c. 160-c. 90 B.C.

Greek mathematician and astronomer whose surviving works include the Sphaerics. Intended to provide a mathematical grounding for astronomy, the Sphaerics expands on the Elements of Euclid (c. 325-c. 250 B.C.) with regard to spheres. In On Habitations, Theodosius discussed the view of the universe due to Earth's rotation, and in On Days and Nights he examined rules governing the length of day and night as a function of location and season.