The Egyptian City Where the Sun Stood Directly Overhead at Noon on the Summer Solstice
Syene — modern Aswan, at the First Cataract of the Nile — sits almost exactly on the Tropic of Cancer. At noon on the summer solstice the Sun stood directly overhead and cast no shadow. That geographical fact gave Eratosthenes the second measurement he needed to compute the size of the Earth in the 3rd century BC.
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