Comet 17-P-Holmes and its - now - Green Coma

Caption NASA:"This gorgeous skyscape spans some 10° across the Constellation of Perseus, about the size of a generous binocular field of view.
The deep exposure includes bright stars, emission nebulae, star clusters, and, of course, the famous Comet Holmes.
The brightest star in view, Alpha Persei, is itself surrounded by a loose cluster of stars - the Alpha Per Moving Cluster - at a distance of about 600 LY.
But, at a distance of a mere 14 Light-Minutes (LM), bright Comet 17-P-Holmes still dominates the scene with its fluorescing greenish coma and foreshortened blue tail".