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I've been imaging Thor's Helmet for the last couple of nights in Ha and O3. I notice that RGB data can be used to correct star colour. What exposure is recommended to capture the stars and how many should I take? It looks as if I've one more clear night for the time being. Thanks Anne
I lost astro dark a couple of weeks back. I thought, therefore, that I would try capturing narrowband during nautical darkness on the basis that I may as well do something with all the gear. I ended up with 6 hours of Ha and 6 Hours of OIII captured at my home observatory using my Esprit 120 and QSI 690 atop a Mesu 200 mount. Filters are Astrodon and exposures were 30 minutes each. Processing in PixInsight and Adobe Photoshop. I cropped the image slightly to eliminate a couple of brighter stars at the edge of the frame. I'd be interested to hear what people think.
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.
This is the Pacman Nebula - 5 hours of Ha and 5 hours of OIII captured over 5 nights with my Esprit 120, QSI 690 and Astrodon filters. Some of the OIII nights were a little indifferent and a couple of OIII frames were discarded but most were kept. Combination was: Red - Ha; Green - 40% Ha plus 60% OIII; Blue - OIII. Processing in Pi and PS.
We have been battling a bit over that last few nights trying to gather data on a detail of the Eastern Veil nebula - a section known as the Bat. This is 20 minute Ha and OIII subs - 5 hours of Ha and 3 hours 40 mins of OIII. Esprit 120; QSI 690; Mesu 200 - Astrodon 3nm filters. All comments gratefully received.
For reasons unknown, we experienced a good night here last night. Indeed, I managed to get 5 hours of data during 'Astro Dark' - all of it with reasonable guiding. I had an hour of Ha from the previous evening. So this made 9 x 20 mins of Ha and 9 x 20 mins of OIII. All captured using the Esprit 120 and the QSI 690. Filters were 3nm Astrodons. I did my pre-processing in PixInsight. The stacks looked reasonable and I just 'kept going' in PixInsight. This is PixInsight with no Photoshop whatsoever, which is a first for me. It is reasonably clean but my original plan was to get at least 6 hours of Ha and OIII, and I may carry on with that. As usual, I'd appreciate comments and criticism.