> through the atmosphere it undergoes elastic (Rayleigh) scattering. If all
> wavelengths were scattered equally then the sky would be simply a bright
> white; instead the scattering goes as the frequency of the light to the
> fourth power. What this means is that the blue end of the visible
> spectrum is scattered more than the red end resulting in a blue sky.
Whoa. So, like, does this have to do with the chemical composition of the atmosphere, i.e. the proportion of nitrogen to oxygen, or is this a law of physics? If Neptune had clear skies, which apparently it doesn't (pretty cloudy in the outer planets) would they be blue-shifted, too?
-- Dennis