The "Crescent Nebula", NGC 6888  or Sh2-105 in HOO light (cropped)
The Crescent Nebula (NGC 6888) lies in Cygnus 5,000 light-yease from Earth. It was formed by fast stellar winds from the very large hot Wolf-Rayet star WR 136 (HD 192163).  Some time between 120,000 and 240,000 years ago, WR 136 entered its red supergiant phase, at which time it ejected around five solar masses’ worth of material that is still moving away from the star.  But the solar wind that is emitted by WR 136 in its current state moves much faster than that: around 1,700km/s (1,056 miles/second).  When this wind crashes into the older, slower-moving material, it effectively bounces off it, creating an inward-moving shockwave that heats the stellar wind to X-ray emitting temperatures, giving the nebula its glow. This is a cropped HOO image photographed with a Celestron 11-inch SCT (black tube) at f/7 through 3 nm Hydrogen-alpha and Oxygen-III filters and ZWO ASI6200MM-Pro monochrome camera.  It is a joint project of James Foster and Michael Stecker.
file: NGC6888-C11HOO-a2cr3.jpg
Click here for full resolution photo

Photographic Data
telescope:
Celestron 11-inch (black tube) SCT with Starizona 0.75X reducer/flattener
Aperture: 2,794 mm (11-inches)
Focal length = 2,095 mm
Focal ratio: f/7.5

mount:
Astro-Physics 1200 GTO

guiding:
Off-axis with ZWO ASI120MM mini camera

imaging camera:
ZWO ASI6200MM-Pro monochrome camera
(cropped image)

exposure:
3 nm Hydrogen-alpha for 350 minutes and 3 nm Oxygen-III for 460 minutes.
Total exposure time: 810 minutes or 13.5 hours

photographic site:
James Foster observatory at Frazier Park California
(Bortle 4 at 5,500 ft elevstion)