
Callippus (or Calippus) (circa 370 B.C.–circa 300 B.C.) was a Greek astronomer. He was born at Cyzicus, and studied under Eudoxus. He observed the movements of the planets and attempted to use Eudoxus' scheme of connected spheres to account for their movements. However he found that 26 spheres was insufficient to account for the planetary movements, and so he added eight more for a total of 34. He also made careful measurements of the lengths of the seasons, and used this to build a 76year cycle to synchronize the lunar and solar years. This was adopted in 330 BC and subsequently used by later astronomers. on the Moon is named for him.

