Eratosthenes Experience

With the launch of the Era of space exploration in the middle of the last century, We were able to launch many satellites, We were able to accurately measure the circumference of the earth, And we reached the number 40.030 km.

Imagine that 2200 years ago, a very intelligent man managed to arrive at a value amazingly close to the true value of the Earth’s circumference, all with just a stick.

This man was Eratosthenes, a Greek scientist, who headed the library of Alexandria in his time.

He had knowledge from previous readings that on June 22, Which the “summer equinox” every year at exactly twelve after noon, Columns and buildings in Aswan, Southern Egypt, don’t have shades because the sun’s rays are perpendicular to the surface of the Earth.

He decided to test, as the same thing was happening in Alexandria, so he planted a stick vertically and waited until June 22, at exactly twelve after noon, in order to see whether the sticks had a shadow or not.

Eratosthenes noticed the presence of a shadow at an angle of about 7.2 degrees, he directly concluded that if the sun’s rays reach the earth at the same angle and at the same time, and the sticks in Alexandria have a shadow and in Aswan they have no shadow, then the surface of the earth must be curved and therefore the earth is spherical.

So Eratosthenes used his observation to calculate the circumference of the globe since the difference is shade between Alexandria and Aswan is 7,2 degrees, which means that the difference between the two cities is 7,2 degrees out of the 360 degrees that represent the entire surface of the earth.

Eratosthenes hire a man to measure the distance between Alexandria and Aswan and found that it was equivalent to 800 km.

By using a very simple equation, he was able to calculate the circumference of the earth to find 40.000 :


It is as simple as that, 2200 years ago, a man was able to calculate the circumference of the earth with amazing accuracy with a stick and clever work.

Unfortunately, in our time there are many sticks, yet many are afraid of reaching this simple result.

Beğen  9
Rajae Ouherra

Student- Department of Physics. Mars on Earth Project (MoEP) Author and MoEP-Morocco Chapter Coordinator

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