Deriving Earth's circumference, the ancient way

Skylar Larsen | EAPS News
Friday, May 15, 2020

My name is Skylar, and I am an American Association of Variable Star Observers (AAVSO) ambassador. Currently I am an undergraduate freshman at MIT, taking the class 12.409 (Observational Astronomy) under EAPS Professor Amanda Bosh. This spring, the class became an "online lab". Bosh and Wallace Observatory Director Mike Person creatively rearranged the course to take advantage of the fact that many students in 12.409 were scattered around the globe, and are now studying at home, to re-create an ancient experiment that measures the circumference of the Earth. To do this, Person asked them to make simultaneous measurements of the length of a shadow just after class one day. He then combined these measurements to re-derive the circumference of the Earth, thereby recreating a famous historical experiment done by Eratosthenes in approx. 240 BC.

Join me as I explain the history, math, and science behind it.