The Rosette Nebula is a large HII region in the winter constellation Monoceros. Nicknamed the rosette for obvious reasons (and also the skull nebula), Caldwell 49 is about 5,000 light years from Earth, sort of near the star Betelgeuse. The Rosette is also very close to a really large supernova remanant named the Monoceros Loop (not to be confused with Barnard’s Loop in nearby Orion), sitting at the edge of it like a diamond in a ring.
This is one of my favorite nebulae in the entire sky, and I make a point of shooting it every year. This year’s photo was first light for my new camera- the ZWO ASI6200-MM-Pro! This is my first monochrome, dedicated astronomy camera, and it’s absolutely amazing. To take this obviously not monochrome photo, I took photos through a hydrogen filter and an oxygen filter, which isolate the 656nm and 500nm wavelengths respectively, which correspond to light emitted by hydrogen and oxygen. This lets me see just where the oxygen is in the nebula, and where the hydrogen is. In the rosette, the oxygen is very much overpowered by the hydrogen emissions, but the whiter core of the nebula is full of oxygen. I then set the hydrogen photo to be red (which it is), and oxygen to be green and blue (oxygen’s a teal blue). The result is this HOO photo, which is very close to true color but more detailed.