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Sunday, April 20, 2014

Strange columns of light in sky caused by ice crystals

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These strange columns of light shinning from the sky in Latvia were caused by the natural phenomena of ice crystals reflecting bright light on to the ground - and not by UFOs.

Strange columns of light in sky caused by ice crystals
Light pillars only appear in winter when city lights shine upward into the icy airPhoto: National

The images were taken by designer Aigar Truhins with a standard digital camera in Sigulda, Latvia, last month.

The air was quite cold and indeed filled with small ice crystals, just the type known to create light pillars and moon halos.

Light pillars only appear in winter when city lights shine upward into the icy air. Reflections from plate shaped crystals spread the light into a vertical column.

They only happen when the crystals are oriented mostly horizontally, and that happens when they are falling in calm air, like a leaf falling.

The reason why the dramatic pillars fan out at the top is currently unknown but could be a natural behaviour of the light itself. Even laser lights spread out over long distances.

In this case, there could be some wind higher up and it is calmer lower down, and the 'fan out' of the light pillars happens near the boundary between calm and stirred up air.

The crystals near the boundary would tend to be close to horizontal but as you get higher into the wind, their orientations are more dispersed, so the reflections would be more spread out form the vertical line.

The differences in colour responds to the source of the light. Mercury vapour lights are somewhat blueish or red, while high pressure sodium lights appear reddish or yellowish.

Copyright: Telegraph

 
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