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Black Bodies :S

  1. Jun 5, 2012 #1
    Well, am an Alevel student... Edexcel.. I just find quantum physics a really really confusing topic.. My question is particularly in black bodies. If we consider the sun as a black body, where did the radiations of the sun initially come from. I don't mean the emitted radiation we see, i mean the original radiation which it absorbed. Secondly, what do white lines on a spectrum means and why yhe spectrum doesn't reach beyond visible light.. I am new to this forum so forgive my way i've posted my doubt.. Thanks :D
  2. jcsd
  3. Jun 5, 2012 #2
    Guys.. I really need help cs am having a test in a couple of weeks and i understand nothing!
  4. Jun 5, 2012 #3


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    The Sun gets its energy from fusion at its core. I suppose you can think of it kind of like the outer layer of the sun "absorbing light" from the core if it helps you conceptualize a little better (of course, don't take it too literally, there's a complex energy transport problem from the inner to outer regions of the sun which involves a lot more than just radiation transfer).

    I don't know what you mean by "white lines" on a spectrum. What are you referring to? Are you talking about absorption and emission lines from the Sun? Also, what do you mean "the spectrum doesn't reach 'beyond' visible light"? The Sun radiates at all frequencies, it just mostly radiates in the visible because those are the frequencies corresponding to the peak in the black-body curve for the Sun (it is probably for this reason that we evolved to see visible light).
  5. Jun 5, 2012 #4
    Dude, i owe u.. Thanks for help.. Here are my current doubts... What is a peak wavelength.. Like, a black body emits energy of all wavelenghts but y is there a peak at a particular one.. Secondly, it was mybad, i just wanted to know the absorbtion spectrum..
  6. Jun 5, 2012 #5


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    The black body radiation gives a peak, this was one of the fundamental results of Planck and his distribution. To really understand the reason why there's a peak, one needs to understand the Planck distribution.

    For example, before Planck, Rayleigh had a "black body solution"; however, it ran into the Ultraviolet catastrophe. It was Planck who solved this problem by "quantizing" the energy (somewhat arbitrarily) of the atoms in a black body.

    The absorption spectrum of the Sun is dictated by what molecules and atoms are in the Sun's atmosphere. Certain molecules/atoms will absorb certain frequencies of light. When the light from the Sun's photosphere is being transported through its atmosphere, some of it is absorbed by these molecules/atoms at those specific frequencies. There's not much more to it than that.
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