Callippus

Greek astronomer

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June 22, 2026

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Callippus was a Greek astronomer who lived around the 4th century BCE. He was a student of Eudoxus of Cnidus and made improvements to his teacher's model of celestial motion. Eudoxus's theory of homocentric spheres, which described celestial bodies as being carried on concentric spheres, was modified by Callippus to better account for planetary movements, particularly for Mercury and Venus. While Eudoxus's model was influential in cosmology, it failed to explain observed brightness changes in planets, suggesting their distances from Earth varied. Callippus's refinements were part of the ongoing effort in ancient Greek astronomy to "save the phenomena" by creating mathematical models that could predict celestial movements using uniform circular motion.12

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calendar
Complex cycles
…cycle was improved by both Callippus and Hipparchus. Callippus of Cyzicus (c. 370–300 bce) was perhaps the foremost astronomer of his day. He formed what has been called the Callippic period, essentially a cycle of four Metonic periods. It was more accurate than the original Metonic cycle and made use…
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…cycle was improved by both Callippus and Hipparchus. Callippus of Cyzicus (c. 370–300 bce) was perhaps the foremost astronomer of his day. He formed what has been called the Callippic period, essentially a cycle of four Metonic periods. It was more accurate than the original Metonic cycle and made use…
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physical science
Ancient Middle Eastern and Greek astronomy
The system was modified by Callippus, a student of Eudoxus, who added spheres to improve the theory, especially for Mercury and Venus. Aristotle, in formulating his cosmology, adopted Eudoxus’s homocentric spheres as the actual machinery of the heavens. The Aristotelian cosmos was like an onion consisting of a series of…
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The system was modified by Callippus, a student of Eudoxus, who added spheres to improve the theory, especially for Mercury and Venus. Aristotle, in formulating his cosmology, adopted Eudoxus’s homocentric spheres as the actual machinery of the heavens. The Aristotelian cosmos was like an onion consisting of a series of…
Read More