AstronomyPicture of the Day—20181222

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2018 December 22

RedNebula, Green Comet, Blue Stars

ImageCredit & Copyright: Tom Masterson (Grand Mesa Observatory)

Explanation:This festively colored skyscape was captured in the early morning hours ofDecember 17, following Comet Wirtanen's closest approach to planet Earth. Thecomet was just visible to the eye. The lovely green color of its fluorescingcometary atmosphere or coma is brought out here only by adding digitalexposures registered on the comet's position below the Pleiades star cluster.The exposures also bring out blue starlight reflected by the dust cloudssurrounding the young Pleiades stars. Gaze (toward the left) across dusty darknebulae along the edge of the Perseus molecular cloud and you'll travel toemission nebula NGC 1499, also known as the California nebula. Too faint forthe eye, the cosmic cloud's pronounced reddish glow is from electronsrecombining with ionized hydrogen atoms. Around December 23rd, Comet Wirtanenshould be easy to find with binoculars when it sweeps close to bright starCapella in the northern winter constellation Auriga, the Charioteer.