This afternoon, I had the good fortune to witness one of the most vivid sun dogs I have ever seen. Sun dogs are an optical phenomenon that occurs fairly often in Fairbanks, though I don’t recall ever before seeing them so early in the winter season. Unfortunately, I had only my phone camera available and the full range of brightness in the scene was beyond its capacity to record. To the naked eye, the sun dog had a sharply-defined bright nucleus and varied in color from red to yellow. Those details were, sadly, not realized in the image.
When conditions are appropriate, water in the atmosphere freezes in the shape of hexagonal plates. Sometimes, the air is stable enough that these plates will drift gently downwards under the force of gravity. As they settle, the plates tend to organize themselves with their flat faces parallel to the ground. In this orientation, sunlight can enter a plate through one of the side facets and exit through another. The result is that an image of the Sun appears at an angle of 22 or 44 degrees to either side of the actual Sun.
The sun dog I saw today was 22 degrees to the left of the Sun. There were two indications that the ice crystals had not formed and arranged themselves optimally. First, there was no sun dog to the right of the Sun. Second, there was a short length of arc extending upwards and downwards from the sun dog.
If the ice crystal plates are not uniformly arranged, sunlight can reflect or refract at a variety of angles. One result is an arc or halo of light surrounding the Sun. Two of the most common types of haloes have perimeters at 22 or 44 degrees from the Sun. There are a great many more varieties of arcs and haloes possible.
When an ice halo forms in the sky, the area inside the arc is darker than outside the arc. In the second image you can better see the difference in the sky. The rays of sunlight cannot refract through the ice plates at any angle smaller than 22 degrees. Thus the inner area is deprived of the refracted light that brightens the outer area.
The last few days have offered us excellent views of the aurora and an early start on sun dogs. Living in Alaska is not for everyone, but there are some wonderful compensations for those of us who have made the choice.
Spectacular! The image which appears in this “comment” page (versus the initial one with the script) shows exactly what you so excellently describe.
Yes, you have a marvelous trade-off for putting up with the extreme temperatures you endure.