Open Discovery Space

“Eratosthenes’ measurement of the Earth’s Circumference” is an activity that engages ODS schools in international cooperation. Students from schools across the world measure the Earth’s circumference by performing the experiment of Eratosthenes, originally carried out in the 3rd century B.C.

Over 120 schools have already registered to participate to this year’s event! At their respective noontimes on the equinox day – 21st of March – the students will measure the length of shadows cast by sticks, then consult the observations made by others at the same latitude. By sharing this data, invoking the properties of right triangles and applying proportional reasoning to angular distances, the students will obtain a good measurement of our planet’s size.

What do you need to do?

  • Register by completing the name, longitude and latitude of your school.
  • Find a registered school at the same longitude with you.
  • Join efforts with the matching school and record your data.
  • Calculate the circumference of the Earth.

This year the experiment will take place on the 21st of March, on the equinox day. Thus, for your matchup –if no other schools can be found on the same longitude – you can consider the existence of a virtual school on the equator with experimental data 0 (shade of a one-meter stick measured at a certain time). This way you can also have an accurate outcome by conducting the experiment by yourself.

Join today and let your school be part of an exciting international activity! For more information, please visit the website:

The Eratosthenes Experiment is organized in the framework of the European Commission’s Open Discovery Space project.


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