NASA Logo, National Aeronautics and Space Administration
Ancient Observatories Timeless Knowledge

Sun-Earth Day Presents: Ancient Observatories, Timeless Knowledge


Using the eratosthenes method, calculate the circumference of the Earth

This is a tad off topic but symbolizes the use of pre telescopic observations of the sun to understand our world. Over two thousand years ago, the knowledge existed that the Earth was round. Observing the changing height of the North Star or watching ship masts disappear over the horizon after the ship had disappeared provided evidence of a round Earth. But how big? That was a little more difficult. The Greek librarian and astronomer, Eratosthenes (275-194 BC) developed a method for deriving the circumference of the Earth by noticing that the noon time sun cast different length shadows in different locations on the Earth. You can replicate this historic finding by measuring the length of the shadow cast by a gnomon for two different latitudes. For complete instructions on how this is done, go to The Eratosthenes Project.


Recommended Links

NASA Logo -