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header image Measure the Earth with Shadows  
 

More than 2000 years ago, the Greek scientist Eratosthenes first measured the circumference of the Earth with an ingenious technique requiring only sticks, shadows and a little mathematics. This past Spring, over 700 schools from all over North America participated in recreating this momentous experiment in celebration of the World Year of Physics 2005. Thank you to all our participants who made this such a successful project. The Grand Average, calculated from all the submitted answers, appears below.

Find out more about Eratosthenes and his experiment.

Download the Teacher's Guide (pdf)

See pictures from a participating school

Project Results

Grand Average of the Earth's Radius

6562.568 km (4078.663 Miles)
This value only contains a 3% error from the true value of 6371.3 km (3959 Miles)!

Locations of Participating Schools*

  
 

*Note: Due to mapping software's limited ability, not all schools in Mexico, Canada, and Puerto Rico are shown.

  
World Year of Physics 2005