How Eratosthenes Estimated the Circumference of the Earth Over 2,000 Years Ago

Posted on August 25, 2016  Comments (4)

In this video Carl Sagan explains how Greek astronomer Eratosthenes, in 200 BC, was able to deduce and calculate the earth was a sphere about 40,000 km in circumference.

It is wonderful to see how a bit of thought and curiosity have lead mankind to learn so much.

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4 Responses to “How Eratosthenes Estimated the Circumference of the Earth Over 2,000 Years Ago”

  1. Conrad
    August 27th, 2016 @ 4:42 pm

    The YouTube video is saying an error occurred. However, it does seem like an interesting topic. I will check back later to see if it is working.

  2. curiouscat
    August 27th, 2016 @ 10:01 pm

    Ah, YouTube died when using the direct url with the start time. They seem to tell you to use a # instead of & that is found in the url when embedding on

    Doing that does allow the video to play. Though it doesn’t actually start it at the tie you give. YouTube, and Google more generally, are still providing absolutely horrible help files more than a decade after saying they aim to organize the world’s information. They still can’t even organize their own help system. That is pitiful.

  3. Conrad
    September 28th, 2016 @ 11:30 am

    I’m glad I was able to come back and watch the video. It is ever so interesting that someone thought to figure out the circumference based on the shadows of sticks. I really thought there was going to be more to the way it was determined. Thanks for sharing.

  4. Marbella
    October 16th, 2016 @ 3:46 pm

    This was really interesting. Thanks for sharing.

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