It is a kind of Halos. The reason for formation is that in the hexagonal plate-shaped ice crystals contained in the high clouds. Due to the plate-shaped of the ice crystals, the sun's rays on the horizontal plane are incident from the ice crystal at an angle of 60°, producing a dispersive light with a refraction angle of about 22°, so that the observer can see the phenomenon of a bright spot on the both sides of the sun at a viewing angle of about 22°. , And the sundog can actually be regarded as part of the 22° halo.