Composition of the sun and spectrum of light

  • #1
I understand that the sun is made of 91% hydrogen, 8.7% Helium, and 0.3% other stuff. I looked up the atomic spectrum for helium and hydrogen [within the visible portion] and they leave most of the spectrum blank, albeit few lines of colour here and there, yet the white light that reaches us has a full (?) spectrum. Is that 0.3% of the sun responsible for the rest of the colours in white light? How complete is the white light that reaches us? There must be some shades or tones we never see.

Am I wrong in thinking of the sun as a radiating black body? I know that there are nuclear as well as thermal processes occurring, is the fission/fusion responsible for the rest of the visible spectrum?

Answers and Replies

  • #2
To a good approximation, the sun does radiate as a blackbody. Blackbody radiation is a continuous spectrum, and does not depend on the materials that the radiating body is made from. This is because repeated collisions between photons, electrons, nuclei, and neutral atoms in the solar plasma lead to photons which are in thermal equilibrium. Photons which are in thermal equilibrium lead to a continuous blackbody spectrum, which is only a function of temperature. There are absorption and emission lines in the sun's spectrum due to the atoms in the sun, but they cause only a relatively small deviation from the blackbody spectrum

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