The Indo surfer’s sunset green flash:
(I tried to find a green Sprite bottle for the teetotaleer’s green flash…)
I think like most tropical surfers on boats at sea, I’ve seen a bunch of genuine green flashes over the years, although they are more accurately called “green specks” during the second or two just after the sun has gone below a sharp, clean, cloudless horizon.
Here’s a brief explanation of the science behind it from the Mount Wilson Observatory
The green flash is an atmospheric refractive phenomenon where the top edge of the Sun will momentarily turn green. It is seen rarely by the naked eye, primarily because it requires specific conditions to occur, but also because it requires the observer to know what to look for. Despite the name, there is no “flash”; the event only lasts from a fraction of a second to at the longest, a few seconds.
The basic cause for the green flash is that refraction bends the light of the Sun. The atmosphere acts like a weak prism, separating the light into different colors. Bluer light is bent more strongly than red light. However, the amount of refraction even at the horizon is quite small: only a few seconds of arc (one second of arc is 1/3600th of a degree). This effect is magnified by the atmosphere itself. Layering in the atmosphere causes an effect similar to a horizontal cylindrical lens: the separation of the color bands is exaggerated in the vertical direction, so that the separation can be up to several minutes of arc.