ASTR 100 Lecture Notes - Lecture 7: Ptolemy Iii Euergetes, Geocentric Model, Heliocentrism
30 Jul 2017
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Document Summary
Eratosthenes was the third librarian of alexandria under ptolemy iii in the hellenistic period of. Ancient greece following the conquests of alexander the great. In around 240 bc, he was tasked with measuring the earth as one of the few educated people in greece at the time. Using trigonometry, eratosthenes was able to determine that the distance from syene to. Alexandria was about 5,000 stadia at an angle of 7 degrees. So the distance was 7/360 degrees of the entire circumference. He calculated the circumference of earth to be 250,000. Now a greek stadium was of a kilometer in length so his estimate of earth"s circumference was about 42,000 km. The modern value is around 40,100 km for an error of about 4. 74%. That"s actually really impressive given the time period! Based on this, eratosthenes concluded that the earth was not flat.
