Wednesday, March 03, 2010

Dark side of the moon

No, this post is not about the awesome Pink Floyd album. It's about the real dark side of the moon. As some of you well know, the moon has a dark side or a "far" side, which constantly faces away from the earth. And a "near" side which constantly faces the earth. In other words, it takes the Moon exactly the same amount of time to rotate around its axis as it does for it to go around the Earth once (~27.322 days). Ever wondered why this happens?

This phenomenon is known as synchronous rotation and it is quite common between planets and their satellites. It is caused due to something known as tidal locking. Just like the moon affects the tides on the earth, the mass and speed of rotation of the earth influences the moon, but in a much larger way (because the earth is much more massive). Early in its life, the moon spun much faster. But slowly, its rotation locked in with its revolution around the earth due to the tidal forces, and we got the "near side" and the "far side". The Wikipedia link above has more info if you are interested in further reading.

Turns out almost all moons in the solar system are tidally locked with their corresponding planets. In fact, Pluto and its moon Charon, are tidally locked with each other i.e. both of them show just one side to other and revolve around each other as if joined with a rod. Astonishing!!!