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Planets and Stars

  1. Oct 20, 2007 #1
    Since each planet and star has it's own gravity which causes smaller bodies to orbit around them. Will our sun have an orbit around bodies with greater gravity than it?
  2. jcsd
  3. Oct 20, 2007 #2


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    The sun, along with the rest of the solar system, orbits the centre of our galaxy.
  4. Oct 28, 2007 #3
    ...which again is found orbiting in a cluster.
  5. Oct 28, 2007 #4
    ..which is most likely a part of a larger cluster of clusters.
  6. Oct 29, 2007 #5
    .. and so on:P
  7. Oct 29, 2007 #6
    Can it be like that for ever?.
    The linear speed of the Sun is higher than that of the Earth. Then the Milkyway travels faster in rotating the cluster ..and so on.. until something (we may not know) reaches the limit of light speed !!!
  8. Oct 29, 2007 #7
    Are you sure this is what you mean?

    I understand your point here, but obviously no object can reach the speed of light as this would require an infinite amout of energy according to Relativity. Also keep in mind that speed is relative to the reference frame of the observer, so no object can travel with the speed of light relative to Earth.

    Note that when discussing speeds in a cosmic sense, one cannot really use classical terms like km/sec as time is also relative to the speed. If we are to make any sense when using classical terms of velocity, we must at the very least define a fixed reference point in space, as in the case of redshift we assume the Earth to be a stationary point in the Cosmos.
  9. Oct 29, 2007 #8
    The fact that no object can reach the speed of light is something contradict your case: 'and so on', which seems like an unending sequence.
    I find it a little difficult to express my idea just now. But I will come back.
  10. Oct 29, 2007 #9


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    Just to clarify - large bodies orbit small bodies too.

    The Earth is orbiting the Moon just as the Moon is orbiting the Earth. (They both orbit a point part way between Earth and Moon - it's just that this point happens to be inside the Earth's radius.)
  11. Oct 29, 2007 #10


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    There is no correlation between the speeds of bodies orbiting bodies within larger orbiting systems - there's no "progression" of orbital speeds that way. It is simply a factor of the masses and the distances of the objects involved. And there are no objects so massive and so close to each other that their orbits reach the speed of light.

    That being said, black holes do have mass enough that objects getting very close to them will approach relativistic speeds, converting into energy as they fall.
  12. Oct 29, 2007 #11
    I fully understand your question here, and it is quite complex matters we are discussing. The thing is that when I said "and so on" I was refering to super clusters. The question of whether such "magnification" goes on forever depends on the theories of the actual "size" of the Universe, though this is a very bad way of expressing it. If one is a believer of the static model the universe has a finite size, though evidence supports the theory that the Universe is expanding. However, you are correct in that based on the concept of concervation of energy (energy can neither be created nor destroyed) and the equation E=mc^2, the amount of matter/energy in the Universe should be finite so there should be a limit to how great a super(duper:P) cluster can be as it would involve all matter in the Universe as we know it today.

    Also, it was correctly noted that increase in magnification when considering larger and larger gravitational systems of stars and galaxies does not necessarily imply increase in relative speed as that would require a fixed point in a cosmos that seems to be expanding.
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