The Cygnus Wall

The Cygnus Wall is a turbulent region of star formation, and part of the much larger North America Nebula (NGC 7000). The Cygnus Wall is mostly made from Hydrogen and Sulfur, shown here in orange-red, surrounded by Oxygen, shown here as blue. The Cygnus Wall is about 20 light-years long, or put another way, about 1.3 million times further than the distance between the Earth and Sun!

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Askar 130PHQ: September 2023

I almost captured The Cygnus Wall in an earlier image of The Pelican Nebula, taken with my previous Askar FRA400 telescope. Part of my wanting to upgrade to my new Askar 130PHQ was to really focus in on parts of large nebulae, seeing details that are hard to get with a small-aperture wide-field telescope. So I was drawn to The Cygnus Wall because I knew it was a dynamic part of the night sky, and would fill my focal length of 1000mm very nicely.

The nights are starting to draw in and there was a spell of decent clear weather, which meant it only took me three weeks to collect 40 hours of data in total. 18 hours was Optolong L-Ultimate data. This looked fairly clean after integrating, which is always a good sign! The positive omens continued when I integrated 19 hours of Askar D2 data. This often looks quite a bit worse than the L-Ultimate, as it’s capturing Sulfur II instead of Hydrogen-alpha, and the signal is usually weaker. Although it was a bit noisy, I was happy to see a decent level of detail. And finally, I captured three hours of RGB (no filter) data. My plan was to just use this for true colour stars, but the nebulosity looked too good to chuck and I ended up including it in the final image by using PixInsight’s NBRGBCombination utility. You can see example raw subfames and freshly integrated data if you scroll down to “Example source data”.

So, this image is actually a mix of S H O and RGB, all from an OSC camera. Pretty neat! It’s fair to say the result could have been obtained faster (and perhaps better) using a mono camera and filters, but the required kit is more expensive and data acquisition would have been a bit more fiddly. In any case, I think the end result is very respectable, especially considering my light-polluted city-centre location.

I processed this image using the latest version of PixInsight (1.8.9-2). To begin with the software kept crashing and was basically unusable. The developers must have issued a patch though as after leaving it a few days and trying again it was much more stable. I think that the WeightedBatchPreProcessing (WBPP) function is a bit faster too. PixInsight has never been a speed-machine when it comes to making an integrated image, but these times are better than I’ve come to expect:

During processing, I had a particularly hard time putting the stars back into the image after pushing the nebulosity as far as I could. I used simple PixelMath (starlessimage+stars) but the stars looked very bloated, far more than they did in the star mask. I tried using ScreenStars, a new (free!) script by Bill Blanshan and Mike Cranfield. It was very good, and gave me nice tight stars as can be seen in this slider-comparison image. I’ll be using ScreenStars as a standard part of my workflow from now on.

Imaging details

* 25 August – 15 September 2023 (three weeks)
* Bristol, UK (Bortle 8)
* Telescope: Askar 130PHQ Flatfield Astrograph
* Camera: ZWO ASI 2600MC-PRO
* Mount: Sky-Watcher EQ6-R PRO
* Guide: William Optics 50mm Guidescope with 1.25″ RotoLock; ZWO ASI 120MM Mini
* Control: ASIAIR Plus
* Software: PixInsight, Lightroom
* Filters:
– Optolong L-Ultimate (Ha / OIII): 540 x 120 seconds (18 hours)
– Askar Colour Magic D2 (SII / OIII) : 570 x 120 seconds (19 hours)
– No filter: 90 x 120 seconds (3 hours)

Total exposure time: 40 hours

By Lee Pullen

Example source data

This image was used as the cover of the Winter 2023/24 issue of community magazine Up Our Street.

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