He Measured Earth With Two Shadows

Added: 2026-05-27

[00:00:00]How do you measure a planet using only a well? In 240 BC, the librarian Eratosthenes heard that in Syene, the [music] solstice sun cast no shadow down a deep well. But in his city, Alexandria, [music] an obelisk cast a clear shadow. He measured the angle, 7.2 degrees, >> [music] >> or exactly 1/50 of a circle. Knowing the distance between the cities was 5,000 stadia, he multiplied by 50. The result, he calculated Earth's circumference and missed by less than 2%. Like and subscribe for more Time Prime History.