A moon dog, moondog, or mock moon, is a relatively rare bright circular spot on a lunar halo caused by the refraction of moonlight by hexagonal-plate-shaped ice crystals in cirrus or cirrostratus clouds. Moon dogs appear as part of the 22° halo, roughly 10 Moon diameters outside the Moon.

What are Sundogs and moondogs?

Often, however, they may seem to appear without the halo. By day, with the Sun, one of these phenomena is called a parhelion, or sun dog. By night, it is called a paraselene, or Moon dog. Look for a Moon dog when you see high, thin, cirrus clouds near the Moon.

What does a moondog look like?

What happens is that the ice crystals or clouds refract the moonlight, creating blobs or arcs of light to the left and right of the Moon, or sometimes just on one side. ... Moondogs can appear colorful like a Sundog or 'shine' with a light similar to the Moon.