Why Do We Sometimes See a Ring Around the Moon?
A ring or circle of light around the moon is caused by the refraction, and also by reflection of moonlight from tiny ice crystals in thin, wispy clouds that are high above the Earth.
The moonlight reflects off the ice crystals and forms a big ring. Scientists call the ring a halo. It is a rare optical phenomenon, which happens during cold months. Some halos have the colors of rainbows.
High, thin clouds often move ahead of storms. So when you see a halo around the moon, you know there is a good chance that rain is on its way.
Halos sometimes appear around the sun and for exactly the same reasons. A ring around the sun usually means that a storm is coming, too.