In article <cja### [at] netplexaussieorg>,
 Christopher James Huff <cja### [at] earthlinknet> wrote:

> What Penners is looking for is actually produced by atmospheric 
> scattering, not a lens effect. Unfortunately, the scattering models used 
> in POV peak at an angle of 0 to the light, so you get a glow that's 
> brightest around the source and just falls off from there. The ice 
> crystals that cause this effect scatter light differently, peaking at 22 
> degrees. POV just doesn't have a scattering model that describes this 
> effect. Maybe the scattering intensity curve could be specified with a 
> user-defined function, this would give a great deal more flexibility.

Here's some good pictures of the effect:
http://antwrp.gsfc.nasa.gov/apod/ap000515.html
http://antwrp.gsfc.nasa.gov/apod/ap020114.html
http://antwrp.gsfc.nasa.gov/apod/ap030321.html

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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