Today, a short but earth-shaking bit of science, from over 2000 years ago.
The story of Eratosthenes and Earth’s circumference, as told by Carl Sagan
After hearing that the shadows disappeared at noon in the town of Syene (now known as Aswan), Eratosthenes achieved his understanding of our planet’s size by comparing the angle of the sun’s rays in the port city of Alexandria-at the same time.
The Sagan video won’t post for whatever reason, but this is the link:
Carl Sagan – Cosmos – Eratosthenes
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J.R. Johnson 
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