the bending of light

The bending of light as it passes from one medium to another is called refraction.

The angle and wavelength at which the light enters a substance and the density of that substance determine how much the light is refracted. The refraction of light by atmospheric particles can result in a number of beautiful optical effects like halos, which are produced when sunlight (or moonlight) is refracted by the pencil-shaped ice crystals of cirrostratus clouds.

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Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.