Callippus

Callippus of Cyzicus (about 370 to about 300 BC) was a Greek astronomer and mathematician. Born at Cyzicus, he studied under Eudoxus of Cnidus at the Academy of Plato and also worked with Aristotle at the Lyceum in Athens. He tried to improve the scheme of connected spheres that Eudoxus used to account for the movements of the planets, finding twenty-seven spheres insufficient and adding seven more for a total of thirty-four. He measured the lengths of the four seasons, found them unequal, and so recognised that the Sun appears to move at a varying speed. He built on the work of Meton of Athens in measuring the length of the year, and the Callippic cycle of seventy-six years, equal to four Metonic cycles, bears his name; it was used by later astronomers and appears to be used in the Antikythera mechanism. A crater on the Moon is named after him.