Carl Sagan - Cosmos - Eratosthenes
carlsagandotcom4 HN recommenders · recommended in 4 months, 2022-2024
3M views · 17 years ago · explainer · evergreen
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.
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4 comments from Hacker News
One of my favourite episodes of Cosmos centres around Eratosthenes’ calculation of the circumference of the Earth: ▶ this video
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]: ▶ this video
Likely familiar to this crowd, but Carl Sagan's explanation on Cosmos of Eratosthenes' discovery is great: ▶ this video
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]( ▶ this video )