Wednesday, January 14, 2009

The moon isn't turning around the Earth

Surprising right, but it actually true, the moon does not rotate around the Earth, its rotating around the sun and making a sinusoidale patern around the Earth. Now this illustrate a little misconception a lot of people have about gravity. You see the force of gravity doesn’t point exactly to the center of the most massive object. It points to the center of mass of the system, that means that for exemple the Earth-Moon system (if it existed outside everything else in the universe) would orbit not around the center of the Earth but around a point that correspond to center of the mass distribution between the Earth and the moon. Now since that Earth is much more massive then the moon this point is currently inside that Earth’s crust, but if the moon was farther away it could move outside the Earth and both would be turning around empty space. Fascinating isnt it? Oh and btw that also means that you are attracting the Earth toward you with the same force as the Earth is attracting you toward it.

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