Deriving from Mayan Astrology, the Mayan Zodiac has 20 “day signs.” The calendar is 260 days divided into groups of 20 days. Each group has a “sign.” The calendar is referred to as the Tzolkin Calendar. Mayans were among the first ancient peoples to study the bodies that they observed in the sky. The Mayans did not invent the calendar ... other tribes of indigenous peoples from Central American did so ... but they improved the calendar. The calendar is still used today by some Mayan tribes.