Bright moonlight during the winter could create a rare phenomenon in the night sky. As you look up, you may notice a large halo around the moon. In the daytime this phenomenon is called a sun dog.
A moon dog occurs at night in the winter when the moon is full, or near full, casting light through high clouds. As the light passes through the cirrus or cirrostratus clouds, ice crystals create a rainbow, halo or ring around the moon. The light from the moon refract as it passes through the ice and causes a bright spot on either side of the moon or sometimes a ring. Typically the circle around the moon is colorless due to the level of light passing through the ice crystals. This event is also called a moon ring or halo.
Fun fact: the Farmer's Almanac has used this as a sign of pending rain in its publishing. Moon dogs are not as common as sun dogs.
