Anza-Borrego Desert State Park - Kevin Key Photography - San Diego, California
Moon Halo, Mountains, and Smoketree in the Anza-Borrego Desert

Moon Halo, Mountains, and Smoketree in the Anza-Borrego Desert

Shot near Dos Cabezas Siding in Anza-Borrego Desert State Park.

A 22° halo is a halo, one type of optical phenomenon, forming a circle 22° around the sun, or occasionally the moon. It forms as sunlight is refracted in hexagonal ice crystals suspended in the atmosphere. As the light beam passes through two sides of the prism forming a 60° angle, the angle of minimum deviation is almost 22° (namely, 21.84° on average; 21.54° for red and 22.37° for blue). This wavelength-dependent variation in refraction causes the inner edge of the circle to be reddish while the outer edge is bluish. A 22° halo may be visible on as many as 100 days per year.

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