Even as the Moon changes phases throughout the month, we are always seeing the same face (the half facing us) of the moon! If you don't believe me, take a long look at this photo series (above) of the Moon over one month. This picture was copied from: http://startswithabang.com/.
How does that work? The moon rotates on its axis, just like Earth's rotates, so why aren't we seeing the whole sphere??
The Answer: The moon rotates once in 29.5 days and also orbits Earth once every 29.5 days. Because the rates of rotation and revolution are the same, the moon does APPEAR to rotate to an observer on Earth. Outside observers, however, would be able to see the moon rotating when observing the Sun, Moon, Earth system.
Here's one explanation: http://www.badastronomy.com/bad/misc/moon_spin.html
And here's another: http://startswithabang.com/?p=398
Here's a fun way to remember this:
Oh, glorious Moon!
As I gaze on your face
it comes to my mind
That never shall I gaze
On your glorious behind.
--Anonymous
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