Measuring the radius of the Earth. An educative experience

On the occasion of the 4th centenary of Galileo's first use of the telescope for astronomical purposes, an astronomical association in Barcelona proposed to teaching centers, the project of measuring the radius of the Earth, using ancient Eratostenes method. More than 600 centers took part on the project. Each center had to take data about the positioning and the length of the shadow casted by vertical stick on March 26th. Once the data was taken and sent to the coordination center, the mean distance to the center of the Earth can be measured. Although the results were not precise, they were satisfactory enough. It was also a very interesting educational experience on scientific investigation.