In which location did Eratosthenes observe that the sun shone directly down a deep well at noon on the summer solstice?

Answer

Syene (modern Aswan, Egypt)

In Syene, the sun was precisely overhead at that specific time, meaning no shadow was cast by vertical objects, which provided a zero-degree reference point.

In which location did Eratosthenes observe that the sun shone directly down a deep well at noon on the summer solstice?

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