The Beauty In The Skies Sun Dogs, Halos, and Sun Columns

Those who spend time in the skies are privileged to see some of the unique and fleeting atmospheric events that occur throughout the seasons. One of these unusual and beautiful atmospheric events is what we often refer to as a “Sundog,” or Sun dog. The actual name is Parhelia. Some people may also refer to them as mock suns. Sundogs are closely associated with the 22-degree halo.

They can most easily be seen when the sun is low in the sky, though they can occur when the sun is also very high in the sky. The most immediate difference between those conditions is that when the sun is low, the Sundogs will be found at the same height and will appear relatively close within your field of vision. The higher the sun gets, the further apart the Sundogs appear to be. Their brightness varies with the conditions. Some may be brilliant and colorful, while others may be somewhat muted in intensity and color.

Sundogs are formed in the upper atmosphere when horizontal plate ice crystals form. When these crystals fall relatively undisturbed by wind, they automatically orient themselves horizontally. Thus, when the sunlight passes through crystal side faces at 60 degrees to each other, the light is bent up to 50 degrees. But the light rays nearest to the minimum deviation of 22 degrees are the most numerous and form the bright inner edges of the sundog. When the crystals refract the incoming light by different amounts, the colors are created.

The 22-degree halo mentioned in the first paragraph is created when sunlight encounters columnar ice crystals. As the light enters the crystal, it is refracted, and is refracted once again when it exits the crystal, thus creating the observed halo. The amount of refraction depends on the actual diameter of the crystals. Randomly oriented hexagonal crystals create the observed halo, while horizontally oriented hexagonal crystals with their flat faces horizontally aligned, create the observed Sundogs.

Sun columns or pillars are created when light from the sun shines up (from the low sun angle as seen by the observer), through relatively undisturbed ice crystals. They are falling in a fairly straight line from the base of a thin cloud very near or at the top of the column of light. Because of the angle of the crystals as they fall, the light shining into and coming out of them is equally refracted, thus retaining the color of the incident sunlight.

The millions of slowly falling crystals appear to form a visually “solid” column of light. This gives the observer the impression that the light is being beamed up from the sun in a singular column. “Lower” pillars are formed when sunlight is reflected upwards from the topmost crystal face. “Upper” pillars are created when light rays are reflected downward from the lowest faces of the crystals.

These are just a very few examples of the beauty in the skies that can be seen with amazing clarity from the air. While the events mentioned here can also be seen from the ground, nothing compares to what can be seen when in flight. It makes the pleasure of flying even greater.

This entry was posted in Columns, Columns, February/March 2013, MN Aeronautics Bulletin and tagged , , . Bookmark the permalink.

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