The 12 commonly accepted zodiac signs are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. These are constellations, or groups of stars, that ring the Earth and appear to be overhead during each successive month.
The zodiac constellations have been a part of culture since antiquity and persist today in horoscopes. Students of astrology or New Age traditions believe that the sign someone was born under – that is, the constellation that was overhead at the time of birth – confers different personality traits on a person. It also extends by grouping certain astrological signs as being romantically compatible with one another.
Each zodiac period starts on about the 20th of each month. For example, Aries starts around March 21 and lasts through April 19. The signs progress through the months until Pisces, which lasts from February 20 to March 20.
There are actually 13 zodiac constellations, but the final one, Ophiuchus, is usually not included in zodiac charts because it would supplant Scorpio's position. Due to the precession of the Earth, the zodiac signs have shifted about a month away from their positions at the time astrology was invented. Now, during the period of Capricorn, the sun actually appears in Sagittarius.