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Rosseland mean opacity

(Rosseland mean)
(a useful weighted average of opacities at all the wavelengths)

The Rosseland mean opacity (or simply Rosseland mean) is a weighted average (across frequency) of the opacity of a material, e.g., gas or plasma through which electromagnetic radiation is passing. It is designed to be useful for models that try to do a single calculation covering all wavelengths rather than treating each wavelength individually, and given the complexity of the effect of a gas on a spectrum, to make such models tractable. It is:

 1    1  ∞ Iν
——— = — ∫   —— dν
<κ>   I 0   κν


A model stellar atmosphere using this short cut is called a gray atmosphere.


Referenced by:
gray atmosphere
mean molecular weight (μ)
optical depth (τ)
equation of radiative transfer (RTE)