Are Stars Perfect Black Bodies or Just Approximations?

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Discussion Overview

The discussion revolves around whether stars can be considered perfect black bodies or if they are merely approximations. Participants explore the implications of black body radiation in the context of stars and other cosmic phenomena, touching on theoretical and observational aspects.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants propose that the spectrum of a star is approximately that of a black body.
  • Others question the meaning of "approximately," asking if any completely black body exists or if all are approximations.
  • A participant suggests that the cosmic microwave background is a better approximation of a black body than a star.
  • There is mention of Hawking radiation as a theoretical black body, although it has not yet been observed.
  • One participant argues that no perfect black body exists, stating that black bodies are a limiting case of thermodynamics and that imperfections in black body spectra are significant, particularly due to absorption lines from gas above a star's photosphere.

Areas of Agreement / Disagreement

Participants express differing views on the existence of perfect black bodies and the nature of approximations in black body radiation, indicating that the discussion remains unresolved.

Contextual Notes

Limitations include the dependence on definitions of black bodies and the assumptions regarding thermodynamic equilibrium, as well as the unresolved status of certain theoretical concepts like Hawking radiation.

werner heisenberg
Can somebody answer my question in a unique word? Are stars considered black bodies?
 
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the spectrum of a star is approximately black body.
 
What does 'aproximately' mean? does any 'competely' black body exist somewhere or all black bodies are aproximately black bodies?
 
approximately means not exactly. the cosmic microwave background is better approximated by a black body than a star. Hawking radiation, although not yet observed, is also black body.

I don't think there exists any "perfect" black body.
 
werner Heisenberg said:
What does 'aproximately' mean? does any 'competely' black body exist somewhere or all black bodies are aproximately black bodies?

Blackbodies are a limiting case of thermodynamics. In that equilibrium calculations only truly apply in the limit of an infinite number of particles settling for an infinite amount of time, no blackbody will be perfect. However, the primary "imperfections" in most blackbody spectra are of a larger magnitude than this. In the case of stars, the imperfections are mostly absorption lines from the gas sitting above the photosphere.
 

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