The Crescent Nebula is an emission nebula in the constellation Cygnus, about 5000 light-years away from Earth. It was discovered by William Herschel in 1792. It is formed by the fast stellar wind from the Wolf-Rayet star WR 136 (HD 192163) colliding with and energizing the slower moving wind ejected by the star when it became a red giant around 250,000 to 400,000 years ago. The result of the collision is a shell and two shock waves, one moving outward and one moving inward. The inward moving shock wave heats the stellar wind to X-ray-emitting temperatures.

It is a rather faint object located about 2 degrees SW of Sadr. For most telescopes it requires a UHC or OIII filter to see. Under favorable circumstances a telescope as small as 8 cm (with filter) can see its nebulosity. Larger telescopes (20 cm or more) reveal the crescent or a Euro sign shape which makes some to call it the "Euro sign nebula".

Other IDs: LBN 203; LBN 075.51+02.29; NGC 6888; [T70] 32; Crescent Nebula; Caldwell 27; Sharpless 105; Euro Nebula; Sponge Nebula;

The Soap Bubble Nebula, also known as PN Ju 1 and PN G75.5+1.7, is a planetary nebula in the constellation Cygnus, near the Crescent Nebula (NGC 6888). It was discovered by amateur astronomer Dave Jurasevich using an Astro-Physics 160 mm refractor telescope with which he imaged the nebula on June 19, 2007 and on July 6, 2008. The nebula was later independently noted and reported to the International Astronomical Union by Keith. B. Quattrocchi and Mel Helm who imaged PN G75.5+1.7 on July 17, 2008. It is has a distance of about 4000 ly and is about 5 ly across based in its diameter.

(c) Wikipedia and other sources

https://en.wikipedia.org/wiki/Crescent_Nebula

https://en.wikipedia.org/wiki/Soap_Bubble_Nebula




A word on processing

This is my first attempt at a starless image (thank you StarNet++). My motivation to try a starless composition was because I feel the sea of stars in this area overwhelms the more subtle nebula structures. Besides the faint Soap Bubble planetary, there is ample textured hydrogen alpha throughout this area that can be more readily enhanced once the stars are removed. I tried various starless narrowband combinations of Ha, OIII, and SII, but could not decide which combination looked best, so I decided to keep bi-colour HOO, Hubble Palette SHO, and a rather psychedelic HOS.

I now routinely take RGB data for my narrowband targets to provide better star colour than that of narrowband stars. I've added a muted subset of those stars into the starless versions to produce scenes with a more traditional look.

There are still a few fires to put out in these images, including remnant Starnet++ artifacts and star core/halo problems. In the future I'll add more data and reprocess with a more experienced hand (I hope).

Imaged May to August 2020.