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Question about Moon's Orbit

  1. Jun 10, 2010 #1
    For the moon to stay in orbit and not crash down into Earth, it must have sufficient tangential velocity. I'm wondering where/how it initially got the energy to reach this tangential velocity.

  2. jcsd
  3. Jun 10, 2010 #2


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    Nobody's really sure how the moon formed or exactly why it got put into the orbit it did. The leading theory, I think, is that there was some kind of impact that split it off from the Earth, but there's no conclusive evidence.

    What we do know is that the moon does have sufficient tangential velocity to stay in orbit. So no crashing is in the foreseeable future.
  4. Jun 10, 2010 #3


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    Yes, I believe an impact from a Mars-sized planetoid is the prevailing theory.

    Note to the OP: are you only interested in the Moon specifically? The Moon's origin does not help you understand the orbital veolcities of any other moons in the Solar System.
  5. Jun 14, 2010 #4
    Actually I'm interested generally on how orbits are formed, for instance how is Earth's orbit around the sun formed? Generally what is giving energy to extra-terrestrial objects to allow them to move at enough velocity to gain an orbit.
  6. Jun 14, 2010 #5


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    The Solar System including Sun and Earth formed as a unit, coalescing from a disc of dust and gas. The orbital velocity of almost all the planets in the SS was intrinsic to that initial rotating disc.

    Pluto, being an exception, was possibly captured after the SS was formed.

    There are lots of assumptions here. They don't gain an orbit - they start as a rotating discs of dust and gas. They got their initial energy ultimately from the Big Bang, then later as they gathered under gravity, they retained their angular momentum (like an ice skater pulling in her arms).
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