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A rising sun and two sundogs were caught on February 7, 2003, near Park City, Utah. The sundogs appear in front of the scenery because they are generated by tiny "diamond dust" ice crystals in the nearby air.
Tiny crystals, huge delights
Ice crystals high in the sky or down to earth give rise to gorgeous patterns of light
By Deane Morrison
December 28, 2005
It was as if a forest of light had sprung up, its innumerable thin shoots of radiance reaching up into the dark sky. Such was the situation in many parts of Minnesota on the evening of December 3, when eerily beautiful pillars of light stood everywhere, like vertical streams of aurora borealis frozen in place. But these columns of light were no aurora borealis; rather, they were a rare atmospheric phenomenon called ice pillars, the result of reflections off ice crystals near the ground. They are cousins to such striking displays as sun pillars, sundogs, and halos, all caused by the interactions of light and microscopic ice crystals in the air--with an occasional assist from that master generator of illusions, the human brain. Ice crystals in the atmosphere cause these various displays by either reflecting or refracting light from the sun, moon, or artificial sources on the ground. Let's look first at sun pillars and ice pillars, which result from reflection. Ice crystals are essentially six-sided plates that act just like mirrors. Suppose you're looking into a big flat wall mirror at the image of a light bulb off to your right. If you could see only the bulb's reflection--not the room around you or the edges of the mirror--you would think the bulb was to your right but in front of you.
Perhaps the most spectacular manifestation of refraction is sundogs, or parhelia, which are bright spots on either side of the sun.What happens is that light from the bulb hits the mirror at a certain angle and bounces off at the same angle, hitting your eyes. You see the image coming to you in a straight line from the mirror. Your brain extends that line and "tells" you that the bulb is behind the mirror, as far from its surface as the real bulb actually is. If you rotated the room so that the mirror was on the ceiling, the bulb would appear to be the same distance above the mirror surface as it really is below it. That's what happens when the air is full of tiny ice crystals oriented with their flat surfaces horizontal. Like so many mirrors, the crystals reflect light to your eyes and cause you to project an image above the source of the light. In the case of the ice pillars on December 3, the light sources were streetlights, store lights, and so on. The mirrors were ice crystals in a column of air midway between each light source and each observer. Image(55804)