Zodiac, an imaginary belt in the sky extending some 8 on either side of the ecliptic, the apparent annual path of the sun among the stars. The moon and the planets (with the exception of Pluto) appear to follow paths within this belt. The zodiac is evenly divided into 12 areas, or signs, which play an important role in astrology.

The signs of the zodiac are named after the constellations, or groups of stars, that lie along the zodiac as recorded by the ancient Greeks more than 2,000 years ago. (The word "zodiac" is from the Greek word for "animal," a reference to the many constellations along the zodiac representing animals.) Today, the signs of the zodiac and the constellations for which they are named no longer coincide because the position of the constellations in the sky is slowly shifting For example, at the beginning of spring, the sun enters the sign called Aries, but the sun does not enter the constellation Aries until about a month later. This shift, called the precession of the equinoxes, is caused by a wobble of the earth's axis of rotation. In addition, the signs and constellations do not coincide because the constellation boundaries recognized by astronomers today are unevenly spaced and the sun spends much more time in some constellations than in others.