Sun Pillars appear as a shaft of light extending vertically above the sun, most often at sunrise or sundown. Look for sun pillars when the sun is low on the horizon, and cirrus clouds are present. Our Office Staff Want a tour? Looking for a speaker? Please Contact Us. Please try another search. Multiple locations were found. Please select one of the following:. Location Help. News Headlines. Customize Your Weather. Go here to link your subscription. Need help?
Visit our Help Center. Go here to connect your wallet. Only ice crystals that are flat and hexagonal—known as plates—can create halos. If the majority of these plate-shaped ice crystals are positioned with their flat sides horizontal to the ground, you will see a sundog. If the crystals are positioned at a mix of angles, your eyes will see a circular halo without the distinct "dogs. Sundogs can and do occur worldwide and during all seasons, but they are most common during winter months when ice crystals are more abundant.
All that's needed for a sundog to form are either cirrus clouds or cirrostratus clouds ; only these clouds are cold enough to be made of the necessary plate-shaped ice crystals.
The size of the sundog will be determined by the size of the crystals. The sundog occurs when sunlight is refracted off of these plate crystals per the following process:.
Does something about this process sound vaguely familiar? If so, it's because another well-known optical weather phenomenon involves the refraction of light: the rainbow! Sundogs may look like bite-sized rainbows, but inspect one closer and you'll notice that its color scheme is actually reversed.
Primary rainbows are red on the outside and violet on the inside, while sundogs are red on the side nearest the sun, with colors grading through orange to blue as you travel away from it. In a double rainbow, the colors of the secondary bow are arranged in this same way.
Sundogs are like secondary rainbows in another way too: Their colors are fainter than those of a primary bow. There are also moon dogs that appear alongside the moon and are formed by lunar light passing through ice crystals. Moon dogs, or paraselenae, are not observed as often as sundogs because they are visible when the moon is bright and because they appear during the night. Sundogs are formed from hexagonal ice crystals in high and cold cirrus clouds or, during very cold weather, by ice crystals drifting in the air at low levels.
These crystals act as prisms, bending the light rays passing through them. As the crystals sink through the air they become vertically aligned, refracting the sunlight horizontally so that sundogs are observed. Sundogs frequently display a reddish tint on the side facing the sun and may sport bluish-white tails that stretch horizontally away from it. The sundog's tail is formed by light passing through the crystal at angles other than the optimal deviation angle.
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