On 2002-03-18 10:28, Gary Redmond wrote:
Glad to meet all of you. This being my first post (perhaps last) please forgive any faux pas.
This is to address the first post by Geo3gh.
"These are the things that keep me up at night."
Perhaps you are asking the wrong questions. Sorry!
BTW I never sleep well.
"The Moon is gradually moving away from the Earth at a rate of a few cm a year."
The Earth-Moon system moving apart by 3-4 cm per year is experimental fact.
However the following is (astronomy book) conjecture:
"This has the additional effect of causing the Earth to rotate on its axis more slowly. Eventually the Earth will find itself tidally locked with the Moon. Both bodies will show only one face to each other."
The facts are:
The Moon does run slow (recession of nodes), however there is no evidence that it is "slowing".
The Earth does run slow (leap second), again there is no evidence that it is "slowing".
I'm not completely sure on this, but I don't believe that the gravitational mass can effect the rotation of the inertial mass.
If you locate the center of gravity of a mass (point around which all its weight is equally distributed) and then suspend that mass from that point it will be in perfect balance and will not rotate, or will continue to rotate indefinitely. The Earth's center of gravity suspends the Moon's center of gravity and vice versa. Thus the Earth cannot rotate the Moon, and the Moon cannot rotate the Earth. Furthermore, tides are internal to a system so therefore they cannot change the angular momentum of the system.
"3) Since there is also a tide from the Sun (although smaller than the tide from the Moon) I presume that the Earth will become tidally locked to the Sun. How long will this take?"
If the Earth were locked to the Sun, the Moon were locked to the Earth, and the Earth were locked to the Moon, the Earth Moon system would no-longer rotate the Moon would crash straight down and the Earth and Moon would become one mass:-)