Eratosthenes’ Experiment

Under the scheme of the SLAM Erasmus+ Project, we repeated an experiment firstly conducted by Eratosthenes around 2000 years ago. The aim of the experiment was to estimate the circumference of earth based on simple concepts from physics and geometry.

We set up a 1 meter stick vertically on the ground and measured its shadow at exactly 12:40 (the solar noon) on the 23rd of September. The students then measured the length of the stick’s shadow as shown above.

Then they used trigonometry to find the angle the light rays made with the stick which was 34.8 degrees.

By the alternate interior angles theorem, this angle is also the angular distance of our school from the Equator. This is explained by the fact that sun rays at that time of the year are perpendicular to the Equator.

Using Google maps, we calculated the distance between our school to the Equator and finally using our angular distance from the Equator, we found the circumference of earth equal to 40 035 km which is quite close to the actual average value of 40 075 km.