Why is the sky blue ?

Discussion in 'Earth Science' started by Zarkov, Sep 1, 2003.

  1. Zarkov Banned Banned

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    Good work guys !

    >> Usually this sort of thing is done to look at the more interesting types of scattering, like Raman scattering, but the Rayleigh-scattered light will show up just fine.

    Has any paractical observations been done on scattering from oxygen or nitrogen gas ??

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  3. Nasor Valued Senior Member

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    Re: Good work guys !

    Yes. You can actually determine the density of a nitrogen sample by looking at how much it scatters light; the more dense the sample, the more scattering you get. This effect is sometimes exploited in sophisticated wind tunnels. Engineers will measure the scattering from the atmospheric nitrogen in the air as it moves through the wind tunnel to examine how the air's density changes at various points as it flows over the object in the tunnel.
     
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  5. Zarkov Banned Banned

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    Thanks, very interesting.

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  7. Nasor Valued Senior Member

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    Why do you think the sky is blue?
     
  8. Zarkov Banned Banned

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    OK, lets discuss the second half.

    Water is blue, liquid oxygen is sky blue..... The colour of water can only be viewed by the eye when it is thick, eg looking into several meters of sea water. This can also be seen easier in solid water, ice... the blue of ice caves etc.

    The sky is a thick layer of gas, nitrogen is colourless as is the other gases ( the solid/liquids are colourless). The amount of oxygen gass in the atmosphere, given it's thickness, would also appear blue IMO.

    Mie scattering alters this colour perception because at the edges it "brightens the sky" and reflects white light to fade the sky, or highlights the Rayleigh scattering through the smoke pollution (thicker atmosphere) to yeild reddened edges.

    So to the discussion !!

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  9. Taffy Wake Registered Senior Member

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    hey there zarky my love!

    um, i thought liquid oxygen wasn't blue...but then i could be wrong....oops, or you could be

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  10. Nasor Valued Senior Member

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    I don't understand what you're saying. Water being blue isn't related to the sky being blue. It's caused by completely different effects. Water filters out red light, so the light coming out of it tends to look blue. The sky is blue because the atmosphere scatters blue light toward the earth. It's caused by both the nitrogen and the oxygen in the atmosphere.
     
  11. Zarkov Banned Banned

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    TAFFY WAKE... YEEEEE YAAAA WOOOWW

    >>hey there zarky my love!

    Hi Taffy, great GREAT to know you are still "out there"... I miss your zanny glow and your sexy arse !!!

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    Nasor...
    >> Water filters out red light, so the light coming out of it tends to look blue.

    It is the oxygen that is doing this, pure oxygen does this as well, in fact even better !!

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  12. Taffy Wake Registered Senior Member

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    ah zarky, good to see that after all these years you're still sticking to your theories schweetie. one of these days i'll get off my arse and try and absorb what you're saying and why it gets up the nose of so many others...but till then good on ya.

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    but i still reckon liquid oxygen is not blue and the sky is blue from raleigh scattering. in this i can only say i accept it on faith, not so good from a committed atheist but i love anachronism.

    i tell you what i do have the energy to read...about the pyramid water thing...if it isn't too long.

    start a new thread about that and i'll read with gusto,
    taff
     
  13. Zarkov Banned Banned

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    Heeheee, you bitch !! You know how to get a guys attention, damn women. >

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    ))

    Pyramid water, these guys would freak out.

    To start off, in what stream should I piss in the corner... Haa haa, couldn't even talk about "push" verus "pull" without cries of foul !!

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  14. Nasor Valued Senior Member

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    Re: TAFFY WAKE... YEEEEE YAAAA WOOOWW

    You're wrong about this. It is not the oxygen its self that makes water blue, but vibrations within the molecule along the bond between the hydrogen and oxygen atoms.

    Proof: D2O (water that has deuterium instead of hydrogen, also called heavy water) is not blue because the heavier mass of deuterium causes the molecule to vibrate differently and absorb light in the infrared region, rather than red. D2O is not blue, even though it has the same oxygen content as normal water.
     
  15. Zarkov Banned Banned

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    You are convincing Nasor. Good work.

    What do you consider Rayleigh scattering to be due to ?

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  16. MRC_Hans Skeptic Registered Senior Member

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    Raleigh scatering is due to diffraction. A light wave interacting with the edge of a particle is bent. After a number of interactions its direction is basically random.

    Now for your claim that oxygen colors the sky:

    Go out on a sunny day and stand in a shadow (with the sky visible). Is it dark there? No, because there is a lot of light coming from the blue sky. What is the source of that light? It is the sun. If the light from the sun is gone, like at night or during a solar eclipse, the sky is black.

    How can light from the sun reach you from other parts of the sky? Because it is being scattered. But the blue color, can't it come from filtering through oxygen? No, because the color would depend on how far the light travelled through air, thus the sky would be less blue directly overhead. This is not what we observe.

    Hans
     
  17. eburacum45 Valued Senior Member

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    I have to admit that when I saw liquid oxygen in the lab, (it is blue, by the way) the same thought crossed my mind; perhaps the sky is blue because oxygen is blue.
    However, I believe the Rayleigh scattering explanation is correct,
    and the blue colour of LOX is a coincidence.

    Look at blue Neptune, for instance; no oxygen to speak of, but a pretty colour none-the-less.
     
  18. Zarkov Banned Banned

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    >> How can light from the sun reach you from other parts of the sky?

    I do agree with mie scattering, this is occurring everywhere..

    As for H20 and O2 being blue and D20 not being blue, I don't know.. That is an interest !!

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  19. MRC_Hans Skeptic Registered Senior Member

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    Come on! Stop trolling and show your colors (pun intended). Explain your thesis and show how it fits observations. So far, your explanation is contradicted by what anybody can observe on a clear day.

    Hans
     
  20. thed IT Gopher Registered Senior Member

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    The Aurora is due to charged particles from the Sun being accelerated by the Earths Magnetic field, by synchrotron acceleration, and giving off photons. The different colours are then given by O, N and other gases being excited by the charged particles. At least, if memory serves.
     
  21. Nasor Valued Senior Member

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    It's caused by interactions between the electric field of the photons and the electric field of the electrons in the molecules. See http://scienceworld.wolfram.com/physics/RayleighScattering.html for more information.
     
  22. Zarkov Banned Banned

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    >> No, because the color would depend on how far the light travelled through air, thus the sky would be less blue directly overhead. This is not what we observe.

    A valid criticism, but the intensity of the blue varies from day to day...

    The Sun's rays would be reasonably constant.....

    Therefore the process is somewhat independant of the Sun.

    The pale sky could be O2 or background Rayleigh scattering ?

    The intensification maybe due to water content ?

    OR one may conclude that the level of O2 in the atmosphere varies ??

    The truth usually lies in the compromise.

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  23. MRC_Hans Skeptic Registered Senior Member

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    Hans
     

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