This still gives me chills. Ingenious. Carl Sagan explains how the Ancient Greeks, Eratosthenes of Cyrene, the chief librarian at the Library of Alexandria, inferred that the Earth was round and calculated its circumference 2200 years ago. 240BC
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Replying to @noornet @SwiftOnSecurity
Brilliant. I’m interested to understand how they knew the length of the shadows “at the same time”, can someone explain?

Sep 30, 2019 · 5:40 AM UTC
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