Moon Dogs is a collection of science fiction short stories and essays by Michael Swanwick. It was published in 2000 to commemorate his appearance as Guest of Honor at Boskone 37. It includes collaborations with Gardner Dozois and Jack Dann.
Moon Dogs are a celestial phemenon, where a pair of images of the moon, usually a full moon, appear horizontally beside the rising or setting moon, at a distance of 22 degrees, caused by refraction of the moon's image by ice crystals. When the moon is higher in the sky, this refraction results in a "Ring Around the Moon" See Wikipedia article on Sun Dogs. Moon Dogs are very much rarer than Sun Dogs.