The zodiac is split into twelve signs in Western astrology, and historically astronomy, each encompassing 30 degrees of celestial longitude and generally correlates to the constellations: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces. The modern system dates from about 300 B.C.; before then, different systems were used.
There are other systems in use as well, such as Chinese astrology which uses the same terms but groups the signs together in terms of their associated elements (fire, earth, air, water).
Some authors claim that there are 13 signs in a zodiacal chart, but this seems to be based on a misinterpretation of certain rules regarding how to read a chart. In fact, there are 12 distinct signs that can be counted on one hand; perhaps this explains why there are so many movies and books with characters who are "zodiac-born".
Astrologers usually refer to the signs as individually representing some aspect of human behavior or experience. For example, Aries is said to represent a warrior, Taurus a farmer, Gemini a trader, etc. However, it is not exactly correct to say that all people born under the sign of Aries will act like warriors, or that all people born under the sign of Pisces will act like fish.
The yearly passage of the sun across our sky defines it. The Zodiac, or the 12 signs of the zodiac stated in a horoscope, is intimately related to how the Earth travels through the skies. The signs are drawn from the constellations that outline the journey the sun seems to take over the course of a year.
There are also theories about what might have caused the zodiac to emerge. Some say it was based on observations made by ancient astronomers while others claim it is derived from constellations visible from certain parts of the world. Whatever its origin may be, it is widely accepted that the signs now define characteristics about which there is some degree of agreement among most cultures throughout history.
Each sign of the zodiac is associated with a different personality trait and celestial body. They form a framework within which people can be classified according to their traits and behaviors. The zodiac has had an enormous influence on many cultures throughout history and continues to do so today.
In modern times, psychologists use the zodiac as a reference point for classifying personalities. Each sign represents a different psychological type: Aries (March 21-April 19), for example, is said to be "the pioneer type" who likes to lead and try new things. Taurus (April 20-May 20) is described as "the guardian type" who is stable and reliable.
Astrological signs are the twelve 30 degree sectors that make up Earth's 360 degree orbit around the Sun in Western astrology. Each sign was named after a constellation that the sun passed through on its yearly journey across the sky. This finding is underlined in the popular and simplified sun sign astrology.
In ancient Greece, the constellations were first identified by Callisto (who was turned into a bear because she offended Hera) and Hippomenes (who identified the remaining ones). They are also listed in the Herbal of Pseudo-Apulian Medicine as Aratus. The identification of the signs with constellations was probably not intended by the astronomers who invented them. It is only much later that this connection was made.
Today, we know the zodiac as the circle of 12 constellations into which the Earth orbits every year. These constellations were originally identified by Eratosthenes about 275 BC. According to myth, he was studying the size of the Earth when he realized that some cities on the same meridian were closer together than others. He concluded that these differences had to be due to variation in latitude and therefore created a system of coordinates based on this discovery. Later scholars recognized that these differences could be attributed to the fact that some cities lie within certain constellations while others do not.