Holiday Pillar

December 31, 2003


Provided and copyright by: Jennifer Oehler
Summary authors & editors: Jennifer Oehler; Jim Foster

This curious beam of light was captured above Calgary, Alberta and is known as a pillar. Unlike the beam of light shown on the Earth Science Picture of the Day for December 29, the ray above isn't an artifact of the camera. Rather, it's a true optical phenomenon. Pillars are usually associated with reflected sunlight, however, the above photo was taken at night. An ice fog enshrouded the landscape (the air temperature was -25 C or -13 F), and all of the street lights appeared to be shining straight up. As with all pillars, oriented hexagonal plate crystals (composing the ice fog) produced the vertical beams, but here, the light source was the street lamps rather than the Sun. Light is refracted through the underside of the plate crystal and then reflected off of the upperside before exiting the way it entered, through the underside. The brightest beams of light typically result when the crystals are all nearly perfectly aligned and are of similar size.


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