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Observing light

  1. Mar 19, 2010 #1
    If you were on the moon looking at the earth, why can you not see light between the earth and the sun? Same goes for heat. Why is the space between the sun and the earth so cold. Does light and heat only exist once it interacts with something else?
    If light is a particle wouldnt the particles spread out to the point where you would have no idea what of where an object is. If light is a wave wouldn't we see sunlight cover everytinhg in every direction?
  2. jcsd
  3. Mar 19, 2010 #2
    Interesting question. If light was shining through a volume of space with no identifiable source, thus causing you to not be able to see anything...that would be kind of funny. It could be because light is characteristic of a source. At the moment, I think the only thing we know that light interacts with other than itself (in a sense) is matter.
    Last edited: Mar 19, 2010
  4. Mar 19, 2010 #3


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    There is nothing to scatter the light back at you. Think of light rays. The light rays that go towards Earth only hit Earth. They don't want to come to you on the Moon.

    You can't "heat" empty space. There is nothing to "heat". There can be background radiation, like the CMBR, but that's only about 3K. The only reason we get to see the CMBR everywhere is that the big bang happened "everywhere".
  5. Mar 19, 2010 #4
  6. Mar 19, 2010 #5


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    They can't. Your eye can only detect photons that hit it and since photons travel in a straight line....
    Correct - unless they hit something and scatter toward you.
    That doesn't make sense...which is probably why it is wrong!
  7. Mar 28, 2010 #6
    I am still curious how light travels from a distant star to our eyes. If light was a particle wouldnt the particles be spread out to much by the time it reached us? if it was a wave wouldnt we see a wall of light and not be able to tell where the star is? Wouldnt it be like seeing a wave from the shore, you would not be able to tell where the wave originated?
  8. Mar 28, 2010 #7

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    It does. That's why stars are dim, and that's why you can see them anywhere - the light ahs spread out. But not too much to see.
  9. Mar 28, 2010 #8
    Only those photons or waves reach our eye that are exactly in a line to the star (or almost a line due to refraction). But even then they need to be focused by our eye in order to see the star sharply. Also, I'm not sure the light waves are the same as sea waves or sound waves (circular or spherical waves). I think the wave property manifests itself as a fluctuation of force. I'm not a professor though, hopefully one of them will care to help you out.
    Last edited: Mar 28, 2010
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