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Carl Sagan - Cosmos - Eratosthenes

carlsagandotcom · explainer · Watch on YouTube

World historyScientific method & science communicationPure mathematics

What it is

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 Hacker News recommends it

HN commenters link it whenever the question of how the Earth's size was first measured comes up, calling it a wonderful explanation.

  • 4 people recommended it
  • 4 different months
  • 1 strong recommendations
  • first 2022, last 2024

What HN commenters said

  1. “One of my favourite episodes of Cosmos centres around Eratosthenes’ calculation of the circumference of the Earth”

    Cosmos episode on Eratosthenes' calculation of Earth's circumference

    ubutler, 2024-03 · Strong recommendation · in “Webb and Hubble confirm Universe's expansion rate”

  2. “The video has a good explanation of how it was done.”

    Good explanation of how Eratosthenes estimated Earth's size

    hotpotamus, 2022-02 · Recommendation · in “Zen and the Art of Talking to Conspiracy Theorists”

  3. “Carl Sagan's explanation on Cosmos of Eratosthenes' discovery is great”

    Sagan's explanation of Eratosthenes' discovery

    jamesgill, 2023-01 · Recommendation · in “Interesting”

  4. “Here is a wonderful video of Carl Sagan explaining it[0].”

    Sagan explaining how Earth's size was measured

    kemotep, 2023-08 · Recommendation · in “How was the size of Earth first measured?”

Excerpts from Hacker News comments, linked to the originals. Summaries and labels were written by a language model from those comments.

Topics: eratosthenes, carl sagan, cosmos, astronomy history, geometry

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