Eratosthenes... knew that the Sun was straight overhead in... Syene at noon on the summer solstice, but that it was 7.2 degrees south of straight overhead in , located 794 kilometers farther north. He concluded... 794 kilometers corresponded to 7.2 degrees out of the 360 degrees... around Earth's circumference, so that the circumference must be... 39,700 km...

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Source: Wikiquote: Max Tegmark, CC BY-SA 4.0