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    Carl Sagan - Cosmos - Eratosthenes

    carlsagandotcom

    4 HN recommenders · recommended in 4 months, 2022–2024

    YouTube

    6:42 · 3M views · Apr 24, 2009

    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

    1. @ubutlerMar 2024· in “Webb and Hubble confirm Universe's expansion rate”

      One of my favourite episodes of Cosmos centres around Eratosthenes’ calculation of the circumference of the Earth: this video

      Strongly recommendsView on HN
    2. @hotpotamusFeb 2022· in “Zen and the Art of Talking to Conspiracy Theorists”

      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 )

      RecommendsView on HN
    3. @kemotepAug 2023· in “How was the size of Earth first measured?”

      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

      RecommendsView on HN
    4. @jamesgillJan 2023· in “Interesting”

      Likely familiar to this crowd, but Carl Sagan's explanation on Cosmos of Eratosthenes' discovery is great: this video

      RecommendsView on HN