Who is erasthostenis?

Answer 1

Eratosthenes was an ancient Greek philosopher who devised a way to measure the size of the earth. He noted the time when the sun shone straight down a deep well in Egypt, and how long it took before the sun was directly overhead at another location, and then had a runner estimate the distance between the two locations. He knew what fraction of a day the difference in time represented, and he knew that the measured distance was the same fraction of the earth's circumference. I don't know what number he came up with, but considering the methods he used, he was surprisingly close to the accurate answer. Notice that although he was working a couple of thousand years ago, he was assuming a spherical earth, not a flat earth.