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My teacher told me that sun is a black body but after reading at various sites whre they say that sun is not a black body but has black body radiations because it cannot absorb all radiations.


marked as duplicate by John Rennie, user36790, ACuriousMind, Kyle Kanos, Sebastian Riese Dec 21 '15 at 16:45

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    $\begingroup$ The sun is not a black body but the solar spectrum is still pretty well approximated by a black body spectrum. See e.g. physics.stackexchange.com/q/130209 for the actual differences between the real solar spectrum and the black body approximation. $\endgroup$ – CuriousOne Dec 21 '15 at 5:33

Here is the measured radiation from the sun

solar radiation spectrum

It is fitted with a black body curve, at the top of the atmosphere (yellow) and even though it is evident that there are deviations from the theoretical black body, it is still a good approximation.

Generally all bodies radiating are approximated with a black body spectrum. If it fits well, that means that it also absorbs the same type of spectrum, if it fell on it. The deviations are due to the differences stated in the other answer.


It is not a sufficient condition for a blackbody to be perfectly absorbing at all wavelengths. The Sun satisfies this condition pretty well. It must also be in thermal equilibrium.

Whilst for the interior of the Sun, this is a very good approximation, near the surface it is not, because radiation can escape and the temperature changes with depth on a length scale comparable with the mean free path of the photons. As a result it is better to think of the Sun as emitting blackbody radiation from different layers at different temperatures.


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