Eratosthenes (air-uh-ta-tha-knees)
Eratosthenes studied at Alexandria and some years in Athens. In 236 BC he was appointed by Ptolemy III Euergetes I as a head and the third librarian of the Alexandrian library. He made several important contributions to mathematics and science. He was a good friend to Archimedes. Circa 255 BC he invented the armillary sphere, which was used till 17th century.
He calculated the earth's circumference circa 240 BC, using trigonometry and information on the altitude of the Sun at noon in Alexandria and Syene (now Aswan, Egypt).
He calculated the earth's circumference circa 240 BC, using trigonometry and information on the altitude of the Sun at noon in Alexandria and Syene (now Aswan, Egypt).
