Born in Tripolis, in Bithynia, Theodosius is cited by Vitruvius as having invented a sundial suitable for any place on Earth.
His Sphaerics provided the mathematics for spherical astronomy, and may have been based on a work by Eudoxus of Cnidus. Francesco Maurolico translated his works in the 16th century. In addition to the Sphaerics, two other works by Theodosius have survived: On Habitations, describing the appearances of the heavens at different climes, and On Days and Nights, a study of the apparent motion of the Sun.
- Ivor Bulmer-Thomas, "Theodosius of Bithynia," Dictionary of Scientific Biography 13:319–320.
- also on line  "Theodosius of Bithynia." Complete Dictionary of Scientific Biography. 2008. Encyclopedia.com. 25 Mar. 2015 .
- Chisholm, Hugh, ed. (1911). Encyclopædia Britannica. 26 (11th ed.). Cambridge University Press..