Question

How did Eratosthenes determine the circumference of the Earth?

Answer 1

Eratosthenes calculated the Earth's circumference without leaving Alexandria. He knew that at local noon on the summer solstice in Syene (modern Aswan, Egypt), the Sun was directly overhead. ... Using the length of the rod, and the length of the shadow, as the legs of a triangle, he calculated the angle of the Sun's rays.

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