Atmospheric Optical Phenomena

One of the most dramatic examples of sunlight refraction is the green flash. That term refers to the fact that in the moment following sunset or sunrise, a flash of green light lasting no more than a second can sometimes be seen on the horizon on the upper part of the sun. The green light is the very last remnant of sunlight refracted by Earth's atmosphere, still observable after all red, orange, and yellow rays have disappeared. The green light remains at this moment because the light rays of shorter wavelength—blue and violet—are scattered by the atmosphere. Sundogs at sunset on the frozen sea at Cape Churchill, Hudson Bay. © Dan Guravich 1987, National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission.

The green flash is rarely seen, but when it is, it makes a remarkable impression on the observer.