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Thread: What color is the sun?

  1. #31
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    Quote Originally Posted by tocket View Post
    Do dust particles really contribute significantly to changing the spectral distribution?
    Yes. There is an experiment that most kids see in their first year physics class. The instructor shines a bright lamp through a tall, narrow tank of water. The light appears yellowish-white. Then he adds some chloride salts and a bit of silver nitrate. The silver nitrate grabs the chloride ions, creating a precipitate that begins to turn the water turbid. As this progresses, the filtered light will first appear blue (just like the sky), but after a few seconds it will rapidly shift through orange and red before becoming opaque. The lesson here is that increased particle size changes the wavelength that is scattered.

    As for Xytrell's question about why there aren't any green stars, the answer can be found on the same bad astronomy blog entry that the black-body radiation graph was lifted from. In short, bodies hot enough to peak their emission in the green portion of the spectrum are also radiating at lots of other wavelengths, and the combination of those wavelengths is interpreted by our (imperfect) human color vision as white.

    For the record, this is also why the sun looks white, even though the emission peak is closer to yellow. Our color vision is not perfect (by any means).

    Adam
    Last edited by buffo; 06-15-2009 at 07:51. Reason: fixed link

  2. #32
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    But are there enough nanometer-sized particles in the air to actually significantly change the SPD? From what I can tell most losses in the atmosphere seem to be from Rayleigh scattering by atoms and molecules and wavelength independent Mie scattering from large particles.

  3. #33
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    I think we must also consider the latitude in the colour temperature prediction. Also the colour changes with cloud cover, on a cloudy day the light is very white, yet on a clear sunny day it looks more yellow. To me that is.
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  4. #34
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    Quote Originally Posted by buffo View Post
    bodies hot enough to peak their emission in the green portion of the spectrum are also radiating at lots of other wavelengths, and the combination of those wavelengths is interpreted by our (imperfect) human color vision as white.
    So why is it when I have a larger ratio of green in my RGB mix than either red or blue, it appears green and not still white?

  5. #35
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    Quote Originally Posted by Xytrell View Post
    So why is it when I have a larger ratio of green in my RGB mix than either red or blue, it appears green and not still white?

    Because with your RGB you are causing a hump in the combined spectrum at the green wavelength, when a black body radiator heats up; it starts to emit in gradually higher and higher frequencies (shorter wavelength), but the emmision of lower wavelengths are still there in relative proportion.
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  6. #36
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    I just went outside and looked at it...it is black.
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  7. #37
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    I stand corrected and enlightened as a result - isn't the internet great lol

  8. #38
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    Quote Originally Posted by Laserman532 View Post
    I just went outside and looked at it...it is black.

    D65 or regular?
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  9. #39
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  10. #40
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    Quote Originally Posted by madgadget View Post
    You can get plenty of green fireworks. That's black body radiation.
    Sorry the green and blue in fireworks is a ionic band with energy transfered to a electron orbit via a donor ion. Usually a chlorine ion.

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