Now that we are getting into the colder months, you can expect to see more atmospheric optical effects related to ice crystals high up in the sky, although it’s so cold up there that some of them can occur any time of year. One of the most common and spectacular of these is the halo, which forms a ring around the sun or moon. Don’t look directly at the sun, though–use something to block it so you don’t hurt your eyes!
The most common ring is at 22 degrees away from the sun. You can estimate that spacing by extending out your arm and spreading out your fingers on your hand. That distance from thumb to pinky is about 22 degrees on most people. This is formed by rays of light bending through ice crystals and getting concentrated at 22 degrees. I’ve also seen an 8 degree halo and a 45 degree halo in the past, although those are much more rare. Other atmospheric phenomena like sundogs are often associated with halos.
A ring around the sun or moon is a favorite folk sign forecasting rain or snow within 48 hours. This is because the presence of moisture high up in the atmosphere is one of the first signs of an approaching warm front, which often brings rain to the area.
You can read about halos and other atmospheric phenomena at EarthSky here.
