|Light Pillars, Calgary, Alberta
Imaged by Larry McNish (Calgary Center RASC).
"Calgary has been experiencing one of the coldest run of February and March temperatures in recent memory. After midnight on March 5 at -20 C, with a light shower of fine falling ice crystals (needle-like) in the air and almost no wind, we spotted these light pillars on just about every sodium and mercury vapour light in the area.
The top is a tripod shot, 1.3 second, f/5.6, ISO 800, 42mm lens. Sodium streetlights on Sunvalley Blvd. [Canon EOS Digital Rebel XSi]."
©Larry McNish, shown with permission
|Crystals roughly half way to the light reflect its rays towards the eye.
The millions of glints appear to form a vertical pillar over the light.
This is purely an illusion, there is no pillar located anywhere in space and no upward beam of light.
In this sense all halos are illusions!
|Light pillars are usually produced by hexagonal plate-shaped ice crystals in low cloud or in ice fogs at ground level.
The crystals drift very slowly downwards (only a few mm/s) relative to the direction of local air currents. They are not necessarily falling towards the ground.
The drift motion sets up an aerodynamic drag that aligns them with their large hexagonal faces nearly horizontal.
The large faces act as mirrors and glint light from lamps on the ground back downwards.
Sun pillars need crystals that wobble from the horizontal orientation. They can also form light pillars at night but tilted crystals are not essential.
Other crystals sometimes form pillars - sometimes with odd effects.
Light pillars in ice fogs are attractive but the lighting that produces them is not. Unshielded upward shining lighting is bad design, wastes energy, hinders vision by its glare and denies billions the beauty of the stars. IDA
|"0.5 second, hand-held shot, f/5.6, ISO 800, 24mm lens, A small college campus near the restaurant we just left has 3 different coloured pillars. In the centre is an old wooden tower - all that remains of a large wooden building that burned down several years ago. Steam is rising from a church building on the right."|