In the Footsteps of Eratosthenes


In the Footsteps of Eratosthenes


Resource type

Classroom resource

The collaborative project In the Footsteps of Eratosthenes, implemented by the Fondation La main à la pâte, began in September 2000 and has already led thousands of pupils aged from 8 to 14 to measure the Earth's circumference from their classrooms, simply by observing the shadow of a vertical stick (gnomon) at solar noon. Each year, schools in many countries join forces to replicate the observations of the Greek scientist Eratosthenes who, more than 2,200 years ago, was the first to propose a simple and original method to measure the size of our planet.

The project is made up of five activities, but its implementation can be adapted according to a number of contingencies: the age, level and motivation of the pupils, the size of the group, the time available to devote to this project, not forgetting the vagaries of the weather... 

Thus, shortcuts are possible, but the "minimum course" is marked out by five stages: 

  1. Jointly highlight the curvature of the earth's surface and the parallelism of the sun's rays.
  2. Observe the evolution of the shadow of a stick and deduce the trajectory of the Sun.
  3. To discover the moment of solar noon (the moment when the shadow is the shortest).
  4. To use a gnomon to deduce the angle of the sun's rays with the vertical.
  5. Use a pen pal's reading and locate the two partner classes on a map to estimate the length of the earth's meridian.

The five activity sequences of the project :

  • Discover the observations of Eratosthenes and try to reproduce them 
  • Make and use gnomons
  • Discover the solar noon
  • Measure the angle between the sun's rays and the vertical
  • Measure the size of the Earth


> Learn more about this project