"Fieldnotes," December 8th & 9th, 2013: "Rainbows," by Caroline Kurtz.
http://www.montananaturalist.org/
"The interplay of sunlight and water droplets or ice crystals in the air can produce such ethereal effects as halos and glories, sundogs, circumzenithal arcs, coronas and iridescent clouds. Sun and moon halos are the result of light refracted, or bent, by tiny six-sided ice crystals tumbling around in the wispy (high altitude) cirrus clouds. These crystals act as prisms, causing each wavelength of light to deviate somewhat from its original path and spread white light into the different colors of the spectrum."