Halos

Partial Solar Halo

The phenomenon of a circle of light sometimes spotted around the sun or moon are known as halos. These are caused by the refraction and reflection of light on ice crystals in the upper atmosphere. High, thin cirrus clouds are made of millions of ice crystals in the upper troposphere, part of the atmosphere almost always below freezing, and are a reason these halos. While a halo can therefore be seen year-round, the descent of the northern jet stream southward from fall to spring brings even more of these ice crystals into the air.