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Eventually though, they'll both become locked to each other, with the same faces always pointing towards each other. That's if Sol doesn't nova before then.
Gravitational coupling between the Moon and the ocean bulge nearest the Moon affects its orbit. The Earth rotates on its axis in the very same direction, and roughly 27 times faster, than the Moon orbits the Earth. Thus, frictional coupling between the sea floors and ocean waters, as well as water's inertia, drags the peak of the near-Moon tidal bulge slightly forward of the imaginary line connecting the centers of the Earth and Moon. From the Moon's perspective, the center of mass of the near-Moon tidal bulge is perpetually slightly ahead of the point about which it is orbiting. Precisely the opposite effect occurs with the bulge farthest from the Moon; it lags behind the imaginary line. However it is 12,756 km farther away and has slightly less gravitational coupling to the Moon. Consequently, the Moon is constantly being gravitationally attracted forward in its orbit about the Earth. This gravitational coupling drains kinetic energy and angular momentum from the Earth's rotation (see also, Day and Leap second). In turn, angular momentum is added to the Moon's orbit, which lifts the Moon into a higher orbit with a longer period. The effect on the Moon's orbital radius is a small one, just 0.10 ppb/year, but results in a measurable 3.82 cm annual increase in the Earth-Moon distance. Cumulatively, this effect becomes ever more significant over time; since astronauts first landed on the Moon approximately 40 years ago, it is 1.51 metres farther away.
Vern it may be counterintuitive but jj73 is correct. You have to do the calculation in terms of the energy of the orbit. The orbit is higher an therefore possesses more potential energy the kinetic energy is reduced slightly but the total energy increases.Let me illustrate it like this say you are in a spacecraft in a circular orbit around a planet and you fire the motors briefly in the direction of travel and speed up the spacecraft. The orbit then becomes elliptical and you move further out to reach a maximum distance from the planet at the opposite position in the orbit from where you fired the motors as you do this you are slowing down all the time. If you do nothing you will return to the position where you fired the motors accelerating back to your final speed that was reached after firing the motors. Now if when you are furthest away from the planet and going at your slowest speed you fire the motors again in the direction of travel to speed up a little bit (but not to go as fast as you were in the original orbit) it is possible to restore a slower circular orbit at the higher altitude and all you have done is make the spacecraft go faster. The techniques of orbital energy changes are very unlike things on the earth's surface but work very accurately.You cannot go further out in a circular orbit by accelerating a spacecraft with a single impulse you need at least two the alternative is to do it extremely slowly with a continuous tiny acceleration force but the spacecraft actually slows down because more energy is going into raising the potential energy of the spacecraft than is increasing the kinetic energy.
I sent this to Chris but I think it is relevent in this topic; isn't it a series of big coincidences that the Earth, Moon and Sun are so perfectly proportioned and the distances are perfect in proportion to their sizes to creat such fabulous lunar and solar eclipeses? Does this happen routinely in the universe or are we "special" (lol)?