12/30/2004: Green flash at sunset

[cweekly]

capnhowdy: I understand the color bit, but I wonder why the edges are so rough.

that roughness -- specifically the striations -- are caused by different levels of light absorption/refraction at different heights in the atmosphere. by the time you see those, the sun is actually below the horizon(!) but you see the light from it bent/redirected through the atmosphere at slightly different levels according to altitude. the density of matter in the upper levels of the atmosphere is less than in lower zones: also, rather than being a steady gradient, the atmospheric zones are delimited at fairly distinct altitudes. thus the stripes in the setting sun are a distorted representation of these atmospheric pressure levels.

another note bene: this is also related to the reason sunsets are so pretty: the red and orange hues are caused by the lengthening of ths sun's rays as the sunlight travels further, it's in effect being stretched, and longer wavelengths are more red, while shorter ones are more blue. (this "redshifting" is an example of the doppler effect, which also explains why car engines sound higher pitched as they race towards you then suddenly lower as they recede)

that's the gist anyway (from memory),someone else may post a more technically precise answer

happy new year
-cweekly

ps I almost never post but I've lurked here for years. hi!