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Carl Sagan - Cosmos - Eratosthenes
carlsagandotcom
A short clip from Carl Sagan's Cosmos in which he explains how Eratosthenes measured the circumference of the Earth using shadows in two Egyptian cities. It is a clear, visual account of an ancient scientific feat.
HN commenters link it whenever the question of how the Earth's size was first measured comes up, calling it a wonderful explanation.
4 Hacker News mentions · 2022–2024