fl. 70 B.C.

Greek astronomer and mathematician who authored Introduction to Astronomy and Theory of Mathematics. The former is an elementary astronomy textbook based on the theories of Hipparchus (c. 170-c. 120 B.C.). The latter was more substantial, providing an exposition and classification of the principles of the mathematical sciences. In it, Geminus carefully defined mathematical terms and concepts including "hypothesis," "postulate," "axiom," "line," "surface," and "angle" as well as criticizing Euclid's (c. 330-c. 260 B.C.) parallel postulate.