Calculate the circumference of the Earth using this equation: Circumference = 360 x distance between your city and the equator / angle of shadow that you measured What value do you get?

The circumference of a circle is its outside edge, and is the same distance from the centre at every point along its length. This distance is called the radius.

When you look out of the window of a plane, everything looks so small. But they're all big enough to do some awesome physics.