Eratosthenes and the Measurement of the Earth's Circumference (c.230BC)

In the third century BC, Eratosthenes (then Chief Librarian of the Great Library of Alexandria) attempted to calculate the circumference of the Earth based upon the shadows cast by the pointers of sundials located in Alexandria and Syene at midday on the Summer Solstice, and based upon several other pieces of assumed knowledge from the time. The results of this experiment and calculation were given in a unit of measure called the stade. Debate over the accuracy of Eratosthenes’ calculation has been ongoing since he first conducted the experiment ca. 230 BC—in part by the difficulties in converting the size of Eratosthenes’ stade into a modern equivalent. This work engages with this long-running debate (one of the longest ongoing debates in the history of science) by applying innovative and multi-disciplinary methods such as linguistic analysis, mathematical modelling, satellite mapping, archaeological investigation, and historical examination to create the first ever combined exploration of this important event in the history of astronomy. The results of this examination demonstrate that that Eratosthenes was one of the first precise observers of celestial phenomena, and that he was able to calculate the size of our world to a very high level of accuracy.

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