Mathematician, Astronomer, Philosopher (c.370 BC – c.300 BC)

A lesser known astronomer compared to Aristarchus and Eratosthenes is Callippus of Cyzicus. His work in creating the Callippic Period or Callippic Cycle made the determination of the length of the solar year more accurate. It subsequently replaced the Metonic Cycle and was adopted by all later astronomers starting from as early as 330 BC.

He studied in Cyzicus. He was a student of Polemarchus and Eudoxus, both great astronomers, the later of whom he succeeded as director of the School of Cyzicus. According to Simplicius, Callippus settled in Athens where he worked close to Aristotle. The two collaborated in correcting and perfecting Eudoxus’ works.

Callippus is responsible for introducing thr Callippic Period, otherwise known as the Callippic Cycle in astronomy. Before him, Meton of Athens had calculated that one year is comprised of 365 days. The Metonic Cycle consisted of a 19-year period during which certain celestial phenomena such as lunar and solar eclipses repeated. This meant that Meton had estimated the year slighlty longer than it actually is. Callippus on the other hand gave a more precise estimation, determining that one year is comprised of 365,25 days. He noted that for a more accurate calculation of the duration of the year, the period should be four times that of the Metonic Cycle minus one day. This time period of 76 years came to be known as the Callippic Cycle.

Another important contribution to astronomy was the correction of Eudoxus’ system of homocentric spheres. Adding 7 more spheres, one to each planet, to Eudoxus’ proposed system increased the total number to 34. In this manner Callippus increased the accuracy of Eudoxus’ model and enabled a better understanding of the motion of the celestial spheres in the solar system. Furthermore, Callippus discovered that the duration of the seasons were not equal, rather: spring 94 days, summer 92 days, fall 89 days and winter 90. His discoveries were all written down in his books, none of which survive except from their titles.

Overall, Callippus’ discoveries contributed much to the development of astronomy, perhaps mostly for the future astronomers to make more accurate theories and estimations. Today a lunar crater is named in his honour.


  1. Chasapis, K.S. “Callippus”. Helios New Encyclopaedic Dictionary. Passas I. Athens: 1946. Print.
  2. Georgakopoulos, Konstantinos. Ancient Greek Scientists. Georgiades: Athens, 1996. Print.
  3. J.J. O’Connor, E.F. Robertson. Callippus of Cyzicus. School of Mathematics and Statistics, University of St. Andrew, Scotland. Web.

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