I have been seeing a rainbow of colors in the sky lately, but they haven’t been the result of a passing rain shower. Late in the afternoon, when the sun is low in the sky and cirrus clouds are present, one can often make out this colorful display right through the cirrus clouds themselves. The phenomenon is called a “sun dog,” and occurs when sunlight is refracted, or bent, by ice crystals. Cirrus clouds are those clouds that are often wisplike in appearance, and reside high in the atmosphere beginning around 16,000 feet. They are made up entirely of ice crystals. When light passes through these ice crystals, many different optical effects can occur, depending on the angle of the sun, and the shape and orientation of the ice crystals.