An Equinox Sundog

Disclaimer: The term sundog is often used incorrectly to refer to a group of optical effects caused by sunlight refracting through ice particles in the air. But, in keeping with my aversion toward conformity, I’m going to call the damn thing a sundog anyway. The collective of optics is correctly referred to as a halo, which may or may not contain a myriad of rainbowy arcs and shiny spots—only one of which is called a sundog (or technically, a parhelion).

At the end of my 2012-2013 winter at Summit Station I saw the beginnings of a sundog. It was amazing. Though I had lost my mind by that point (see Basically Bipolar, the Book), the sundog made me want to stick around, sort of.

On either side of the sun was the start of an intense rainbow: two crimson-through-indigo pillars with the solar blaze between them. The outer edges of the pillars, where there should have been violet, instead projected spotlight beams of white light along the horizon, like the sun’s high beams.


That sundog tease was one of the reasons I returned to Summit. I figured, with the sun back up, but temperatures still frigid, springtime must be prime season for sundogs. Today, on the spring equinox, my gambit paid off—big time.


The immensity of this optic effect was breathtaking. What I didn’t realize about sundogs is that they can take up the entire sky. There are layers and layers of known optical arcs and swoops that may form throughout the firmament. Most of them are rare. The smiling rainbow at the top of the above picture is called a circumzenithal arc. It is actually almost directly overhead. According to a ten year study by zhe Germans, this optic occurs in 13 of 100 sundogs. Parhelia (the actual sundogs) are the bright spots to the left and right of the sun—its high beams. They are more common, occurring in 73 of 100 sundogs. A parhelic circle occurs in only 4 of 100 sundogs. I couldn’t possibly capture the parhelic circle in the picture because it wraps around the entire horizon. Seeing that was truly a WTF moment.

If you’d like to learn more, this is a great website:
https://www.atoptics.co.uk/halosim.htm

Happy equinox!

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