A question about the sun and blackbody

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Discussion Overview

The discussion revolves around the reasons why the spectrum of sunlight resembles that of a blackbody. It explores the theoretical and physical principles behind this similarity, focusing on concepts such as blackbody radiation, the sun's characteristics, and the processes occurring within its atmosphere.

Discussion Character

  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the sun is a reasonable approximation of a blackbody due to its size and temperature.
  • Others argue that the observed wavelength distribution of photons from the sun aligns with that of a blackbody, particularly when considering total energy.
  • A participant mentions that the sun's emission is dominated by Planck distributed radiation, which overshadows line and band emissions.
  • Another explanation suggests that the continuous spectrum radiation from the sun is produced deeper in the photosphere, where absorption and reemission processes reach equilibrium, akin to a blackbody scenario.
  • It is noted that very little radiation is absorbed or contributes to emission lines, highlighting the role of Fraunhofer lines.

Areas of Agreement / Disagreement

Participants generally agree on the approximation of the sun as a blackbody and the mechanisms contributing to its spectrum, but the discussion does not resolve all nuances regarding the details of these processes.

Contextual Notes

Limitations include the dependence on definitions of blackbody radiation and the specific conditions under which the sun's spectrum is analyzed. Some assumptions about the processes in the photosphere remain unexamined.

wenty
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Why is the spectrum of sunligt similar to that of a blackbody?
 
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wenty said:
Why is the spectrum of sunligt similar to that of a blackbody?

Because the sun is a reasonable approximation of a blackbody.
 
Because the observed wavelength (or frequency) distribution of photons from the Sun is the same as that of a blackbody, to the zeroth order (using total energy as the measure).
 
Because the sun is a big, hot thing, and the Planck distributed radiation swamps the line and band emissions.

Jerry Abbott
 
A little more detailed explanation is that most of the emmision from the sun is continuous spectrum radiation produced deeper in the photosphere where the photons are absorbed and reemitted about equally, so that the two processes are in equilibrium, which is what occurs in a blackbody. Very little of the radiation is absorbed (fraunhofer lines) or added to produce emission lines.
 
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