Eratosthenes was born in Cirene, Libya, around 276 BC. He spent decades as the chief librarian and scholar at the Great Library of Alexandria.
Alexandria had, by then, taken over from Athens as the hub of intellectual endeavour in the Ancient World.
Eratosthenes is most famous for determining the astronomical parameters mentioned in the first paragraph. He is the first man known to have calculated these.
Eratosthenes also devised a calendar that included leap years. His writings include a poem inspired by astronomy, as well as works on the theatre and on ethics. Eratosthenes was afflicted by blindness in old age, and committed suicide by voluntary starvation.
The Eratosthenes biography ends with his death in 194 B.C. in Alexandria, Egypt .
Big Bang by Simon Singh contains a biography of Eratosthenes. It includes Eratosthenes' methods for calculating the circumference of the earth, diameter of the Moon, distance to the Moon, distance to the Sun, and diameter of the Sun.