I agree that the function of spectral intensity depending on position and direction would be interesting. It's clearly non-trivial to calculate: it's a 5-dimens

I agree that the function of spectral intensity depending on position and direction would be interesting. It's clearly non-trivial to calculate: it's a 5-dimensional field for any given wavelength, so the whole thing is a 6-dimensional function. I wonder if it could be represented and simulated in terms of a finite element system. Otherwise there's always the myriad ways of solving the rendering equation. :-) I'd love to know what physical effect causes this red haze. As you say, if methane weakly absorbs red light, we should be seeing green/blue, not red. A cursory search of mine also revealed the Titan example, but I couldn't find anything terribly specific linking it to methane in particular. (Titan appears orange, methane is present in its atmosphere; it's not clear to me if and how the two are connected)