Discovered in 1792 by Friedrich Wilhelm Herschel, the Crescent Nebula (NGC6888, Caldwell 27, LBN 203, Sharpless 105), also known as "Van Gogh's Ear" is a magnitude 7.40 emission nebula in the constellation Cygnus (The Swan). It is formed by the violently fast stellar winds emanating from a Wolf-Rayet star (WR 136, HD192163) colliding with the slower gases that were shed by the same star many thousands of years ago when it was a red giant. The gaseous shell is approximately 25 light-years across and 5,000 light-years distant. It is predicted that the central Wolf-Rayet star will eventually explode into a supernova in approximately 100,000 years.
This image is in the synthetic RGB palette as detailed by Richard Crisp. Red = 100% H-alpha + 33% SII, Green = 100% OIII, Blue = 100% OIII + 33% H-alpha.
Telescope: Sky Watcher Quantum 120 Apo @ f/7
Accessories: SW Quantum matched flattener; Dew control by Dew Buster; Alnitak Flat-Man; Gerd Neumann Aurora flat panel
Mount: Takahashi EM-200 Temma2
Camera: QSI583wsg CCD @ -10.0C
Guiding: Starlight Xpress Lodestar via PHD
Filters: Astrodon 5nm Ha, OIII, SII
Exposure: 12 x 20min. binned 1x1 each in Ha, OIII, SII
Acquisition: ImagesPlus 5.0 Camera Control
Processing: PixInsight 1.8; Adobe PhotoShop CS5; Noel Carboni’s Actions
Date(s): June 3, 12, 13, 14, 2013
SQM reading (begin - end): N1:19.11 – 19.28; N2:18.92 – 19.15; N3:18.92 – 19.54; N4:18.89 – 19.39
Temperature (begin - end): N1:65.4ºF – 61.6ºF; N2:83.7ºF – 80.6ºF; N3:73.8ºF – 67.1ºF; N4:70.7ºF – 64.9ºF
Capture conditions: N1 - transparency: Avg 3/5; seeing: Avg 3/5; N2 - transparency: Above Avg 4/5; seeing: Poor 2/5; N3 - transparency: Above avg 4/5; seeing: Poor 2/5; N4 - transparency: Avg 3/5; seeing: Avg 3/5
Location: Hendersonville, TN, USA