The Green Flash at Sunset

Abstract

THE explanation of the bluish (?) green flash of light sometimes seen at sunset given in your note last week (p. 495) does not seem to me to be a sufficient explanation of all the observations. If the phenomenon were due simply to refraction it would last for only a fraction of a second, and the colour would be much more blue than green. But, so far as my own observations go, the colour may last for several seconds, and is a bright peagreen, exactly similar to that shown by the sun many degrees above the horizon in South India in September 1883. To produce that green, as I have shown elsewhere, all that is required is the absorption due to a great thickness of vapour, combined with a certain amount of dust—water dust or other.