Cygnus is high in the sky early November in the UK, in fact by midnight my imaging is almost done as Cygnus flies below the the western horizon. I managed about 5 hours but as we shall see low cloud/fog descended, not in the weather forecast (when is it ever!) and meant I threw away a large number of images.
The star Sadr (γ Cygni), named derived from the Arabic for 'chest' it's the 68th brightest by visual magnitude in the night sky and the second brightest, after Deneb in Cygnus. It is classified as an F8 Lab spectral type which means it is a Supergiant. Compare to the sun it is 12 times its mass and 150 times its radius, a big star. One of the interesting facts about stellar evolution is that the bigger they are the quicker they die as they get through their fuel so much quicker, Sadr is outputting 33,000 times more energy than the sun.
In the plate solved version of my image below the star is messily annotated with IC 1318 this is the referring to the Nebulosity of this whole region, you can see the diffuse nebular (the red areas) but this also refers to the lanes of dark dust that run through the image.
One other 'minor' item to point out is NGC 6910 which is highlighting the small open cluster. In terms of distances Sadr is 1,800 light years away, the IC 1318 is associated with Sadr and as such is the same distance, NGC 6910 is 3,700 light years away. This cluster although very faint would be a magnitude brighter if it was not for being obscured by the intervening dust.
The dark dust can be highlighted if the platesolve of my image is used to show the what this view would look like if imaged in the Infrared, infrared imagery shows much better dark clouds. The overlay above and below are produced via http://nova.astrometry.net with the Infrared provided by the Wide Field Infrared Survey Explorer.
Always interesting to note that what we see with normal camera sensors designed to emulate the human eye response to colour is just one small part of the electromagnetic spectrum.
Capture
2022-11-12
Exposure at ISO800, 240s using the Optolong L-Enhance Filter
Lights - 68
Darks - 10
Flats - 30
The Darks here were made up of 10 taken on a previous night at 9.3º, at the very start of imaging the temperature on the night was 10.3º.
Pre-Processing
Although 68 lights were taken it was obvious that fog had descended a couple of hours into the night, also another interesting problem was that the pier made the move to Cygnus on the left hand side of the pier which after about 1 hour of imaging triggered the protection alarm on the mount (designed to stop the camera colliding with the tripod). A reset and move to West Side of Pier was required and all was good. This caused about 1 hour of star trailed images due to the mount stopping its tracking because of the alarm.
Both of the above would have been caught earlier had I been sat with the mount outside in the weather... I prefer the automated approach of being inside in the warm peridically monitoring using either Remote Desktop to my imaging laptop or more recently via the web interface provided by a plugin of Nina which outputs graphs and thumbnails of images as they come in.
All the above said after manually removing I ended up with 25 Lights, 25*4m= 1h40m of exposure. I did attempt a pure filter based stack using my scripts and the usual 3.5 FWMH, 5 for wFWHM and Roundness of 0.8 but the overall picture was much hazier.
Post Processing (V2 stacked images)
Siril
After registration of all images (before the selection of the best 25) I ran a background extraction process on all registered images using a simple 1-order Polynomial model (straightforward Siril option). This was performed as there was a significant moon that evening and the fact that a side of pier (east->west) was performed meant that background extraction did not work well on the final image.
Crop - minor to remove stacking artefacts
Colour Calibration Photometry
Deconvolution, Kernal size of 1.1
Asinh Stretch - 3 iterations with stretches of (30,30,3)
Histogram Stretch
Green Noise Removal
Starless and Stars created using Siril Pixel Maths and Starnet++.
Once we have a TIFF (16 bit version) of Starless move into PS.
Photoshop (PS) Processing
Levels & Curves - Careful here not to overly balance the channels, doing this initially resulted in a rather bland yellow fire not the raging red this nebula is known for.
Raw - Highlights and Contrast
Raw - Texture
Raw - Clarity
Raw - Colour Contrast
Raw - Noise Reduction
Raw - Saturation and Vibrancy and Shadow
Create FIT version of TIFF file output from PS using Siril
Once back from PS then Pixel Math Add the Stars back into the FIT version of the PS processed TIFF file using the formulae (starless+(0.8*stars)).
Created JPG version.
Final Thoughts
Learning point I took away on this image:-
Side of Pier - to be honest on every other imaging session I have run I have never experienced this issue. I believe it is because previously most targets were started in the East and transitioned to the west which meant a Meridian flip would occur (controlled very well by N.I.N.A.) at which point the side of pier change is made. In this case the object had already past meridian and I had not changed the default of East Side of Pier - lesson, check if object is already on the West and if so move side of pier to West.
One of the major projects I would like to undertake in the future would be to take a multi-panel mosaic of this region, there are so many great objects (American / Pelican / Sadr / Crescent) that a single high resolution image would be fantastic. Come on Siril - make that Mosaic an option!
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