How did Eratosthenes figure out Earth is round and calculated earth circumference 2000 years ago?
In: Mathematics
Erastosthenes measured the shadow cast by two Obelisks on the same day, both at high noon. One was in Alexandria, and (with help from an assistant) the other was in Southern Egypt. If the Earth was flat, the shadows would be the same length, due to having the same angle relative to the sun. Instead, the lengths were different, and because the distance between the two cities were known, Erastosthenes could use geometry to estimate the difference in angles between the two obelisks, relative to each other. From there, he could use geometry to calculate the distance necessary to achieve 360 degrees, a circle.
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