|Refractions & Reflections
Sundogs pictured near Dunsmuir, California by Jim Young (Photo Gallery). ©James W Young, shown with permission
Contrary to popular descriptions, reflections are essential in the formation of most sundogs.
Horizontal plate crystals form them. Light enters a side face and leaves through another on the other side of the crystal inclined 60° to the first. The two refractions disperse the light and produce the colours.
However, to be channeled successfully from one side of the crystal to the other the rays must be internally reflected up and down between the large hexagonal top and bottom faces.
The higher the sun the more internal reflections are needed. Only near sunset and sunrise can sundogs form without reflections.