Re: An ancient Greek (Archimedes ?) measured Earth's diameter.How did he do it?

Hi there,

I think the bloke that you're after was Erathostenes of Cyrene, who used the shadow of the Sun at noon in two different places to measure the size of the Earth. He reasoned that if the Earth was curved, the Sun would cast shadows at different angles in different places. Measurement of those angles, along with the distance between the points where the measurements are made, can then give you the size of the Earth. To read up on exactly how it works, take a look at the European Southern Observatory's Erathostenes web page.

Jim O'Donnell