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Why is the sky blue?

  1. Oct 24, 2005 #1

    Mk

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    What are some reasons that the sky is blue?
     
    Last edited: Oct 24, 2005
  2. jcsd
  3. Oct 24, 2005 #2
    It is the way the light bends as it passes through the atomosphere. (Or somthinkg like that)
     
  4. Oct 24, 2005 #3
    http://en.wikipedia.org/wiki/Rayleigh_scattering

    The amount of scattering depends on the frequency of the light. Blue light, having a higher frequency, scatters more than lower frequencies (Which pretty much pass straight through the atmosphere). This scattering of blue light more than the other visible frequencies results in us seeing the sky as blue.
     
  5. Oct 24, 2005 #4

    Mk

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    So is air blue? Water is generally blue, the greater the quantity the bluer it seems to get, is air the same way?
     
  6. Oct 24, 2005 #5
    Water itself isn't blue, really. Hey, it's the liquid we drink all the time!
     
    Last edited: Oct 24, 2005
  7. Oct 24, 2005 #6
    The reason water is blue, is because of the reflection of the blue sky on the water... thats all... water isn't blue...
     
  8. Oct 24, 2005 #7

    FredGarvin

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    Why is the sky blue? If it were green we wouldn't know where to stop mowing.
     
  9. Oct 24, 2005 #8
    Answer

    This peeling off of the lower frequencies in the spectrum (blues) is called Rayleigh scattering.
     
  10. Oct 24, 2005 #9
    No, actually Rayleigh scattering is at least partially responsible for water being blue too. The deeper you go in water the more of the spectrum is bounced out. At 33 feet you've lost the color red. At 66 feet you've lost orange.

    This is the reason divers need flashlights that use the whole spectrum. Otherwise they would misidentify objects.
     
  11. Oct 24, 2005 #10

    Chi Meson

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    Water absorbs radiant energy ("light"). Water will more quickly absorb light with longer wavelengths. Water absorbs microwave and infra red wavelengths almost immediately, and visible red relatively quickly. If the red part of the spectrum is absorbed, then the gree/blue colors remain.

    gree-to-blue light is going to be scattered in the upper layers of water, so when viewed from above, water appers to be green-blue.

    The sky is blue due to scattering entirely. The blue light from the sun hits air molecules and is absorbed mometarily, then re-emitted in a random direction. REd light does not get so easily absorbed/re-emitted and thus maintains more of a straight line path, hence orange-red sunsets.

    The notion of water reflecting the sky is an oft-quoted misconception that is unfortunately still taught in grade-school "science" textbooks.
     
  12. Oct 24, 2005 #11

    Mk

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    So is water blue because water is blue? Or is it scattering? Or something else?
     
  13. Oct 25, 2005 #12

    Tide

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    An important factor in the sky being blue is the presence of fluctuations in density and temperature (i.e. nonuniformity). Without such fluctuations the the Rayleigh fields will be cancelled at every point.
     
  14. Oct 25, 2005 #13

    GENIERE

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    You made me spill my coffee.:biggrin:
     
  15. Oct 25, 2005 #14

    Mk

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    Did it scatter? Or was it something else?
     
  16. Oct 25, 2005 #15

    dextercioby

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    The best explanation (also with numerical values to get an idea) one can find in any of the 3 editions of J.D.Jackson's text on CED.

    Daniel.
     
  17. Oct 25, 2005 #16

    Chi Meson

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    Things are the color that they are due to teh frequencies of light that emerge from them. Ignoring whatever might be in the water (algae, mud, red tide etc) oceans are gree-blue because that is the light that scatters back out of the oceans.
     
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