This is what defines the visible edge of a star, since it is at a few optical depths that the star becomes opaque.
32.
To achieve emission, the layer of at least one or two optical depths of the gas has to be compressed to sufficient temperature.
33.
The range of temperatures and water vapour concentrations over which the optical depth computations are valid depends on the training datasets which were used.
34.
The likelihood of shock ionization in the GPs combined with the Lya emission suggests a possible explanation for low optical depths in the GPs.
35.
Commonly used definitions of the radius in such cases include : a temperature radius; an optical depth radius; and a transformed radius.
36.
A distance equal to one optical depth is the thickness of the absorbing gas from which a fraction of 1 / e photons can escape.
37.
The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2 / 3:
38.
See Wikimedia and www . forrestmims . org for 25-year charts of total ozone, total water vapor and optical depth ( haze ).
39.
Here we have set the lower limit of \ tau to zero, which is the value of optical depth at the surface of the atmosphere.
40.
Some climate models tend to assume that aerosol optical depth increases linearly with the quantity of erupted sulfur and tend to thus overstimate the climate effects.
