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Sun Pillar, Southern California, June 14, '08 by John Garrett (site). ©John Garrett, shown with permission.

Although the sun had set, the temperature at ground level was 90F. However, at the level of cirrus and altocumulus clouds temperatures are always low enough for ice crystals to form.

Plate crystals made this pillar. High altitude sunlight reflected off their top and bottom faces.

Most halos need aerodynamically well aligned crystals but pillars are the opposite. The more the crystals wobble, the taller is the pillar.

Plates are not the only crystal to form pillars, paradoxically, horizontal column crystals can also produce them.