The Zodiac is an astronomical division of the sky through which the apparent paths of the sun, moon, and major planets all pass. The zodiac is considered to have 12 segments, each covering 30°, and each of which is named for a constellation, groups of stars that have acquired names in the Greco-Roman tradition, often of animals and mythological characters. Note that there are other cultural traditions of constellations that are not part of this system. For example, there are Native American, African, Hawaiian, Australian aborigine, and Arab constellations.

The measurements of the zodiac were originally taken from the point of the vernal equinox, but because of the movement of the vernal equinox along the ecliptic, the constellations of the zodiac no longer correspond properly to the 30° segments. Zodiac comes from the Greek root meaning "animal," and many of the zodiac constellations are considered to represent animals. Beginning from the vernal equinox as it was first set, this is the zodiac order:

Astrological traditions, which study the celestial bodies and their influence on human lives, also make use of the zodiac system. In western astrology, signs are used to interpret an astrological chart that is often based on the time and place of the event being charted, often a person’s moment of birth. Zodiac symbols are also commonly seen on horoscopes found in daily newspapers and on the Internet. Unlike astrological charts, newspaper horoscopes are based on the month of birth only. Each sign is considered to have general characteristics shared by all people born in the month of that sign.

There are sets of signs associated with each of the four classical elements of earth, air, fire, and water. Cancer, Scorpio, and Pisces are said to be water signs. Aries, Leo, and Sagittarius are called the fire signs. Gemini, Libra, and Aquarius are considered to be air signs. Taurus, Virgo, and Capricorn are classified as the earth signs.