The moon dog, moondog, or mock moon (scientific name paraselene, meaning “beside the moon”) is a comparatively rare circular point on a lunar halo caused, in cirrus or cirrhostratus clouds, by refraction of lunar luminous ice by the moonlight of hexagonal ice crystals. As part of the 22° halo, moon dogs appear, approximately 10 Moon beyond the Moon diameters. It is precisely identical with sun dogs but is rarer since the Moon needs to be luminous for moon dogs, about a quarter of the moon or longer. Moon dogs show the unassisted human eye little colour, as their light is not as bright as it can activate cells in the cones.
