Measuring the Earth's Circumference

Published on 22 September 2016 by Mrs Fiona MacFarlane Categories: Senior School

S2 Physics pupils undertaking the experiment in the quadSome pupils in S2 were able to measure the circumference of the Earth today to 99.5% accuracy, using only meter sticks and the sun.

This experiment follows in the footsteps of Eratosthenes who measured the circumference of the Earth more than 2,000 years ago. He noticed that a shadow was created in Alexandria in Egypt at noon on the Summer Solstice but no shadow was formed at Syene. By using simple geometry, he was able to determine the circumference of the Earth to a high degree of accuracy.

Today, at the solar noon (1.05pm), the length of a shadow of a metre stick was 145cm in the West Quad. This data was shared with over 400 other schools doing the same experiment around the world. Using the same geometry that Eratosthenes used, the circumference of the Earth was determined to be 40,280 km, a surprisingly accurate result. Only more surprising was the fact that the sun was shining sufficiently for the pupils to conduct the experiment in the first place!

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