Seamen traveling at sea, particularly in the tropics, have long noted the phenomena of a green flash as the upper limb of the sun passes beneath the horizon on a clear night. Because it is rare, particularly in higher latitudes, many have thought it a sailors dream. It isn't!!!
Dutton's Navigation and Piloting explains it this way. It is caused by refraction of light waves from the sun, as they pass through the earth's atmosphere. These light waves are not refracted or bent equally, the longer waves of red being the least refracted, the shorter waves being more refracted. The longer red waves are cut off by the horizon before the shorter, more highly refracted waves. The result is that the last light to be seen from the sun appears green, lasting for one half to one second.
No, its not caused by little green men.
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