Friday 15 March 2013

Sun pillar

The Arctic skies are one of the most beautiful things about living so far north. Apart from the spectacular aurorae, there are numerous optical effects that you get from having ice crystals in the air. We have written about parhelia on several occasions now, but today's article discusses a different ice-related phenomenon... sun pillars. These are formed from reflected sunlight from flat ice crystals. The light can either be internally reflected or even reflected off the external surface.

The more general phenomena are light pillars, which can form from any light source. All that is required are the light, the ice crystals and a sufficiently dark background so that the contrast is sufficient to see the reflected light. Sun pillars are those specifically formed from reflected sunlight. They are usually easiest to see at sunset as the sun dips just under the horizon.

A faint sun pillar seen near Muonio. Photo: D. McKay-Bukowski

But as we mentioned, any illumination source could form a pillar. It is possible to see them from artificial light sources light street lamps or car headlights. And it is even possible to see them from other natural sources of light such as the moon or bright planets.

Have a nice weekend!

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