NGC6888 Crescent Nebula

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2014/07/17 - Fourth light of our remote setup. This time a nice narrowband object, The Crescent Nebula. This image is a combination of 6 channels; Hydrogen-alpha, Oxygen-III, Sulfur-II and RGB for correct star color. We spent 35 hours on this object, that's our record for now. Seeing fluctuated during the 8 days we images this object, it was between 2" and 5".

The Crescent Nebula is an emission nebula in the constellation Cygnus, about 5000 light years away. 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 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.

Object information
Name : NGC6888 Crescent Nebula
Type : Nebula
Constellation : Cygnus
Distance : 5K light-year
Apparent dimensions : 18' x 12'
Apparent magnitude : 7.40

Image information
Image date : 2014/07/17, 2014/07/16, 2014/07/15, 2014/07/14, 2014/07/12, 2014/07/10, 2014/07/09, 2014/06/27
Right ascension : 20:12:7.069
Declination : 38°21' 21.76"
Focal length : 1686.32 mm
Focal ratio : f/6.64
Image resolution : 0.661 arcsec/pixel
Field of view : 36' 0.5" x 27' 10.8"
Sky quality : 21.50 mag/arcsecond2
Guiding rms : 0.3 arcsec
Sensor temperature : -20°C
Light frames : 35 hours total exposure time
12x 300 sec. RGB unbinned for star color
21x 1800 sec. hydrogen-α unbinned
24x 1800 sec. oxygen-III unbinned
19x 1800 sec. sulfur-II unbinned
Image acquisition with ACP Observatory Control Software, ACP Scheduler and Maxim DL
Auto-guiding with Maxim DL
Auto-focusing with FocusMax
Bias frames : 100x unbinned - SuperBias
Dark frames : None
Flat frames : 30x RGB unbinned
18x hydrogen-α unbinned
30x oxygen-III unbinned
18x sulfur-II unbinned
Automated sky twilight flats with ACP
Processing : PixInsight for calibration, alignment and integration.
Adobe Photoshop CS6 for final touch.

Equipment information
Telescope : Orion Optics 10" ODK
Corrector : None
Focuser : Baader SteelTrack with SteelDrive
Mount : Mesu Mount 200 with Sidereal Technology SiTech Controller
Camera : QSI 683wsg-8 cooled CCD camera with Kodak KAF-8300 sensor and Off Axis Guide (OAG) port
Guidecamera : Starlight Xpress Lodestar autoguider
Filters : Astrodon Tru-Balance E-Series LRGB & Astrodon 3nm H-α, 3nm O-III, 3nm S-II and 3nm N-II
Observatory site :, Hautes-Alpes, France