., shows the seven stars of the Plough, or as the ancients called them Septem Triones. Here we have an allusion to the name of the magistrate Trio.[387]
In a work published in Berne in 1760, Schmidt contends that the ancient Egyptians gave to the constellations of the Zodiac the names of their divinities, and expressed them by the signs which were used in their hieroglyphics.[388]
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 (aste??s??), Aristotle and Hyginus S?ata (bodies), and Ptolemy S??ata (figures). By some they were called ???f?se?? (configurations), and by others ?ete??e. Proclus called those near the ecliptic ??d?a (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 Ha.s.san in the thirteenth century (1282) was the first to use Right Ascensions and Declinations instead of Longitudes and Lat.i.tudes. 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 (a Orionis) would be on the left shoulder of Orion, instead of the right shoulder according to Ptolemy and Al-Sufi, and Rigel ( 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 cla.s.sical 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. Freret 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.
Al-Sufi's _Description of the Fixed Stars_ was written in the tenth century and contains 1018 stars. He seems to have adopted the _positions_ of the stars given by Ptolemy, merely correcting them for the effects of precession; but he made a very careful revision of the star magnitudes of Ptolemy (or Hipparchus) from his own observations, and this renders his work the most valuable, from this point of view, of all the ancient catalogues.
Very little is known about Al-Sufi's life, and the few details we have are chiefly derived from the works of the historians Abu'-l-faradji and Casiri, and the Oriental writers Hyde, Caussin, Sedillot, etc. Al-Sufi's complete name was Abd-al-Rahman Bin Umar Bin Muhammad Bin Sahl Abu'l-husan al-Sufi al-Razi. The name Sufi indicates that he belonged to the sect of Sufis (Dervishes), and the name Razi that he lived in the town of Ra in Persia, to the east of Teheran. He was born on December 7, 903 A.D., and died on May 25, 986, so that, like many other astronomers, he lived to a good old age. According to ancient authorities, Al-Sufi--as he is usually called--was a very learned man, who lived at the courts of Schiraz and Baghdad under Adhad-al-Davlat--of the dynasty of the Budes--who was then the ruler of Persia. Al-Sufi was held in high esteem and great favour by this prince, who said of him, ”Abd-al-Rahman al-Sufi taught me to know the names and positions of the fixed stars, Scharif Ibn al-Aalam the use of astronomical tables, and Abu Ali al-Farisi instructed me in the principles of grammar.” Prince Adhad-al-Davlat died on March 26, 983. According to Caussin, Al-Sufi also wrote a book on astrology, and a work ent.i.tled _Al-Ardjouze_, which seems to have been written in verse, but its subject is unknown. He also seems to have determined the exact length of the year, and to have undertaken geodetic measurements. The al-Aalam mentioned above was also an able astronomer, and in addition to numerous observations made at Baghdad, he determined with great care the precession of the equinoxes. He found the annual constant of precession to be 51”4, a value which differs but little from modern results.