Eratosthenes

Who is Eratosthenes?

Eratosthenes of Cyrene was a Greek polymath born in the ancient city of Cyrene, in the region of modern-day Shahhat, Libya, then a prosperous Greek colony renowned for its schools of philosophy and rhetoric. After studying in Athens, he was invited to Alexandria around 245 BC by King Ptolemy III and eventually appointed chief librarian of the great Library of Alexandria, one of the ancient world's foremost centers of learning. Eratosthenes worked across an unusually wide range of fields, including geography, mathematics, astronomy, music theory, and poetry, and is credited with coining the word 'geography' itself. He is best remembered for calculating the circumference of the Earth with remarkable accuracy for his era, using the differing angles of the sun's shadow at Alexandria and Syene (modern Aswan) on the summer solstice, arriving at a figure within a few percent of the modern measurement. He also devised the 'Sieve of Eratosthenes,' a method still taught today for identifying prime numbers, and produced some of the earliest known maps of the known world complete with a system of latitude and longitude lines. His work laid foundations for scientific geography and mathematics that influenced scholars for centuries afterward.

Sources: Wikipedia, "Eratosthenes" · Britannica, "Eratosthenes" · Linda Hall Library, "Eratosthenes of Cyrene"