Astrophysics (index)

### Opacity

(Attenuation Coefficient)
(a measure of opaqueness of a material)

 Opacity (or Attenuation Coefficient) is a measure of opaqueness of a material, i.e., to what degree light is absorbed as it passes through. As used in astrophysics, the term specifically means the rate at which the density of a material reduces the Intensity of a beam of light passing through. It varies by Wavelength. Opacity can occur at values from 0 to ∞. It decreases the intensity as follows (given uniform opacity and density): ```Id = I0e-κρd ``` I0 - intensity before passing through the substance. Id - intensity after passing through distance d. κ - opacity. ρ - density of the material. d - distance traveled through the material. The opacity and intensity in this equation can be subscripted by ν to specify the intended wavelength. Since the opacity varies by wavelength, some assumption regarding the spectrum must be made to define an opacity applicable to more than a single wavelength. The Rosseland Mean Opacity is an example. (physics,EMR,optics,measure) http://en.wikipedia.org/wiki/Opacity_(optics) Referenced by: Greenhouse Effect Kramers' Opacity Law Optical Depth (τ) Rosseland Mean Opacity Equation of Radiative Transfer (RTE) Synthetic Field Method (SFM) Stellar Structure

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