Eratosthenes

- I learned something interesting in school yesterday. Apparently, around the 2nd century BC, a guy named Eratosthenes was studying in the library at Alexandria, when he came across an account that stated that on a paticular day each year (the professor couldn't remember what day it was), the sun shines into a well at Syene and casts no shadows (shines directly inside it, illuminating the whole thing). Erat went out on that specific day, and checked all the wells around him, and none of them did the same. So he paid a guy to pace off the distance between Alexandria and Syene (which is quite a ways, if you'd like to check in out on a map). When the guy returned, Erat used the information, the sun angle on his own well, and what the angle would have to be on the other well, and he then estimated the curvature of the earth. Since they all knew that the earth was 360 degrees, but simply had no way to measure each degree, and Erat had learned the distance of degrees between Alexandria and Syene, he correctly estimated the size of the Earth to within 20 kilometers. Sometime around the 2nd century BC.

I thought that was awesome, but I'm a nerd.