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Light pillar

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A light pillar is a visual phenomenon created by the reflection of light from ice crystals with near horizontal parallel planar surfaces. The light can come from the sun (usually at or low to the horizon) in which case the phenomenon is called a sun pillar or solar pillar. It can also come from the moon or from terrestrial sources such as streetlights.[1]

Images

Light pillars are a kind of optical phenomenon which is formed by the reflection of sunlight or moonlight by ice crystals that are present in the Earth's atmosphere. Owing to such optical phenomenon the sky sometimes seems like a natural kaleidoscope. Though light pillars seem like weather illusion , they are natural phenomena.

The light pillar looks like thin columns that that are sometimes extend vertically below or above the source of light. The Light Pillars are prominently visible when the sun is low or lies below the horizon. Normally these Light Pillars form arcs that extend from five to ten degrees just beyond the solar disc. Sometimes similar reflection of moonlight by varied forms of ice crystals may also take place thus resulting in the form of light pillars.

Light Pillars are particularly formed due to the reflection of column or flat shaped ice crystals that are present in the ice or cirrus clouds, hence the name light pillars.

  • Pillars from uncovered work lights above University of Alaska Fairbanks (J. Hall)
    Pillars from uncovered work lights above University of Alaska Fairbanks (J. Hall)
  • Sunset with prominent sun pillar near Tucson, Arizona.
    Sunset with prominent sun pillar near Tucson, Arizona.
  • Sun pillar in San Francisco, California.
    Sun pillar in San Francisco, California.
  • Sun pillar over Lake Lucerne, Wisconsin.
    Sun pillar over Lake Lucerne, Wisconsin.
  • A light pillar formed at sunset near Toronto, Ontario.
    A light pillar formed at sunset near Toronto, Ontario.

Columns of light apparently beaming directly upwards from unshielded lights are sometimes visible during very cold weather. Plate shaped ice crystals, normally only present in high clouds, float in the air close to the ground and their horizontal facets reflect light back downwards.

The pillars are not physically over the lights or anywhere else in space for that matter ~ like all halos they are purely the collected light beams from all the millions of crystals which just happen to be reflecting light towards your eyes or camera.

Artificial light pillars can be much taller than their natural counterparts because rays from the lights are not parallel and plate crystals with small tilts can still reflect them downwards. The crystals producing the pillars are roughly halfway between you and the lights.

When ice crystals float in the air around you, pillars (and other halos) can even be seen around streetlights a few metres away.

See also

References

  1. ^ "Nature's spotlights". San Francisco Chronicle. 2009-01-29.
  • Pillars. Atmospheric Optics. Explanations (10 pages) and many images.
  • Light Pillars: An Introduction to Sun Pillars and Related Phenomena. The Weather Doctor's Weather Eyes. Another nice explanation, all on one page
  • Fabulous frozen frames - Sydney Morning Herald. November 1, 2006
Wikimedia Commons has media related to Sun pillar.
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