The Pinwheel Galaxy, M33, is a very large, beautiful, face-on spiral galaxy. It is more difficult to observe at magnification than its size and magnitude would indicate under skies that are not dark because of it's fairly low surface brightness. Still, under very dark and transparent skies, M33 can be seen with the unaided eye by keen-eyed observers. Several emission nebulae inside of M33 can be seen as pink patches in this photo and are labeled with their NGC designations in this image with object names. The largest and most prominent emission nebula is NGC 604 which is nearly 1,500 light-years in diameter. Such clouds are star factories where gas condenses under gravitational attraction and stars are born. It is one of the largest clouds of ionized hydrogen gas in the known universe. North is to the left in this image.