I've posted about sun dogs before and here's another one. It's in the top picture, to the left of the Sun. They are caused by refraction - that's a reasonable guess given the splitting into colours. It's about hexagonal ice crystals in the high cirrostratus cloud - that's cirrus done as a thin layer. It's 22 degrees from the Sun to the sun dog. Outstretched arm with thumb and little finger deployed is 25 degrees. It's about right for a rough measurement. There's supposed to be another one on the opposite side of the Sun. The cloud was a bit thicker there but I convinced myself I could see something...
