The moons I have seen faces the planet with the same side?

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The moons I have seen faces the planet with the same side?

Post #1by Evileye » 19.08.2002, 19:17

I have visited all faced the planet whith there same side.
Is that a defaul option or is that correct rotational revolution of the moons?
I wonder why this is....?


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Post #2by chris » 19.08.2002, 20:25

This is correct for almost all moons in the solar system . . . Tidal forces cause the rotations of moons to slow down until they match the orbital periods and the same side of the moon always faces the planet. This is why we only every see one side of our moon from the Earth. The same tidal forces also cause the planet's rotation to slow . . . Eventually, the rotation of the Earth will slow down to the point where it matches the orbital period of the Moon--days will be a month long, and the Moon will only ever be visible from one hemisphere. Such mutual tidal locking has already occurred in the Pluto-Charon system--start up Celestia and visit it!

Most moons have slightly inclined or eccentric orbits which cause their parent planets to wobble slightly in the sky. A few such as Saturn's moon Phoebe are distant enough that they've so far escaped tidal locking. Mercury is almost in synchronous rotation, but it's orbital eccentricity is such that it's in a 3:2 resonance--it rotates about it's axis three times every two orbits around the sun. That is, Mercury's year is equal to 1.5 of its days!


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