A vocabulary of landscape — a landscape of words
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moondog
A moondog is a bright patch beside the moon, 22 degrees to one side, produced the same way a sundog is: moonlight refracting through flat ice crystals drifting horizontally in high cloud. They come in pairs.
Etymology
The English name is built directly on sundog. The formal term is paraselene, Greek for beside the moon, exactly paralleling parhelion for the solar version.
Notes
Everything the sun does in ice crystals the moon does too, and there is a full parallel set: lunar halos, lunar pillars, lunar arcs, and moondogs. They are all rarer only because there is less light, not because the physics is any different. A halo around the moon is the one member of the family almost everybody has seen without knowing what it was.