Why Do We only See One Side of the Moon?
Alexandra: (Alex looking up to the moon with a telescope). This one's for all you romantics out there. When you stare up at the moon, do you ever notice you always see the same side of moon facing the Earth?
A lot of people think it's because the moon does not rotate. Surprise! The moon does rotate.
So how come we always see the same side?
First, let's start the moon rotating on its axis (animation of the moon rotating). You would think that we would see all the sides. But now, let's put the moon in orbit around the Earth (animation of moon rotating while orbiting the Earth with vector showing same side facing Earth). The time in which the moon rotates once is the same amount of time it takes to orbit around the Earth once.
The moon's rotation and revolution speeds are synchronized so the moon is in a type of synchronous orbit. The result – from Earth's point of view we always see the same side of our rotating moon.
By the way, if you were on the near side of the moon, you would see our rotating Earth fixed in the same spot in the sky…all the time (picture of rising Earth from moon). Think about it!
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NASA Brain Bite BB1801B