We always see the same face of the moon, because
(A) it is smaller than the earth
(B) it revolves on its axis in a direction opposite to that of the earth
(C) it takes equal time for revolution around the earth and rotation on its own axis
(D) it rotates at the same speed as the earth around the sun
Correct Answer : it takes equal time for revolution around the earth and rotation on its own axis
Question Asked : SSC Tax Assistant (Income Tax & Central Excise) Exam 2007
Explanation : It is tidal locking that causes the synchronous rotation of the Moon to present "just one side" to the Earth all the time. The Moon rotates (spins) but very slowly, making one turn on its axis in the same time it takes to revolve (orbit) around the Earth. So it maintains a "constant face" in our direction. We actually see slightly more than half of its surface as it turns. Tidal locking (or captured rotation) occurs when the gravitational gradient makes one side of an astronomical body always face another, an effect known as synchronous rotation.
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