The symbol of Gemini is twins, which are traditionally presented in many different forms. So although astrology, which looks for answers, signs and predictions in the movements of celestial bodies, is not itself a science, there is a long history of people looking at the stars to plan their lives. Farmers used the sky as a calendar as long ago as the ancient Egyptians, when the rise of Sirius, the Dog Star, was seen in mid-July as a marker of the impending annual flooding of the Nile.
These dates are still used for astrological signs, although the precession of the equinoxes has shifted the constellations to the east; for example, on January 1, the direction of the sun is now in Sagittarius instead of Capricorn. The history of symbols is unknown; they seem to appear for the first time in Greek manuscripts from the late Middle Ages. In physics, precession is described as the change in the orientation of an axis of rotation.
In Chinese astrology, the zodiac of twelve animal signs represents twelve different types of personality. The zodiac traditionally begins with the sign of the Rat, and there are many stories about the origin of the Chinese zodiac that explain why this is so. When the twelve signs of the zodiac are part of the 60-year calendar in combination with the four elements, they are traditionally called astrology the twelve earthly branches. The Chinese zodiac follows the Chinese lunisolar calendar and therefore the days of “change” in a month vary each year. The following table shows the estimated dates of the twelve astrological signs, along with the classical and modern rules of each sign. Aries, by definition, begins at the First Point of Aries, which is the location of the Sun at the March equinox.
A birth star chart therefore presents the sky at the exact date and time of birth, from which the astrologer extrapolates character traits and predictions. The dates of the constellations are now about a month earlier when the Sun meets the corresponding constellations. These dates were established more than two thousand years ago, but today things have changed. For example, Aries now meets the Sun around April 19 instead of the astrological date of March 21. So most people who consider themselves Aries were born when the Sun was in Pisces.
Travelers used the sky as a compass and followed the stars to know where to go. Hellenistic astrology is partly derived from Babylonian and Egyptian astrology. 50 BC, is the first known representation of the classical zodiac of twelve signs. In Babylonian astronomical journals, a planetary position was usually given with respect to a constellation alone, less often in specific degrees within a sign.