The bright star in the top-left is called Gamma Cassiopeiae, and is around 550 light-years from Earth. It’s almost 20 times more massive and 65,000 times brighter than the Sun, and rotates so fast — 1.6 million kilometres per hour — that it blasts out intense ultraviolet radiation, eroding the nearby Ghost Nebula and causing hydrogen gas to glow red. Other parts of the nebula reflect Gamma Cassiopeiae’s strong blue light.

Being a reflection and emission nebula meant that I decided to collect data using my Optolong L-Quad Enhance (for RGB) and Optolong L-Ultimate (for Ha and OIII). I used this approach recently for the Flaming Star Nebula and it worked well. For more info, check out my guide to choosing filters for your OSC camera. Use the slider below to compare quick edits of the RGB and Ha/OIII data. You can see how various elements from both make it into the final image. I think it’s interesting from a scientific viewpoint too, as when looking at the two images side-by-side you can compare the emission (red) and reflection (blue) elements really well: