Eratosthenes, c.275-c.195 B.C., Greek scholar, b. Cyrene. A pupil of Callimachus in Athens, he became (c.240 B.C.) head of the library at Alexandria. Known for his versatility, he wrote poetry and works (most of them lost) on literature, the theater (notably on ancient comedy), mathematics, astronomy, geography, and philosophy; he also drew a map of the known world and evolved a system of chronology. Especially noted as an astronomer, he is credited with measuring the circumference and tilt of the earth and the size and distance from the earth of the sun and the moon.