Definition: The earth is shaped not as a sphere but as an oblate ellipsoid or geoid (which simply means "earth shaped.") The earth is widest at the equator due to gravity and rotation. The earth is 24,901.55 miles around at the equator and 24,859.82 miles between the North and South Poles. The difference between the two is 41.73 miles.
Shape of the Earth
By Matt Rosenberg, About.com Guide
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