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Had my first go at this target in narrowband with the QHY5L-II-M. Was very skeptical if i could use the extremely faint and noisy OIII data at all, but i think it did somehow work, although it's a bit on the noisy side. all in all i'm very happy with the result, especially for my first attempt. Not sure if i made the proper color balance though? Any tips and thoughts are welcome. Captured with the QHY5L-II-M at 50% gain, unguided with a 135mm F/3.5 Olympus lens. 100x 120sec OIII 47x 120sec Ha
The Crescent Nebula NGC 6888 The Crescent Nebula rides on the Swan’s neck in Cygnus in a dense swathe of Milky Way stars - an ideal target for my first bi-colour image with my new Astrodon 3nm Ha and OIII filters and Esprit 150 telescope. The nebula was discovered by William Herschel on 15th September, 1792 and he described it as ‘A double star of the 8th magnitude with a faint south preceding milky ray joining to it.8’ long by 1.5’ broad’. This double star is not the prominent star with an apparent companion close to the heart of the nebula, rather, it is ADS13515 at the 2 o’clock position on the nebula’s bright periphery. The bright star off-centre of the nebula is particularly significant as this is the star that is powering the emissions from the surrounding gas cloud. This magnitude +7.5 star, HD192163, is of the Wolf-Rayet type and is also designated WR-136. Charles Wolf and Georges Rayet first described wolf-Rayet stars in 1867 following detection of their broad emission lines. The Wolf-Rayet stage applies to stars with an original mass in excess of 30 times our own Sun’s mass. This stage comes late in the star's evolution when a rapidly expanding shell of hot gas is powered outwards by the stellar wind only to collide with the much slower-moving gas clouds that were ejected thousands of years previously when the star entered its Red Giant phase. These forceful collisions produce a shock wave that generates an enormous amount of energy including wavelengths within the light spectrum, allowing us to observe them. This complex process displays as an arc of bright nebulosity that we identify as the Crescent Nebula. Long exposure images fill in this arc producing a crab-shell shaped nebulous region rich in Hydrogen Alpha and doubly ionised Oxygen emissions. WR-136 is fated to go supernova at some time in the future – watch this space! Image Stats Mount: Mesu 200 Telescope: Sky-Watcher Esprit 150 ED Pro CCD Camera: QSI 683 WSG-8 Sampling: 1.04”/pixel Guiding: OAG/LodeStar Filters: Astrodon 3nm Ha and 3nm OIII Exposure: 30 x 1800 sec Ha, 15 x 1800 sec OIII Date: 11/06/17 + 19/06/17 – much of which was under Lunar illumination Calibration: Bias, Darks & Flats Object Stats RA: 20° 12’ 04.6” Dec: 38° 30’ 46.0” Magnitude: +10.0 Distance: 4700 light years The Crescent Nebula – NGC 6888 Comparison of Ha and OIII data We imagers (well me anyway!) tend to think that Ha is the all-powerful emission line in nebulous objects but it is interesting to compare the Ha and OIII data for this structure as there is an enormous amount of OIII emission present in The Crescent Nebula.