Sagan explains how the ancient Greeks knew the Earth was round and calculated it's circumference over 2,000 years ago
@yogthos Knowing the earth was a globe, and it's size, and that shadows were different lengths at different times of year Eratosthenes also calculated the Earth's axial tilt!
However, his original writings have been lost; what Sagan describes is a *simplified* version of Eratosthenes calculations passed down to us by the scholar Cleomedes. Eratosthenes somehow also accounted for Syene not being exactly on the Tropic of Cancer, or directly south of Alexandria.
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