M 17

M17, also know as the Omega Nebula, Swan Nebula, NGC 6618, Horseshoe Nebula, Lobster Nebula, and Checkmark Nebula, is a bright emission nebula and H II region in the constellation Sagittarius, discovered in 1764. It's a prolific star-forming region ionized by a young open cluster of massive stars, resembling the Greek letter omega or a swan's neck in wide-field views, spanning about 11 arcminutes.  Apparent magnitude is 6.0. Distance from Earth is 5,500 light-years.