Eratosthenes' Calculation of the Earth's Circumference s



by Lookang
published on 05 April 2013

An illustration showing Greek scientist Eratosthenes' method for calculating the circumference of the Earth. By measuring the angle of a shadow in one location (Alexandria) and comparing at the same time with a second point (Syene) where the sun was directly overhead and created no shadow and by calculating the distance between these two points, Eratosthenes was able to calculate the curvature of the earth between the two points and extrapolate that figure to calculate the circumference of the earth. He arrived at a figure only 15% inaccurate and that probably due to the unreliable distance figure between the two points rather than any error in his mathematics.

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