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I haven't ever tried to calculate what will happen when the earth-moon system tidally locks with the sun. Safe to say it's not going to happen for a long, long time, but let me think about it...
My instinct is that over the long haul, the tiny tidal bulge will work towards locking the earth with the sun, which will cause the earth to move away (Neptune is demonstrably moving away from the sun, which is why Pluto and other KBOs are trapped in resonance orbits with Neptune) and slow down, which will in turn cause the moon to slow down and move away from the earth to keep up. Unless the moon is orbiting in the opposite sense, which I don't remember off the top of my head. Anyway, I suspect that eventually the moon will get stripped off the earth into its own solar orbit, but I haven't tried to caluclate that for sure.
I have to go to a meeting,
Don
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I found this from Phil's page on tides. Warning, lots o' math, but it's good.
http://www.jal.cc.il.us/~mikolajsawicki/tides_new2.pdf
Here's a bit on what it has on my question:
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...the Moon speeds up in its orbit and moves away from the Earth, at the rate of some 4 meters per 100 years, and the orbital period of the Moon increases too. However, since the orbital period of the Moon increases at smaller rate than the length of the day does, both periods will eventually match. The Earth will be then tidally locked with the Moon, and the length of the day and the month will both be equal to some 50 present days, with the same side of Earth always facing the Moon. Note that the same side of the Moon already always faces the Earth, as the tidal action of the Earth on the Moon caused the Moon’s original spin to slow down, and Moon became tidally locked with the Earth long time ago, in the sense that the Moon spins once on its axis for each revolution around the Earth.
Once the Earth becomes tidally locked with the Moon, the solar tides will tend to slow the Earth’s rotation even more, so that the day will be longer than the month and the Moon will rise in the West and set in the East. The water spheroid generated by the Sun will cause the high tide to appear earlier than the time of highest moon, a situation exactly opposite to that of Fig. 2. Then the tidal force of Earth on the Moon will slow the Moon down in its orbit, forcing the Moon into a lower orbit until and eventually inside the Roche limit (18500 km), whereupon the Moon will disintegrate producing a ring around the Earth.
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Wheee! We get a ring!! OK, we'll all be dead by then, but it's the principle of the thing.
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Jeff Schwarz
<font size=-1>[ This Message was edited by: Geo3gh on 2002-03-18 15:44 ]</font>