In 240 B.C., the Greek astronomer Eratosthenes made the first good measurement of the size of Earth. By noting the angles of shadows in two cities on the Summer Solstice, and by performing the right calculations using his knowledge of geometry and the distance between the cities, Eratosthenes was able to make a remarkably accurate calculation of the circumference of Earth.

To re-live this historical moment, GTTP invited the friends around the world to send in measurements taken at the true solar noon on 21 June 2013. And they responded! GTTP friends from Romania, Tanzania, Serbia, Argentina, Ireland, Ghana and more sent in measurements.

Enjoy the more photos of Eratosthenes measurements taking around world on GTTP Facebook.