Explain why the earth is not a perfectly round sphere.

As countless photos from space can attest, Earth is round—the "Blue Marble," as astronauts have affectionately dubbed it. Appearances, however, can be deceiving. Planet Earth is not, in fact, perfectly round.

This is not to say Earth is flat. Well before Columbus sailed the ocean blue, Aristotle and other ancient Greek scholars proposed that Earth was round. This was based on a number of observations, such as the fact that departing ships not only appeared smaller as they sailed away but also seemed to sink into the horizon, as one might expect if sailing across a ball says geographer Bill Carstensen of Virginia Tech in Blacksburg.

Earth is actually an oblate spheroid. This is a fancy word that means it is a slightly flattened sphere. Sort of like a skittle candy, except not quite as flattened. This is due to Earth spinning on its axis. The spin of Earth causes it to bulge slightly at the equator.

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