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The “Green Ray” or “Green Flash” (Rayon Vert) at Rising and Setting of the Sun


WHEN the sun sets behind a distant and clear horizon, its last rays disappear with an emerald green flash. The coloration is due to the refraction of light in our atmosphere by which the sun's image is raised through about half a degree, the elevation increasing from the red to the violet end of the spectrum. As the violet and—to some extent—the blue rays are absorbed by the layer of air through which the light has to pass, it is the bluish-green part of the spectrum that is dominant at the ultimate moment of sunset. This seems clear enough and even obvious. But there are always certain minds that distrust the obvious—not always to the disadvantage of science—and others which rebel against a commonplace explanation of a striking effect. Imagination is always ready to supply more or less fanciful alternatives leading to controversies and correspondence in scientific journals.

The "Green Ray" or "Green Flash" (Rayon Vert) at Rising and Setting of the Sun.

By Prof. Dr. M. E. Mulder. Pp. 141. (London: T. Fisher Unwin, Ltd., 1922.) 6s. net.

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