Update: Someone on Flickr blamed this effect on aircraft emissions. No, these have been around long before aircraft. They’re caused by light refracting through ice crystals, which can be near the surface or high in the upper atmosphere. They get even more elaborate in places where it’s colder near the surface and more ice crystals can be suspended in the air – diamond dust in places where people are skiing, for instance – and super-elaborate in places like the arctic and Antarctica, which can support lots of ice crystals (and the south pole doesn’t have a lot of airplanes flying over it). More info: Atmospheric Optics: Ice Halos
There haven’t exactly been a lot of airplanes flying around here over the last few weeks, either – including the day I took this photo.