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  • #16
    Originally posted by gunnut View Post
    Sir, the moon is moving away from earth because it carries too much energy. Orbits decay (I assume you mean our artificial satellites) due to their friction with air. Most satellites are too low to be completely free of the atmosphere. Think about it, what is "escape velocity?" It's the speed to break free of the gravitational pull of a body. A velocity higher than that will break free. A velocity lower than that will not. Moon has just slightly higher velocity than the escape velocity of earth.
    Not entirely accurate. The Earth-Moon system began its existence with a certain total amount of angular momentum L (think of it as kinda-sorta the total rotational and revolutionary "speed" of both bodies) and it MUST be preserved. As the various tidal and frictional forces act on the Earth-Moon system to slow them down, the moment arm of the system must increase in order to preserve the total value.

    Here, think ice skater moving arms in and out after the spin starts - arms in - speeds up, arms out, slows down.

    So basically, the Earth-Moon system must extend its orbital arms because it is slowing down. Entropy's in there too - energy loss in any orbital system is NEVER zero, so over time all "close" orbital systems - solar systems, galaxies, etc. - will all drift farther and farther apart over many billions of years, eventually spreading out into a zero energy state at infinite distances from each other.

    -dale

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    • #17
      Although this is on a much smaller than galactic or universal scale, could the push of the Big Bang itself have anything to do with the moon getting farther away from earth? We know (or believe we know) that the universe is expanding, but also that the entire fabric of the universe is expanding. Wouldn't that also include the fabric of the universe, "minuscule" as it may be, between the earth and the moon also expanding?
      Meddle not in the affairs of dragons, for you are crunchy and taste good with ketchup.

      Abusing Yellow is meant to be a labor of love, not something you sell to the highest bidder.

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      • #18
        Originally posted by bigross86 View Post
        Although this is on a much smaller than galactic or universal scale, could the push of the Big Bang itself have anything to do with the moon getting farther away from earth? We know (or believe we know) that the universe is expanding, but also that the entire fabric of the universe is expanding. Wouldn't that also include the fabric of the universe, "minuscule" as it may be, between the earth and the moon also expanding?
        Well if thats the case the earth must be moving in the opposite direction ,,shit we gonna crash into mercury ?

        Has anyone besides myself , Dalem n Chogy looked at the vid ??

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        • #19
          dale,

          Why would L be a constant? Both bodies are moving and there should be an energy loss, unless there is another source.
          No such thing as a good tax - Churchill

          To make mistakes is human. To blame someone else for your mistake, is strategic.

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          • #20
            My understanding is that L is not constant, but very nearly so. The only mechanism for energy loss in the system would be friction forces between the moon and earth's atmosphere and between earth and the interstellar medium / solar winds. Either way, friction forces which would be disastrous for a tiny man made satellite are negligible for objects with the mass of the earth and moon. Which is not to say they don't exist, just that the effect they will have over the lifetime of the earth is minor. Our sun will go all red giant and obliterate us long before our orbit has any chance of decaying due to friction.

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            • #21
              Originally posted by Doktor View Post
              dale,

              Why would L be a constant? Both bodies are moving and there should be an energy loss, unless there is another source.
              I dunno. A constant's a constant. :) If they ever taught us why in this case then I don't remember. Why is the speed of light a constant? That's just the way it is.

              You're correct that there is going to be energy loss in the system, but in an ideal laboratory setup with two uniform bodies spinning and revolving about each other in a perfect vacuum, in theory there is no energy leaving the system so everything should remain constant forever.

              -dale

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              • #22
                Originally posted by guicho80 View Post
                My understanding is that L is not constant, but very nearly so. The only mechanism for energy loss in the system would be friction forces between the moon and earth's atmosphere and between earth and the interstellar medium / solar winds. Either way, friction forces which would be disastrous for a tiny man made satellite are negligible for objects with the mass of the earth and moon. Which is not to say they don't exist, just that the effect they will have over the lifetime of the earth is minor. Our sun will go all red giant and obliterate us long before our orbit has any chance of decaying due to friction.
                Tidal forces between the Earth and Moon are a big factor - note the tidal locking which has already occurred - that would have drained a significant amount of energy from the system. The Earth is not a uniform body - frictional forces between its various layers as they spin - core, mantle, crust, atmosphere - is a steady background drain.

                -dale
                Last edited by dalem; 21 Aug 12,, 19:26.

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                • #23
                  Originally posted by dalem View Post
                  I dunno. A constant's a constant. :) If they ever taught us why in this case then I don't remember.
                  Weren't you curious? I can imagine the fury of the professor in my school if such question was asked, but still.

                  Why is the speed of light a constant?
                  Because the light isn't Bolt

                  That's just the way it is.
                  Fair enough. The higher authority said so.

                  You're correct that there is going to be energy loss in the system, but in an ideal laboratory setup with two uniform bodies spinning and revolving about each other in a perfect vacuum, in theory there is no energy leaving the system so everything should remain constant forever.

                  -dale
                  The thing is the universe is not a perfect lab with a perfect vacuum and the distance between those bodies is not constant, so why would everything else be?

                  I am not pushy, just curious.
                  No such thing as a good tax - Churchill

                  To make mistakes is human. To blame someone else for your mistake, is strategic.

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                  • #24
                    You are correct sir. One of these days I will stop conflating conservation of momentum with conservation of energy.

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                    • #25
                      Originally posted by Doktor View Post
                      Weren't you curious? I can imagine the fury of the professor in my school if such question was asked, but still.


                      Because the light isn't Bolt


                      Fair enough. The higher authority said so.


                      The thing is the universe is not a perfect lab with a perfect vacuum and the distance between those bodies is not constant, so why would everything else be?

                      I am not pushy, just curious.
                      No probs, and, sure, of course I was and still am curious. But those kinds of questions need lots and lots of learnin' just to ask correctly, let alone to understand the answers. The really mind-bending stuff is in cosmology and quantum mechanics and is very difficult to discuss in words - I can barely scratch the surface myself and I'm better-equipped than the average layman.

                      -dale

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                      • #26
                        Warrabout the shift on the moon ????????????????????? Crater at 5 , one month later at 3 .

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                        • #27
                          Are both observations made with the same telescope? From what I have gathered, a celestial object's perceived orientation in the sky can vary depending on the type of telescope mount used.

                          Solar Observing: Parallactic Angle

                          Also, even though the moon is tidally locked with the earth, it does oscillate slightly with relation to the earth. So, over time, we get to see slightly more than the half of the surface you would expect to see if its orientation with the earth were rigidly locked. I expect one or both of these would account for the discrepancy in the video. After all, its not like the crater is shifting about with relation to other surface features.

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                          • #28
                            But it is , it was done with a camcorder , the moon wherever looks the same ,c,mon lads look at the vid :slap:

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                            • #29
                              Here ya go tankie. This should clear up the matter:

                              Near side of the Moon - Wikipedia, the free encyclopedia

                              I direct you to the part about the moon's perceived orientation. Specifically, the bit about southern latitudes, which is where the dude in the video made his observations.

                              In mid southern latitudes (South America, South Pacific, Australia, South Africa) the Moon rises in the east with its southeastern limb up (Mare Nectaris), it reaches it highest point in the north with its south on top, and sets in the west with its southwestern limb (Mare Humorum) on top.
                              So even though the moon always presents us with roughly the same side, its orientation as seen by an observer on earth WILL vary depending on the observer's geographic location, and also apparently, with the moon's position in the sky. Nothing sinister happening here. :)

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                              • #30
                                Originally posted by guicho80 View Post
                                Here ya go tankie. This should clear up the matter:

                                Near side of the Moon - Wikipedia, the free encyclopedia



                                Thanks , ;) but its shifting much more than wiki shows

                                http://www.youtube.com/watch?v=9oiHRUw1KoM


                                http://www.youtube.com/watch?v=zZHKf...eature=related
                                Last edited by tankie; 22 Aug 12,, 15:07.

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