The Crescent Nebula is an emission nebula in Cygnus a couple of degrees from the star Sadr, not far from the region in this image. According to Wikipedia, its shape is caused by a shockwave from Wolf-Rayet star WR 135. The fast stellar wind is catching up to a slower, older stellar wind that was ejected about 25,000 years ago. The interaction causes the shape.
Stars were my major problem when processing this image. The background was filled with thousands of tiny, faint stars that caused the image to look like it was printed on a fuzzy sweater. This is a second processing attempt that I think succeeds better than the first image. While there are a lot of stars they don’t overwhelm the image quite as much and there is a fair amount of detail in the crescent.
This was challenging to process and brought me back to earth after the relative ease for M16. I think it was worth persevering though!
In early October, 2019, I reprocessed this using the same techniques I used in the eastern veil. This doesn’t try to extract every last bit of nebulosity but strives for clarity in terms of star size and managing noise.
You can find the image at astrobin.