As Eratosthenes 2200 years ago, we will measure the Earth's circunference at summer's solstice (H.N, i.e. 21 June). All schools can participate: they will have to send us their measurement.

The method consists of putting a staff on the floor exposed to the sun, measure its shadow when the sun is at its highest point, deduce the angle of the solar rays compared with the vertical staff, then exchange your results with another class under another latitude. Then, a few geometrical drawings and a rule of three give you the length of earth's radius.

The video you can download at the following link (wmv, 14Mb, 2 min, credit: Planetario de Milano) gives you a good idea of the project's science.

In 2009, the project was also developed between schools of Barcelona (Spain), of the Republic of Bénin and of France.

June 21, 2015 measurement:

September 21, 2015 measurement:

How did Eratosthenes calculate the size of the Earth?

Here you can find the necessary documents to the Eratosthenes experiment.

There are materials that may be of interest to complement the main subject of "Eratosthenes project".

For the Eratosthenes experiment at school students can measure the angle at the top using a protractor as shown in the image bellow.

How to convert latitude in different systems?

Eratosthenes used a simple formula that relates the proportionality of the relation of the distance between two places on the meridian (d) and their difference in latitude (α) to the relation between the perimeter (P) and the angle of the hole meridian (360º)

Some questions, and answers, about this projects.

Results of the measurements that were made by schools in September 2014.

The organization of Eratosthenes in the International Year of Light has released the results of the measurements that were made by schools between the 14th and 25th of September 2015.

There are partners of the Eratosthenes project.