Moon dog
![A halo around the Moon and a pair of moon dogs over the observatory at the University of Alberta in Edmonton, Canada.](/Images/godic/202501/28/Moon_dogs3706.jpg")
A moon dog, moondog, or mock moon, (scientific name paraselene, plural paraselenae, meaning "beside the 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.