Origins & Early Life

Callippus (; Ancient Greek: Κάλλιππος, romanized: Kallippos; c. 370 BC – c. 300 BC) was a Greek astronomer and mathematician. Callippus was born at Cyzicus, and studied under Eudoxus of Cnidus at the Academy of Plato.

Pivotal Works & Achievements

He also worked with Aristotle at the Lyceum, which means that he was active in Athens prior to Aristotle's death in 322 BC. 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 27 spheres were insufficient to account for the planetary movements, and so he added seven more for a total of 34. According to the description in Aristotle's Metaphysics (XII.8), he added two spheres for the Sun, two for the Moon, and one each for Mercury, Venus, and Mars. Callippus made careful measurements of the lengths of the seasons, finding them (starting with the spring equinox) to be 94 days, 92 days, 89 days, and 90 days.

Enduring Legacy & Impact

This variation in the seasons implies a variation in the speed of the Sun, called the "solar anomaly". He also followed up on the work done by Meton of Athens to measure the length of the year and construct an accurate lunisolar calendar. The Metonic...

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