There are 12 zodiac signs in the Western system, one for each 30 degrees of the celestial sphere. Each sign reigns over about a month of time, with the ruling sign determined by which zodiac constellation the sun appears to be in at a given time.
The Western system is shared by Europe and the Middle East, but other cultures developed their own systems. The Mayan zodiac, also used by the Aztec and Inca people, had 20 signs. The Chinese zodiac boasted a total of 28 lunar signs and 12 annual signs. However, the Western zodiac was exported to China around the 17th century, and their lunar system has fallen mostly into disuse.