ERATOSTHENES

Eratosthenes (276-194 BC) was a Greek mathematician, geographer and astronomer. He was born in Cyrene, Libya, and lived in Alexandria, Egypt, where King Ptolemy III appointed him head of the Library of Alexandria. His most celebrated scientific achievement was the measurement of the circumference of the Earth. In an ingenuous experiment that is re-enacted by students worldwide every year, he estimated it at 252,000 stadia, off the actual value (40,075 km) by just -2.4% or +0.8%, depending on the stadion unit used (155-160 m). He also calculated the distance from the Earth to the Moon and to the Sun, again achieving close approximations. Eratosthenes was the founder of scientific chronology, starting from the Trojan War, in his Chronographies and Olympic Victors. Other major works included his Geographica – he is actually credited with coining the term “geography” – and Catasterismi (on constellations).