Page:A short history of astronomy(1898).djvu/57

From Wikisource
Jump to navigation Jump to search
This page has been validated.
§§ 12, 13]
The Constellations: the Zodiac
13

memory can follow them; bears, lions, and fishes, large and small, confuse all nomenclature." (Outlines of Astronomy, § 301.)

The constellations as we now have them are, with the exception of a certain number (chiefly in the southern skies) which have been added in modern times, substantially those which existed in early Greek astronomy; and such information as we possess of the Chaldaean and Egyptian constellations shews resemblances indicating that the Greeks borrowed some of them. The names, as far as they are not those of animals or common objects (Bear, Serpent, Lyre, etc.), are largely taken from characters in the Greek mythology (Hercules, Perseus, Orion, etc.). The constellation Berenice's Hair, named after an Egyptian queen of the 3rd century B.C., is one of the few which commemorate a historical personage.[1]

13. Among the constellations which first received names were those through which the sun passes in its annual circuit of the celestial sphere, that is those through which the ecliptic passes. The moon's monthly path is also a great circle, never differing very much from the ecliptic, and the paths of the planets (§ 14) are such that they also are never far from the ecliptic. Consequently the sun, the moon, and the five planets were always to be found within a region of the sky extending about 8° on each side of the ecliptic. This strip of the celestial sphere was called the zodiac, because the constellations in it were (with one exception) named after living things (Greek ζῷον, an animal); it was divided into twelve equal parts, the signs of the zodiac, through one of which the sun passed every month, so that the position of the sun at any time could be roughly described by stating in what "sign" it was. The stars in each "sign" were formed into a constellation, the "sign" and the constellation each receiving the same name. Thus

  1. I have made no attempt either here or elsewhere to describe the constellations and their positions, as I believe such verbal descriptions to be almost useless. For a beginner who wishes to become familiar with them the best plan is to get some better informed friend to point out a few of the more conspicuous ones, in different parts of the sky. Others can then be readily added by means of a star-atlas, or of the star-maps given in many textbooks.