The Crescent Nebula NGC 6888 in the Constellation Cygnus.

 

The Crescent Nebula NGC 6888 captured from the Jodrell Plank Observatory using a Seestar S30 in EQ mode and it's integral light pollution filter. - 50 x1 minute exposures. Image capture and processing Credit: Pip Stakkert.

" Lots going on in this image as the Crescent Nebula sits in the plane of the Summer Milky Way's Disc. Huge amounts of ionized gas creating the red clouds and tendrils punctuated by the dark black clouds of dust. In this photograph there are many hot blue young and enormous stars, which are collectively responsible for ionizing the widespread clouds of Hydrogen gas. The Crescent Nebula has a different  and more interesting source of ionization." - Kurt Thrust current Director of the Jodrell Plank Observatory.

"The Crescent Nebula (NGC 6888) is an emission nebula located approximately 5,000 light-years away in the constellation Cygnus. It is about 25 light years across!

The structure is not ionized by a standard B-type main-sequence star, but rather by WR 136 (HD 192163)—a highly evolved, massive Wolf-Rayet star located near the centre of the nebula. 

Wolf–Rayet (WR) stars represent an advanced, highly unstable evolutionary phase of initial massive stars (typically exceeding 20–25 solar masses). Having exhausted core hydrogen fusion, these objects are defined by extraordinarily high surface temperatures, extreme bolometric luminosities, and hyper-velocity stellar winds driven by radiation pressure.

The Wolf-Rayet Star, WR 136
ionizing the Hydrogen Gas
and making the Crescent Nebula glow.  

Formation Mechanism & Dynamics

Mass-Ejection Phase: Around 100,000 to 200,000 years ago, as the massive progenitor star evolved off the main sequence into a Red Supergiant (RSG) phase, it shed its outer envelope in a slow, dense stellar wind expanding at roughly 80 km/s.Shock Shell Formation: As the core collapsed into the Wolf-Rayet phase (spectral type WN6), the star's extreme surface temperature (approximately 70,000 K) drove an exceptionally fast stellar wind reaching velocities up to 1,700\ km/s. This high-speed wind caught up to and collided with the slower RSG shell, creating a swept-up shock boundary with complex filamentary geometry.

Photoionization & Emission: Intense ultraviolet radiation emitted by WR 136 photo-ionizes the surrounding gas. In this narrowband image, the deep red regions showcase recombining hydrogen (H alpha emission at 656.3 nm), detailing the intricate, shell-like shock fronts embedded within the dense interstellar medium of the Cygnus region". - Gary Gemini Comms Manager at the JPO