The zodiac (literally, "circle of animals," or, in its more primary meaning, the "circle of life" or "circle of living beings") is the "belt" constituted by the 12 signs—Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces. This belt is said to extend 8° or 9° on either side of the ecliptic (the imaginary line drawn against the backdrop of the stars by the orbit of Earth). The orbits of the various planets in the solar system all lie within approximately the same geometric plane, so from a position within the system, all the heavenly bodies appear to move across the face of the same set of constellations. Several thousand years ago, the names of these constellations became the basis for the zodiac.
A distinction must be drawn between the sidereal zodiac and the tropical zodiac. The sidereal zodiac is located more or less where the constellations are positioned. The other zodiac originated with Ptolemy, the great astrologer-astronomer of antiquity, who was very careful to assert that the zodiac should begin (i.e., 0° Aries should be placed) at the point where the Sun is positioned during the spring equinox. Because of the phenomenon known as the precession of equinoxes, this point very gradually moves backward every year, and currently 0° Aries is located near the beginning of the constellation Pisces. Astrologers who adhere to the Ptolemaic directive—the great majority of modern, Western astrologers—use the tropical zodiac (also called the moving zodiac, for obvious reasons). If the tropical zodiac is used, it should always be carefully distinguished from the circle of constellations (i.e., from the sidereal zodiac).
The notion of the zodiac is ancient, with roots in the early cultures of Mesopotamia; the first 12-sign zodiacs were named after the gods of these cultures. The Greeks adopted astrology from the Babylonians; the Romans, in turn, adopted astrology from the Greeks. These peoples renamed the signs of the Babylonian zodiac in terms of their own mythologies, which is why the familiar zodiac of the contemporary West bears names out of Mediterranean mythology. The notion of a 12-fold division derives from the lunar cycle (the orbital cycle of the Moon around Earth), which the Moon completes 12 times per year.
From a broad historical perspective, zodiacal symbolism can be found everywhere, and zodiacal expressions are still in use in modern English—e.g., bullheaded (an
allusion to Taurus), crabby (an allusion to Cancer), etc. Throughout the centuries people have drawn parallels between the zodiac and many other 12-fold divisions—such as the Twelve Labors of Hercules, the Twelve Disciples, and the Twelve Tribes of Israel. The popularity of sun-sign astrology (the kind found in the daily newspaper) has kept these ancient symbols alive in modern society, and even such prominent artifacts as automobiles have been named after some of the signs (e.g., the Taurus and the Scorpio).
Cirlot, Juan Eduardo. A Dictionary of Symbols. London: Routledge & Kegan Paul, 1971. Gettings, Fred. Dictionary of Astrology. London: Routledge & Kegan Paul, 1985. Tester, Jim. A History of Western Astrology. New York: Ballantine, 1987.
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