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Spectrum of the light

  1. Aug 19, 2009 #1
    we can see very hot fire and we can see cold fire. when fire is very hot it turns blue. now someone told me the spectrum of light from hot sun and cold planet are the same when checking a ray, i ask, how can it be? a ray of light coming from a very hot sun should be in a spectrum dominant by the blue colour
    thank you
  2. jcsd
  3. Aug 19, 2009 #2
    Lets sort a few things out in this post.

    When anything gets hot enough it will start to 'glow' and emit light in the visible spectrum. The hotter it gets, the further up the spectrum the peak emittance will be from deep red to orange, yellow, green, blue and then violet. These are the emitted colors when anything gets hot.

    Now, I own a purple couch. I am not however, afraid to sit on it for fear of being burned to death by temperatures hotter than the sun. The reason why is because even though the peak emittance of the sun is in the yellow, it still emits all wavelengths of light, including purple. My couch is dyed and only reflects light in a wavelength range around purple.

    So there is the importance difference, stars are emitting light because they are hot and glowing, my couch is purple because it is dyed purple and only reflects in that range.

    The planets are not incredibly hot objects that are glowing and emitting radiation. They do however reflect the light from their nearby star, which if very hot could be in the blue or violet range.
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