Replace the droplets of low and medium level cloud with the ice crystals of higher ones to see sub-horizon halos.
At right a subsun shines - the direct reflection of sunlight from the upper and lower faces of hexagonal plate crystals, millions of them acting as mirrors.
At left a rarer sight, a subparhelion. Rays enter a plate crystal side face, make an odd number of internal reflections between its upper and lower horizontal faces and then leave through a side face inclined 60° to the first.
For nearly every sundog there is probably, somewhere, a subparhelion. They are only distinguished by whether there are are an odd or even number of internal reflections.
Images ©Brigetta Sipocz
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