This is a very faint emissions nebula in the constellation of Cassiopeia. It’s so faint that it’s a really difficult object to capture unless you have a really good guiding and dark enough skies to be friendly with long exposures. I was lucky to be able to capture this on a near moonless night, so the skies were dark. I tested out using ten minute exposures on this and it worked out really well I think. This is using my short focal length telescope so it was really easy to guide and keep things solid at 10 minutes. Next time I do a capture with this, I might try for 15 minute exposures.
The nebula is mostly hydrogen gas that is being ionized to glow red by the stars forming around and behind it. The reason it doesn’t look red here is I’ve shot it in narrowband and applied a false color to it. I used what’s called the Hubble palette which assigns a color to three specific emissions spectra. Sulfur II becomes red, Hydrogen Alpha becomes green and Oxygen III becomes blue. In actuality Sulfur and Hydrogen both appear red to us, however, most of the spectrum for hydrogen is too far into the infrared for our eyes to actually see. These monochrome shots get assigned their colors and combined to form an RGB color image. The ions selected by Hubble were selected for the commonality and the colors were chosen to increase contrast. Most of your images from NASA are shot this way.
Check out more details on my personal astrophotography blog: https://www.jeromehollon.com/astro/2022-09-28-ngc-281/
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