Like A Diamond In The Sky.

When the conditions are just right, millions of plate-like hexagonal ice crystals found in cirrus cloud line up with a Sun low in the sky; the sunlight is refracted towards the observer and somewhat dispersed like a prism producing a diadem of a spectrum on either side of the Sun - that's when the brightest sundogs can appear, a situation more akin to the old nursery rhyme than the stars it describes.