Eratosthenes
June 19, 240 BC - Today was the day that a Greek mathematician and all-around genius named Eratosthenes estimated the circumference of the Earth - and despite the limited resources he had at the time, his estimate was remarkably accurate - within 2% of the actual measurement.
Eratosthenes was the head librarian at the Great Library of Alexandria. He’s remembered as the father of geography, and the first to lay down a grid of meridians and parallels.
If you have a couple minutes to burn, check out the video below for a quick explanation about how Eratosthenes measured the Earth:
