In the first place we may notice that in the time of Hipparchus the vernal equinox was in the first degree of the Ram, from which our own arrangement has originated. Hipparchus lived 128 years B.C., or nearly 2,000 years ago, at which time the equinox was exactly at β Aries. Secondly, there are many reasons for believing that at the time of the invention of the zodiac, indeed in the first dawning of astronomy, the Bull was the first sign into which the sun entered at the vernal equinox. Now it takes 2,156 years to retrograde through a sign, and therefore the Bull might occupy this position any time between 2400 and 4456 B.C., and any nearer approximation must depend on our ability to fix on any particular part of the constellation as the original equinoctial point. We may say that whoever invented the zodiac would no doubt make this point the beginning of a sign, and therefore date its invention 2400 B.C.; or on the other hand, if it can be proved that the constellations were known and observed before this, we may have to put back the date to near the end of the sign, and make its last remarkable stars the equinoctial ones, say those in the horns of Taurus. Compare the line of Virgil,
"Candidus auratis aperit cum cornibus annum
Taurus."
The date in this case would be about 4500 B.C.—or once more some remarkable part of the constellation may give proof that its appearance with the sun commenced the year—and our date would be intermediate between these two. In fact, the remarkable group of stars known as the Pleiades actually does play this part. So much interest clusters, however, round this group, so much light is thrown by it on the past history of astronomical ideas—and so much new information has recently been obtained about it—that it requires a chapter to itself, and we shall therefore pass over its discussion here. Let us now review some of the indications that some part of the constellation of the Bull was originally the first sign of the zodiac.
We need perhaps only mention the astrological books of the Jews—the Cabal—in which the Bull is dealt with as the first zodiacal sign. Among the Persians, who designate the successive signs by the letters of the alphabet, A stands for Taurus, B for the Twins, and so on. The Chinese attribute the commencement of the sun's apparent motion to the stars of Taurus. In Thebes is a sepulchral chamber with zodiacal signs, and Taurus at the head of them. The zodiac of the pagoda of Elephanta (Salsette) commences with the same constellation.
However, reasons have been given for assigning to the zodiac a still earlier date than this would involve. Thus Laplace writes:—"The names of the constellations of the zodiac have not been given to them by chance—they embody the results of a large number of researches and of astronomical systems. Some of the names appear to have reference to the motion of the sun. The Crab, for instance, and the He-Goat, indicate its retrogression at the solstices. The Balance marks the equality of the days and nights at the equinoxes, and the other names seem to refer to agriculture and to the climate of the country in which the zodiac was invented. The He-Goat appears better placed at the highest point of the sun's course than the lowest. In this position, which it occupied fifteen thousand years ago, the Balance was at the vernal equinox, and the zodiacal constellations match well with the climate and agriculture of Egypt." If we examine this, however, we see that all that is probable in it is satisfied by the Ram being at the vernal, and the Balance at the autumnal equinox, which corresponds much better with other evidence.
The Zodiac of Denderah.
In the first instance, no doubt, the names of the zodiacal constellations would depend on the principal star or stars in each, and these stars and the portion of the ecliptic assigned to each may have been noticed before the stars round them were grouped into constellations with different names. In any case, the introduction of the zodiac into Greece seems to have been subsequent to that of the celestial sphere, and not to have taken place more than five or six centuries before our era. Eudemus, of Rhodes, one of the most distinguished of the pupils of Aristotle, and author of a History of Astronomy, attributes the introduction of the zodiac to Œnopides of Chio, a contemporary of Anaxagoras. They did not receive it complete, as at first it had only eleven constellations, one of them, the Scorpion, being afterwards divided, to complete the necessary number. Their zodiacal divisions too would have been more regular had they derived them directly from the East, and would not have stretched in some instances over 36° to 48°, like the Lion, the Bull, the Fishes, or the Virgin—while the Crab, the Ram, and the He-Goat, have only 19° to 23°. Nor would their constellations be disposed so irregularly, some to the north and some to the south of the ecliptic, nor some spreading out widely and others crammed close together, so that we see that they only borrowed the idea from the Easterns, and filled it out with their ancient constellations. Such is the opinion of Humboldt.
With regard to the origin of the names of the signs of the zodiac, we must remember that a certain portion of the zodiacal circle, and not any definite group of stars, forms each sign, and that the constellations may have been formed separately, and have received independent names, though afterwards receiving those of the sign in which they were. The only rational suggestion for the origin of the names is that they were connected with some events which took place, or some character of the sun's motion observed, when it was in each sign. Thus we have seen that the Balance may refer to equal nights and days (though only introduced among the Greeks in the time of Hipparchus), and the Crab to the retrogression or stopping of the sun at the solstice.
The various pursuits of husbandry, having all their necessary times, which in the primeval days were determined by the positions of the stars, would give rise to more important names. Thus the Ethiopian, at Thebes, would call the stars that by their rising at a particular time indicated the inundation, Aquarius, or the Waterer; those beneath which it was necessary to put the plough to the earth, the Bull stars. The Lion stars would be those at whose appearance this formidable animal, driven from the deserts by thirst, showed himself on the borders of the river. Those of the Ear of Corn, or the Virgin of harvest, those beneath which the harvest was to be gathered in; and the sign of the Goat, that in which the sun was when these animals were born.