The zodiac signs are a series of 12 constellations that the sun appears to pass through over the course of a year. In order, they are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. Each of the signs has a meaning, according to astrological belief.
There are actually 13 zodiac constellations, but the sign after Scorpio, Ophiuchus, is not considered to be part of the traditional zodiac. Each of the zodiac signs is located around the ecliptic of Earth's orbit, so the sun appears to pass through them as the Earth revolves around the sun. Being born "under" one of the signs is said to influence different personality traits on the individual, and different signs are romantically compatible. For example, people born under Aries are said to be headstrong, while Pisces are considered to be creative.
Each astrological sign is dominant for about a month, as the Earth and sun move into the next sign. However, the axis of Earth slowly turns over a period of 24,000 years. This causes the zodiac signs to shift relative to Earth. Therefore, they are not in the sky at the same time as they were 2,000 years ago. Each sign has shifted about a month since that time.