Most people have heard about the 12 signs of the zodiac, probably in relation to horoscopes and astrology. What people may not know is that the signs are changing – while you may have been an Aquarius before, you could be a Capricorn now. In fact, there is even a new zodiacal constellation, Ophiuchus, between Scorpio and Sagittarius. What are the origins of the zodiac and why are the signs different now?
Astronomers believe that the zodiac developed in ancient Egypt and was most likely adopted by the Babylonians. By studying the night sky, astrologers knew that the Sun took twelve lunar cycles (or months) to return to its original position. They also noticed certain constellations that correlated to the progression of the seasons. Ancient astrologers gave names to these 12 constellations based on when they occurred. There were four categories of signs: fire signs (Aries, Sagittarius, Leo), water signs (Cancer, Scorpio, Pisces), air signs (Libra, Aquarius, Gemini), and earth signs (Capricorn, Taurus, Virgo). For example, Aquarius is thus named because it was near the Sun during the Babylonian’s rainy season.
Some believe that the Babylonians purposefully left out a 13th constellation because they only wanted 12. In any case, there is a 13th zodiacal constellation, now called Ophiuchus, which occurs between Scorpio and Sagittarius. This means that there is a shift of dates, changing people’s zodiac sign. However, there is another reason why the dates of the zodiacal signs have changed: precession. Earth’s precession is the change in orientation of Earth’s rotational axis on a 26,000-year cycle. This causes the zodiacal signs to appear at different times of the year than they did when the zodiac was first created. It also means that at some point in the future, the zodiac signs will eventually appear in the sky at the same time they did for the Babylonians.
For more info on precession: Astronomy: precession of earth