The New Student's Reference Work/Zodiac
Zo′diac, an imaginary zone of the heavens, within which lie the paths of the sun, moon and principal planets. It is bounded by two circles equidistant from the ecliptic — about 18° apart; is divided into 12 signs; and is marked by 12 constellations. The signs are geometrical divisions 30° in extent, counted from the vernal equinox in the direction of the sun’s progress through them. The whole series accordingly shifts westward through the effect of precession by about one degree in 72 years, requiring 25,868 years for a complete circuit. At the moment of crossing the equator toward the north the sun is said to be at the first point of Aries (Ram); some 30 days later it enters Taurus (Bull); and so on through Gemini (Twins), Cancer (Crab), Leo (Lion), Virgo (Virgin), Libra (Balance), Scorpio (Scorpion), Sagittarius (Archer), Capricornus (Goat), Aquarius (Water-Bearer) and Pisces (Fishes). The constellations bearing the same names coincided approximately in position when Hipparchus observed them at Rhodes, more than 2,000 years ago, with the positions they designate. The discrepancy now, however, amounts to the entire breadth of a sign, the sun’s path in Aries lying among the stars in Pisces; in Taurus among those of Aries; in Gemini among those of Taurus etc. This gradual retrogression of the signs through the constellations of the zodiac will continue till in about 25,868 years they accomplish a complete circuit. After this period the sign and constellation of Aries will coincide as they did in the time of Hipparchus.