Sundog imaged by Geir ye (site) at Ørsta, Norway.    ©Geir ye, shown with permission
Atmospheric
Optics

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Sundogs are created by sunlight refracted through hexagonal plate shaped ice crystals.    Aerodynamic drag orients them quite precisely with their large hexagonal facets nearly horizontal as they drift slowly downwards relative to local air currents

Sundog rays enter a vertical side face and leave through another inclined 60° to the first.

Most sundog rays are also internally reflected from the upper and lower faces. Zero or an even number of reflections create the dog.

Geir's beautiful display also has a trace of a parhelic circle and perhaps a very faint 22 degree halo fragment.