- G. J. Toomer
Callippus (RE 22), astronomer (fl. 330 BCE), went with Polemarchus (pupil of *Eudoxus (1)) from *Cyzicus to Athens, where he associated with Aristotle. He corrected Eudoxus’ theory of concentric spheres (Simplic. in Cael. 493, 5–8), by adding two more spheres in each case for the sun and moon, and one more for each of the planets (see Arist. Metaph. 1073b 32–8; Simplic. inCael. 497, 17–24). He proposed a year-length of 365¼ days, on which he based the 76-year cycle named after him, containing 27,759 days and 940 months (of which 28 were intercalary), as an improvement on *Meton's 19-year cycle (Geminus 8. 57–60); the first ‘Callippic Cycle’ began in 330–329 bce. Callippus also composed the first parapēgma (astronomical calendar) to demonstrate clearly the inequality of the seasons.
- Science, Technology, and Medicine