“Green flashes are real (not illusory) phenomena seen at sunrise and sunset, when some part of the Sun suddenly changes color (at sunset, from red or orange to green or blue). The word “flash” refers to the sudden appearance and brief duration of this green color, which usually lasts only a second or two at moderate latitudes. . . .

There is a distinct, but related, phenomenon that really deserves the term “flash.” In this much rarer display, a green flash of the ordinary kind is followed (at sunset) by a brief ray or glow of green, which often appears to shoot up from the sunset point. It often accompanies, or follows, a “green dot.” These very rare displays are grouped under the term “green ray,” although the ray form is only one of several.”

—from An Introduction to Green Flashes, at http://mintaka.sdsu.edu/GF/. Photo by Pekka Parviainen.