There are many interesting things to look at (or for) in the daytime sky besides the sun. There are various halos, arcs, sundogs, pillars, and other light phenomena that are more common than you might think. Most of these are caused by sunlight (or, at night, moonlight) reflecting or refracting through ice crystals in high cirrus or cirrostratus cloud layers.
I have tried to make a habit of glancing at the sky whenever I am outdoors, especially when there are high, thin clouds of the cirrus type in front of the sun. A few days ago at work, I was crossing the street from our warehouse to our office building in the late afternoon when I noticed these types of clouds. I immediately looked for sundogs (bright rainbow patches of light at least 22 degrees to either side of the sun and parallel to the horizon) but I didn’t see any. So, I glanced upward to a spot halfway from the sun to the zenith. I had looked to this particular spot dozens of times in the past seeking a phenomenon called the circumzenithal arc but had never seen it. This time, however, my persistence was rewarded with a small but distinct upside down rainbow not more than two or three degrees wide. I stood there for a minute, transfixed by this ethereal vision, until I thought, “Camera! I need to take a picture.” I hurried to my car, got the camera, and snapped this shot.
Circumzenithal Arc / Copyright 2012 Robert D. Vickers, Jr.
It’s dim, but look near the center where the jet vapor crosses. The clouds scudded across the sky and the arc didn’t last long. Like the smile of the Cheshire cat, it faded in and out and finally disappeared altogether.
