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Carl Sagan - Cosmos - Eratosthenes
About this video
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.
Why it appears in the archive
HN commenters link it whenever the question of how the Earth's size was first measured comes up, calling it a wonderful explanation.
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From the Hacker News discussion
One of my favourite episodes of Cosmos centres around Eratosthenes’ calculation of the circumference of the Earth: [VIDEO]
Read original comment ↗Carl Sagan talked about Eratosthenes in Cosmos[0] actually which is what I was thinking of. He was also able to make a good estimate of the size of the Earth as well. The video has a good explanation of how it was done. [0]( [VIDEO] )
Read original comment ↗Likely familiar to this crowd, but Carl Sagan's explanation on Cosmos of Eratosthenes' discovery is great: [VIDEO]
Read original comment ↗I heard it was using a military unit’s standard marching pace to calculate the distance. Here is a wonderful video of Carl Sagan explaining it[0]. [0]: [VIDEO]
Read original comment ↗