> Do you know what the odds are against getting a picture of the green flash? Consider this. It only happens in the tropics. Not every sunset produces a green flash. Even when it occurs, most of the people who are watching for it, miss it. I suppose that's because it only lasts for a few hundreths of a second. About nine times out of ten, it happens when the sun is going down behind the ocean. I got it going down behind a mountain on St. Thomas. With odds like that, I don't think I'll even bother to try it again.
> Howard

Here is is
"6. The green flash

So far, dispersion has not been taken into account for the mirages and sunsets simulations, since its effect in the phenomena is negligible. However, every refraction phenomenon includes a certain degree of dispersion, and some atmospheric refraction phenomena provoke a greater dispersion of light, and the green flash is arguably the most spectacular of them all. As our first step towards a complete simulation of the effect, we are going to reproduce the so-called standard green flash, an effect that occurs even in a Standard Atmosphere, taking refraction as a function of wavelength.
The green flash is a very transitory effect, lasting only a few seconds. When the sun is setting, and therefore it is low on the horizon, the path that the light rays travel is longer. Since the atmosphere is denser below than above, the light rays are bent downwards, but because of the index of refraction being a function of wavelength the blue-green rays are bent more than the red ones. The result is that we see a blue-green rim on top of the solar disc, and a red rim at the bottom. Aerosol extinction and Rayleigh scattering [Preetham 2003] eliminate most of the blue from the top rim, thus making the green purer. The red rim at the bottom is usually below the line of horizon and cannot be usually seen, but the effect is nevertheless known as the red flash. Figure 6.1 shows the simulation of the green flash; there is a tiny green rim on the upper half of the solar disk, and a tiny red one on the bottom side, occluded by the horizon. A close-up of the picture allows us to better distinguish the green on top of the solar disk. As the images show, the Standard Atmosphere by itself produces a green flash about ten times smaller than the eye can actually see. It can only be seen by the naked eye when specific special atmospheric conditions that deviate from the standard occur, creating mirages that magnify its appearance