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The pillars arise for the very same reasons as those produced by column
crystals. The combination of the two possible crystal rotations
causes the prism end faces to have a greater probability of being nearly
horizontal than being inclined at other angles.
|A sun pillar, sundogs and what at first sight looks like a 22° halo all produced by plate crystals with rare Lowitz orientations. The pillar and sundogs appear because the prism end faces of Lowitz oriented crystals are more likely to be nearly horizontal than be otherwise tilted. Lowitz pillars are tall even when the sun is moderately high. The almost circular halo is a combination of the upper and lower circular Lowitz arcs. HaloSim simulation. for a solar elevation of 1º.|