The Mayan calendar ends on Dec. 21, 2012 (approximately when converted to the gregorian calendar). The Mayans had a very accurate calendar, tracking movements of the sun, moon and several stars and planets. This is how they kept time and track of days and years. The calendar advances all the way to Dec 21, 2012 and suddenly stops at this point. There have been theories that this is a prophecy of doomsday, however it is more likley that the calendar ended on this date due to it being on a solstice (one theory).
