NGC6888 Crescent Nebula

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2013/05/27 - I shot some extra data of The Crescent with the 10" RC and combined it with the data I shot last year with the 10" Newton.I also tried out the AAG CloudWatcher in combination with CCDAutoPilot to be able to pause the imaging session when clouds pass by. At the end of the night clouds were detected and the session was stopped.

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 : 2013/05/27, 2012/05/27
Right ascension : 20:12:8.498
Declination : 38°20' 55.31"
Focal length : 1381.34 mm
Focal ratio : f/5.44
Image resolution : 0.806 arcsec/pixel
Field of view : 42' 58.7" x 31' 52.6"
Sky quality : 19.46 magnitude/square arcsecond
Sensor temperature : -25°C
Light frames : 6 hours and 43 minutes total exposure time
3x 120 sec. RGB unbinned (starcolor)
5x 900 sec. + 3x 1200 sec. hydrogen-alpha unbinned
5x 900 sec. + 3x 1200 sec. oxygen-III unbinned
5x 900 sec. + 2x 1200 sec. sulfur-II unbinned
Session 2012:
Image acquisition scripted with Nebulosity v3
Auto-guiding with PHD (medium dither, settle < 0.3)
Session 2013:
Image acquisition automated with CCDAutoPilot and Maxim DL
Auto-guiding with Maxim DL
Auto-focusing with FocusMax
Bias frames : 100x unbinned
Dark frames : None
Flat frames : 6x RGB unbinned
6x hydrogen-alpha unbinned
6x oxygen-III unbinned
6x sulfur-II unbinned
Automated twilight sky flats with CCDAutoPilot
Processing : PixInsight for calibration (bias frames and flat frames), alignment and integration.
Adobe Photoshop CS6 for final touch.

Equipment information
Telescope : Robtics 10" 2000mm f/8 Ritchey Chretien
Corrector : Astro-Physics CCDT67 Focal Reducer
Focuser : Moonlite CS Ritchey Chretien focuser with high resolution stepper motor
Mount : ASA DDM60 Pro direct drive german equatorial mount controlled with AutoSlew
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 : Etten-Leur, The Netherlands