NGC 6946 & NGC 6939
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August 8, 2026
The two objects in this image each cover about 1/3 of the Moon’s diameter, but one lies about 6,000 times further away from us than the other. Open cluster NGC 6939 (upper right) lies within the Milky Way, our home galaxy, about 3,860 light years away. Galaxy NGC 6946 (lower left), sometimes called the Fireworks Galaxy, is around 22 million light years distant. Every star visible in this image is within our Milky Way galaxy, or in other words, in the foreground.
It’s easy to see why NGC 6946 is nicknamed the Fireworks Galaxy. The reddish star-forming regions are similar to the Orion Nebula in our own galaxy. We see NGC 6946 face on, so it’s possible to spot the dark dusty lanes between the blue arms full of stars, and within the golden centre. In addition to looking like a fireworks display, this galaxy has acted like one: there have been 10 supernova explosions observed in it since 1917, most recently in 2017. It would appear brighter if it wasn’t heavily obscured by our own galaxy’s dust lane. There’s likely a black hole gobbling up stars concentrated in the bright core of the galaxy.
NGC 6939 sparkles with a slightly reddish overall hue due its extreme age of 2.2 billion years. Most of its blue and white stars have exhausted their fuel and are no longer visible. I’ve glimpsed this open cluster in binoculars, and it is lovely in a telescope of any size. It is about 3,860 light years away.
This image includes a lot of Integrated Flux Nebula — reflections off dust and soot of the combined glow of the Milky Way’s stars. You can see this diffuse glow throughout the image. There are also dozens of galaxies throughout the image, mainly from the PGC catalogue. They’re marked in yellow in the annotated image. Quasars, identified in the MILLIQUAS catalogue, are shown in white. Zoom in to see these objects, some of which are more than 10 billion light years away.
One of my previous images of this region was the Space.com Image of the Day on October 12, 2018.
Tekkies:
Acquisition, focusing, and control of Sky-Watcher Wave 150i mount and other equipment with N.I.N.A. and Green Swamp Server. Primalucelab 3″ ESATTO focuser, ARCO rotator, GIOTTO flat panel and ALTO cover motor. Player One Xena-M guide camera, OAG and Filter Drawer MAX. Equipment control with Primalucelab EAGLE 6 Pro computer. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Acquired under above-average transparency and seeing and slight to moderatemoonlight from June 6 to July 12, 2026.
Sky-Watcher Esprit 120, Player One Poseidon-C Pro camera, Optolong L-Quad Enhance filter and L-eXtreme filter.
LQUAD 446 x 5m = 37hr 10m
L-eXtreme 44 x 5m = 3hr 40m
Total = 40hr 50m
Preprocessing: The WeightedBatchPreProcessing script was used to perform calibration, cosmetic correction, weighting, registration, integration and drizzle integration (2X).
Master images: The LQUAD master was renamed ‘RGB.’ A master Ha image was made by applying the Lighthouse NBExtract script to the L-eXtreme master. This was renamed ‘Ha.’
Gradient Removal: DynamicBackgroundExtraction was applied to the RGB and Ha masters.
Colour Calibration: BlurXterminator was applied to the RGB master with Correct Only selected, followed by ColorCalibration, using the galaxy as white reference.
Deconvolution: BlurXterminator was applied to the RGB and Ha masters with Automatic psf , star sharpening set to 0.5, and non-stellar set to 0.9. This was followed by the RepairStarCores script (2 pixels; threshold = 0.80).
Ha Continuum Subtraction: The Seti Astro Continuum Subtraction Utility was used to remove continuum emissions from the Ha master using the red channel of the RGB master as the continuum reference image. Starless images were used for this process.
Star Removal and processing: StarXterminator was used to remove the stars from the RGB master with Unscreen checked. The stars-only image was stretched with the Seti Astro StarStretch script. Colour was increased in the stars-only image by increasing saturation using CurvesTransformation through a star mask.
Stretching: MultiscaleAdaptiveStretch was applied to make pleasing images from the RGB and Ha masters. Approximate background level after stretch was 0.1 for the RGB master and 0.05 for the Ha master.
Nonlinear Processing
Noise Reduction: NoiseXterminator was applied to the RGB and Ha masters with settings Amount=0.9 and Interations=4.
Supplemental Stretch: HistogramTransformation was used to darken the black point and brighten the main galaxy.
Initial Saturation Boost: CurvesTransformation’s saturation tool was used to boost colour in the galaxy in the starless RGB image. A range mask made with RangeSelection was used to protect the background.
H-alpha Blending: The contiuum-subtracted Ha master was added to the RGB image using Jurgen Terpe’s CombineHaWithRGB script, using a mask to protect the background.
Nonlinear Noise Reduction: NoiseXterminator was applied to the HaRGB image with settings Amount=0.9 and Iterations=5.
Contrast Enhancement: LocalHistogramEqualization was applied five times using a mask to select or protect the main galaxy. For the galaxy, two iterations were applied with a Contrast Limit of 1.5 and 1 iteration (scale 150, strength 0.25, and scale 40, strength 0.35). For the background three applications were used, all with Contrast Limit of 1.5, 1 iteration, and strength=0.35 (scale 255 and 150). ExponentialTransformation was applied to the background while protecting the galay.
Sharpening: BlurXterminator was applied (no star reduction, no halo reduction, manual psf=3, amount = 0.1) to the galaxy, using a mask to protect the background.
Star Restoration: Stars were added back into the image using the PixelMath expression combine(starless, stars_only, op_screen())
Final Steps: Background, galaxy, and star brightness, contrast, and saturation were adjusted in several iterations using CurvesTransformation with masks as required. Excessive star haloes were dimmed slightly with CloneStamp. ICCProfileTransformation (sRGB IEC61966-2.1; Relative Colorimetric with black point compensation) was applied prior to saving as a jpg. The finder chart was made using the FindingChart process. The annotated image was made with the AnnotateImage script.
Absolutely beautiful.
You really captured a lot of the faint arm detail in this one, nice job keeping the flux during processing. Nice image!!