ANSWERS: 3
  • Hm. I think you are attempting to describe 'tide lock'. The moon is tide locked to the earth, meaning its rate of rotate is nearly the same as its orbital period around the earth thus the same face is always facing the earth. There is a warm debate that the Earth may never become tide locked to the moon OR the sun, because it has a moon and of course because of the sun. Currently earth is slowing in its rotation, been doing this for a few billion years - well since whenever the moon appeared And there are several theories on that, and it is a subject of hot debate in some circles. This is important because until we can answer "where did the Moon come from?" we can not answer "What will happen to the Earth/Moon system in future?" The Earth is not a perfect sphere (ball) it bulges around its middle (equator) due to the spin and then it bulged fore and after (toward and away from) the moon - not not exactly for and aft, slightly before the orbit of the moon because the earth is spinning so fast compared to the orbit of the moon. That bulge (tide) is pulling the moon along, causing the moon to slowly gain speed as it tries to catch up with the bulge, thus sending the moon further and further out into a 'higher' orbit. This leads to the moon's influence on earth to weaken slightly, allowing the sun to exert more of its influence (gravity/tide wise) on the earth. The moon is dominated by the earth, but is also affected slightly by the sun, thus we can see a little more of the face of the moon. The moon is not perfectly tide locked to the earth, it slowly 'shakes' its head back and forth ever so slightly due to the influence of the sun, due to the tidal bulge pulling it. Calculations with various variables have demonstrated that the earth should already be tide locked to the moon. --> This Calculation is often used by young earth (creationalists) who insist that if the earth and moon were billions of years old, these calculations demonstrate that the earth and moon would be tide locked to one another. Then there is the theory that the earth will be tide locked with the moon in a few million years. This one is based on assumptions about mass, assumptions about how orbits transfer energy from the rotation of one body (earth in this instance) to orbital velocities (of the moon in this case) and the assumption is that a lot of energy is exchanged at a constant rate. ... and that the tide lock will take place 5 billions years from now, unfortunately after the Sun turns red giant and cobbles up the earth and moon system. This one makes the assumption that as the distance between the two bodies increases the transfer of energy lessens with the square root of the distance - thus the earth's rotational spin is slowing at a slower rate as the orbit of the moon increases gradually increasing at a slower rate over time. Other calculations leave us with a earth moon system moving ever slower but the earth never really getting tide locked to the moon as the Moon and Sun fight to dominate the earth until the sun goes red giant and ends the battle by cobbling up earth and moon. I'm afraid that there is no 'hard' answer to the question, least ways not without far much more observation. Mind until relatively recently (1960's) we thought that Mercury was tide locked to the sun - it should be, but isn't. It has no moon to keep it from not being tide locked. Radar observation showed that Mercury is rotating three times for every two revolutions around the Sun! Its a puzzle, one that is warmly theorized. on one hand we have 'What should be' and then on the other we have 'What is'. Venus is thought to possibly be tide locking to earth in some form or manner. Its orbit bringing it to close approach to Earth every 5 Venusian days - making approximately the same face visible from Earth at each close approach. We do not know if this is just coincidence or if the gravity of the Earth Moon system has affected Venus. If so then we will have to rethink tide locking of Earth to the moon and think maybe a tide lock to Venus. Or most likely due to all of the gravity wells around earth all vying for earth to face them the earth will forever remain out of sync with the moon and never become tide locked to any one body. Orbits, rotations and even trajectories of space craft are NOT following the rules we humans wrote down as 'laws' of physics. The space craft we send to say Mars must have their trajectories fine tuned along the way. Our "laws" of gravity and physics are such that we should be able to shoot a cannon ball at mars (from a very large cannon) and the cannon ball should reach Mars - However we are learning (still) that something else is at work that would make the cannon ball miss its mark. What that "It" is we do not know. That too is warmly debated, theories from a dark companion to theories about us not fully understanding what gravity is (which we do not fully understand what gravity is, not what electricity is, what the weak force is we have theoretical understanding only.) With all of that aside, IF tide locking of the earth moon system takes place it will do so approximately 1.2 billion (yes billion) years in the future (Averaging out the minimal of a handful of millions to 5 billion years). The moon will be orbiting at about one orbit every 40 earth days (as we reckon a day) and a solar day (one rotation earth on its axis) will be about 40 days.
  • In the last 4 billion years, a the length of a day has increased from about 22 hours to 24. It doesn't answer your question, but it gives you a starting point.
  • According to Dr. Pamela Gay, of the Astronomy Cast podcast/website, this will occur in about "a trillion years." I think that the other people who have posted answers have given sufficient detail about how tidal forces cause this to happen, so I will not address that, but you can hear about it in the 17th episode of Astronomy Cast, entitled "Where Does the Moon Come From?" by subscribing, or you can read the transcript on their website, http://www.astronomycast.com/.../ Awesome podcast, can't recommend it highly enough.

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