Sundogs in Antarctica
The parhelia or "sun dogs" are more readily visible in the cold of the antarctic and artic regions.
Photos by Dr. Richard Sadleir. Used by permission. All rights reserved.
"I also noticed something I had not seen in previous sun haloes, perhaps because this was in perfect conditions. The light ring of the halo was very intense on the sun side of the halo and then faded outwards. "
"After the whole phenomena faded, the cloud of ice crystals actually fell around us for a short time. They were elongated crystals about 8 to 12 mm long. I remember them as falling vertically (the air was absolutely still)."
The coloration of the sundogs arises from dispersion in the ice crystals, which act as 60° prisms to separate the colors of sunlight. The prism calculation using n=1.306 for red and n=1.317 for blue gives angles of 21.54° and 22.37° for red and blue respectively. The inner edge of the halo is sharp and appears reddened - the angle of minimum deviation for red is less and you see it from crystals closer to the Sun or Moon direction. The out edge of the halo is blue in appearance but less saturated because other wavelengths can refract at that angle.
Atmospheric optics concepts