This lunar halo, photographed in Greenland, where the skies are wonderful. Lunar halos are rare and can be seen anywhere where there’s very thin ice crystals on the air, so they are more usual on the polar regions. Photographer Ed Stockard
Lunar halos are caused by moonlight being refracted by cirrostratus clouds. Cirrus clouds are located very high in the atmosphere, and are composed of tinny ice crystals. They bend light at a 22 degree angle, which creates a halo that is 44 degrees in diameter.