Geminus

Geminus was a Stoic philosopher and writer on astronomy and mathematics who worked in the Greek world, most likely at Rhodes, which was then the centre of astronomical research. Despite his Latin name he was thoroughly Greek. His dates are uncertain: some historians place him in the first century before the common era as a pupil or follower of Posidonius, while Otto Neugebauer argued from the Egyptian Isis festival calendar in his text that it was written around 50 CE. His surviving work is the Isagoge, or Introduction to Astronomy, an elementary text based on Hipparchus that describes the constellations, the length of day and night at different latitudes, the zodiac, the lunar month, the phases of the Moon, eclipses and planetary motion, and gives a history of earlier astronomical theories including those of Callippus and the Chaldeans. Its last chapter is more technical and uses mean motion to represent the moon in longitude. His Theory of Mathematics is lost, but Proclus quotes it at length and relied on it for his own history of mathematics. Geminus also attempted to prove Euclid's parallel postulate from the other axioms.