A sun pillar is a golden or reddish column of light extending vertically from the sun, especially visible at sunrise or sunset when the sun is low. It is produced by reflection off the horizontal faces of flat plate-like ice crystals falling slowly with near-horizontal orientation.
Variants
Moon pillars (with full moon) and artificial light pillars from street lamps on very cold nights with surface ice crystals can also form. They should not be confused with halos, which are caused by refraction. Pillars are more common at high latitudes with stable Arctic air.