Re: If the moon is moving away, Is it also comming closer?

Rob,

You're quite right, the moon is moving away from the Earth at a rate of about 4 cm per year, however it's due to the action of tides here on Earth. The tides are caused by the effects of the Moon's gravity on the oceans and the Earth. The short explanation uses Newton's law of universal gravitation ( Two bodies attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. ). This tells us that the water in the oceans closest to the Moon has a greater force on it from the Moon, than the force on the Earth or on the water on the opposite side of the Earth. You get bulges of water on either side of the Earth which are the tides.

The Earth rotates about its axis much more rapidly than the Moon travels arround the Earth. Since the Earth is rotating faster it carries the bulges ahead with it so that the tide is always a little ahead of the Moon. Newton's law said that two bodies attract each other so the bulge is constantly pulling the Moon ahead in its orbit. The effect, the bulge is lifting the Moon into a higher orbit.

This will continue to happen as long as the Earth's rotation is greater that the Moon's revolution arround the Earth. The friction between the oceans and the Earth's surface is constantly slowing the rotation down by about .002 seconds per century. What that means is that many Moons from now, when the length of a day equals about 47 of our current days, the bulges will align directly below the Moon and the separation will cease.

Hope this helps.

Mike Francis
http://www.gis.net/~mtf/sm.htm