Eratosthenes calculated the circumference of Earth by measuring the angle of the shadow cast by the Sun at noon in two different locations and using this information to determine the distance between the two points on Earth’s surface. He first measured the angle of the shadow cast in Alexandria, Egypt, which he found to be around 7.2 degrees. At the same time, he also measured the angle of the shadow cast in Syene (now Aswan), which was found to be virtually nonexistent as the Sun was directly o