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Photo of sundogs.

Sundogs (parhelion)

Appearance

Minnesota's lack of mountains and haze means we get a front-row seat to some amazing sights in the sky. One of my favorite atmospheric apparitions is parhelion, often referred to as sundogs, two brightly colored splotches on either side of the rising or setting sun. Sometimes called mock suns, they are especially visible during winter, appearing roughly twice a week. Some people rub their eyes in bafflement at the illusion of three suns rising above the horizon.

Play of Light

Sundogs lie near the sun (para, beside, helios, the sun). They only show up around sunrise or sunset in the presence of cirrus clouds—microscopic ice crystals floating about 25,000 feet above ground. The suspended ice crystals behave like miniature 60-degree prisms, refracting light and producing mind-blowing spectacles and illusions. When the sun is close to the horizon, the flat, hexagonal ice crystals deflect sunlight at a 22-degree angle, literally shining colored spotlights on either side of the sun. On days when the sky is especially clear, an observer can see transitions of color on the mock suns, from red to blue as light moves away from the sun.

Atmospheric Conditions

The atmosphere always moistens from top to bottom; the first sign of an impending storm is a thickening veil of cirrus clouds. Add sunlight or moonlight, and a keen observer on the ground can be treated to haloes, coronas, and (if the timing is right) sundogs. The parhelic circle, a bright ring around the sun or moon, often serves as a harbinger of rain or snow.

Sundogs in History

Historically, the appearance of mock suns inspired fear and wonder. The prelude to the Battle of Mortimer's Cross in Herefordshire, England, in 1461 involved the appearance of a complete parhelion. After a British commander convinced his frightened troops that this illusion of three suns represented the Holy Trinity, his troops went on to win a decisive victory. Throughout the arc of history, the appearance of mock suns has served a variety of purposes, such as to inspire a sense of religious wonder and to celebrate one of the simplest natural wonders of the world. The next time you see three suns rising in the eastern sky during your morning commute, take a moment and reflect on how this might have given rise to fear, dread, or foreboding before science could rationalize and explain the phenomena. No cause for worry. It's just an optical illusion, and a beautiful one at that.

Paul Douglas, meteorologist

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