You don't need rain falling over a warm tropical island to see rainbows; freezing air works too. It is now -36 F at the Fairbanks airport and just below -20 F up in the hills. At these temperatures, all moisture in the air freezes into tiny crystals, referred to as diamond dust, that gently rain down and powder coat all surfaces with frost. This diamond dust acts like millions of randomly distributed prisms in the air, refracting the colors of the spectrum into a 22° halo around the sun. As the tiny ice crystals fall from the sky they tend to orient themselves vertically, sort of like having a bunch of falling hexagonal disks all in vertical alignment. These little ice disks flutter as they fall, and due to their orientation instead of refract, they reflect the sun's light, forming a second phenomenon called the parhelic circle; more like like an arc parallel to the horizon with the sun as the midpoint. Are you with me? Where the parhelic circle intersects the 22° halo, the refracted light from the sun is exaggerated by the combined reflection of the ice crystals, forming what are called "sun dogs". Winter's version of a rainbow. This is the left-hand sun dog pictured here, red is always facing the sun.
If that still doesn't make sense check out this link: http://spaceweather.com/images2015/25jan15/halos_labelled.jpg?PHPSESSID=bdipp77uf3trf4qfchnsf73un2
Canon EOS 60D, Canon EF 70-200mm f/4L USM +1.4x, ISO-200 f/20 @ 1/160 sec
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