On March 20th, Spring Equinox and International Earth Day, in the framework of Erasmus+ΚΑ2 ‘’Climate Change Ready/CCR’’, B class students and their Geometry teacher, Mr P. Chronopoulos, conducted Eratosthenes’ experiment in Ralleio school courtyard. The Geometry lesson started with a classroom theoretical discussion about Eratosthenes of Cyrene (c. 276 BC– c. 195/194 BC), a Greek mathematician, geographer, poet, astronomer and music theorist who was the chief librarian at the Library of Alexandria and invented the discipline of geography, including the terminology used today. He is best known for being the first person to calculate the circumference of the Earth, which he did by comparing angles of the mid-day Sun at two places a known North-South distance apart. He was also the first to calculate the tilt of the Earth's axis, again with remarkable accuracy.

At Ralleio courtyard, the students measured the shadow of a long metal ruler, placed vertically on the floor at 12.35 pm, and calculated the tangent of the angle formed by the shadow of the object and its height. Based on Ralleio geographical latitude and its distance from the equator at the same meridian, they calculated the Earth’s radius with less than 0,18 % deviation. The whole activity was based on a Worksheet designed by Serres Educational Centre for Natural sciences.

After the activity, the group discussed their experience, which was a classroom lesson follow-up activity, and realized that Technology is not always necessary for “leaps of thought”. The objectives of this activity were for the students to understand the way in which Eratosthenes worked in the 3rd century BC and to use their Geometry knowledge outside the classroom working in groups. The aim of this activity was the better understanding of the approximately spherical shape of the Earth.