Astro Bob: Crystal blue confusion
How snowflakes in a clear, blue sky created a confounding halo.
Saturday morning (Jan. 15) I stepped outside in the cold sunshine and admired the snowy fluff that had accumulated on the deck. Temperatures were in the single digits overnight and the air absolutely still, allowing multitudes of the feathery dendrites to gently lodge between each other's spines. When I positioned my eye just right, I could catch the specular (mirror-like) flash of sunlight from individual flakes. The effect was intense, with single snowflakes blazing like miniature suns from the soft heaps.
Snow, swept up by a gentle breeze, occasionally fell from the cloudless sky. Then I noticed something weird. A small, oval halo ringed the sun. I've seen halos before but not one like this. The most common type is a big circle called the 22° halo because it has a radius of 22° — about two fists. Ice crystals in high-elevation cirrostratus clouds bend or refract sunlight at a 22° angle to create this relatively common yet very beautiful sight.
There are also ice pillars , which appear near sunrise and sunset. A pillar looks like a beam or column of light standing over the low sun. It's caused by the collective glints of countless plate-shaped ice crystals hovering in the air with their flat sides parallel to the ground. The icy plates mimic tiny mirrors like the specular snowflake pictured in the photo.
But this was different. First off, it appeared in a clear, blue sky. Second, it was shaped like a hoop, not a circle. I saw it on three occasions over 15 minutes for about a minute each time. So I snapped on a telephoto lens, racked the focus in and out and discovered the source, which you've probably already guessed by now. It was the selfsame, airy-light snowflakes I'd been photographing up close but plucked and lofted by the breeze. Somehow, I don't know how, they reflected or refracted sunlight to create the odd bow, one I'd never seen before.
There's a small possibility it's the enlarged shadow of the tree projected onto airborne snow drifting in the foreground. But when I moved around, the oval remained the same shape and at the same height. Nor did freshly-blown snow from the trees in the foreground alter its appearance.
I'm curious if you've ever seen something similar and might be able to help me out. That's one reason I wanted to share this with you. The second is to tell you that you never know when nature will change your plans. I sat down more than an hour late to breakfast, hungrier and happier than ever.
"Astro" Bob King is a freelance writer for the Duluth News Tribune.