SHEILA TERRY / SCIENCE PHOTO LIBRARY SHEILA TERRY / SCIENCE PHOTO LIBRARY
Traditional portrait of Eratosthenes (c 276-195 BC). He was a Greek mathematician, astronomer, and geographer. Born in Cyrene, (now in Libya) he lived and worked in Alexandria, where he was appointed librarian of the great Library by Ptolemy lll. Amongst his many achievements he was the first to calculate the circumference of the Earth (c 240BC) achieving an accuracy of better than 2 per cent. He also computed the distances of the Earth from the Moon and the Sun and he accurately measured the angle of the ecliptic. His system of calculating prime numbers is known as âEratosthenes' Sieveâ. He established the discipline of geography, developed a system of latitude and longitude, produced a map of the known world.
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