Zodiac

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Zodiac, imaginary belt in the celestial sphere, extending about 8° on either side of the ecliptic, the apparent path of the Sun among the stars. The width of the zodiac was determined originally so as to include the orbits of the Sun and Moon and of the five planets (Mercury, Venus, Mars, Jupiter, and Saturn) that were known to the people of ancient times. The zodiac is divided into 12 sections of 30° each, which are called the signs of the zodiac. Starting with the vernal equinox and then proceeding eastward along the ecliptic, each of the divisions is named for the constellation situated within its limits in the 2nd century bc. The names of the zodiacal signs are Aries, the Ram; Taurus, the Bull; Gemini, the Twins; Cancer, the Crab; Leo, the Lion; Virgo, the Virgin; Libra, the Balance; Scorpio, the Scorpion; Sagittarius, the Archer; Capricorn, the Goat; Aquarius, the Water Bearer; and Pisces, the Fishes. Because of the precession of the equinoxes about the ecliptic, a 26,000-year cycle, the first point of Aries retrogrades about 1° in 70 years, so that the sign Aries today lies in the constellation Pisces. In about 24,000 years, when the retrogression will have completed the entire circuit of 360°, the zodiacal signs and constellations will again coincide.

It is believed that the zodiacal signs originated in Mesopotamia as early as 2000 bc. The Greeks adopted the symbols from the Babylonians and passed them on to the other ancient civilizations. The Egyptians assigned other names and symbols to the zodiacal divisions. The Chinese also adopted the 12-fold division, but called the signs rat, ox, tiger, hare, dragon, serpent, horse, sheep, monkey, hen, dog, and pig. Independently, the Aztec people devised a similar system.

See also Astrology.

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