|Sunset Pillar ~
Ice halo imaged by Benton Henry (Photography) in South Carolina, USA.
©Benton Henry Photography 2014
|Sunlight reflects externally from the lower hexagonal faces of plates or internally from their upper faces.
The pillar is an illusion. There is no upward beam of light, only the glints towards the eye from millions of ice crystals.
|Pillar forming crystals wobble because they are large and even tending towards snowflake shapes. Those in the sketch are idealisations!|
|Sun pillars are unusual among the ice halos in that they are only seen when the ice crystals producing them are very poorly aligned.
Most pillars are produced by glints from plate habit crystals in cirrus or altostratus cloud. In very cold weather, low level diamond dust crystals can give intense pillars.
The plates wobble several degrees from horizontal. the greater the wobble the taller the pillar.