Circles and PiEarth Arc

Most scientists in ancient Greece agreed that the Earth is a sphere. There was plenty of evidence: from ships disappearing behind the horizon at sea, to the circular motion of stars during the night.

Unfortunately, no one knew exactly how big Earth was – until around 200 BC, when the mathematician Eratosthenes found an ingenious way to measure Earth’s radius, using basic geometry. All we need is a bit more knowledge about arcs and sectors of a circle.