Circa 190-120 B.C.E.
Astronomer And Geographer

Reputation. Like Eratosthenes, Hipparchus is quoted throughout Strabo's books. Hipparchus, who hailed from Nicaea (a city in Bithynia, in modern Turkey), flourished in the middle of the second century B.C.E, and is considered the greatest astronomer of antiquity. He discovered the precession of the equinoxes, accurately estimated the lunar distance, computed both lunar and solar eclipses, compiled the first catalogue of stars (containing a total of 850), and devised trigonometry. There is also reason to believe that he invented the plane astrolabe, which allowed a user to tell time at night from the stars' positions.

Revising Another's Work. Many of Hipparchus's writings were dedicated to advancing Eratosthenes' mathematical geography. No one can deny Eratosthenes' innovations or his contribution to geography, but subsequent authors such as Hipparchus aimed chiefly to create formulas that would improve Eratosthenes' measurements...