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Isn't this false?

  1. Dec 13, 2007 #1
    Isn't it the blue light that is scattered LESS than the other spectrums?
  2. jcsd
  3. Dec 13, 2007 #2
    We percieve colours as its absence. A green leaf is due to it emmitting 'all' wavelengths but green.
  4. Dec 13, 2007 #3


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    Staff: Mentor

    The first is true, the second is not. For the sky, consider that if the blue light wasn't scattered, we wouldn't see it coming at us from all directions. For the perceiving colors by their absence, I'm not sure where you get that, but it isn't correct.
  5. Dec 13, 2007 #4
    Fixed it for you.
  6. Dec 13, 2007 #5


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    Science Advisor

    Blue and violet do indeed scatter more. They are high frequency, and behave like hyper children; bouncing all over the place. At short range, like when the sunlight is coming strait down throught the atmosphere, this makes the sky look blue because the blue light is all over the place. At greater depths like sunset (when sunlight is cutting through a lot more atmosphere), the scattering of blue light means that most of it is dispersed before reaching the ground, and the deeper-penetrating low frequencies (at the red end of the spectrum) dominate because they didn't get scattered as much.
  7. Dec 13, 2007 #6
    This is not entirely true. If we refract sunlight we will notice that you don't get a perfect spectrum, some of the lines will be missing, this is true for all stars. However I think the sun has a fairly complete spectrum.

    This is due to the nature of the gas that comprises the star
  8. Dec 13, 2007 #7


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    What frequencies are missing?
  9. Dec 13, 2007 #8
  10. Dec 13, 2007 #9
    Does the blue sky arise mostly from scattering off of relatively static air molecules, dynamic air molecules, or dust particles?
  11. Dec 13, 2007 #10

    Shooting Star

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    "We percieve colours as its absence." This sentence is still there? How did you fix it then :smile:? We perceive green because it's the only one present...
  12. Dec 14, 2007 #11

    Shooting Star

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    Raleigh scattering takes place when 2pi*r/lambda <<1, where r is the characteristic dimension of the particle. For sunlight in air, the scattering particles are the Oxygen and Nitrogen molecules. The intensity of the scattered light is inversely proportional to lambda^4. So, the lower wave lengths, like the violet and the blue, scatter more.

    There is an erroneous idea that dust particles or tiny droplets of water vapour can also cause Raleigh scattering, but their sizes are just too big. For them, the right treatment would be Mie scattering. The white colour of the sky near the sun can be treated according to the latter.
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