How did Eratosthenes calculate the circumference of the Earth?
Eratosthenes was a smart person who lived a long time ago. He figured out how big the Earth was by using the sun and a stick. He saw that in one place, the sun was straight above a deep hole, but in another place, the sun was at an angle and made a shadow. He measured the angle of the shadow and used math to find out how big the Earth was. He found that it was around 39,375 kilometres, which is close to what we know today.