Sh2-230
Sh2-230 - Due to limitations of this website platform, the resolution of the above image is ‘only’ 60MP. For full resolution, click here for the 240MP version.
Sharpless 2-230 (Sh2-230) is an H II region in the constellation Auriga, approximately 6,800-9,800 light-years from Earth. The nebula spans 16–26 light-years in diameter. Infrared surveys reveal ongoing star formation in this and adjacent nebulae. The large region known as Sh2-230, and covered by this image is listed in Steward Sharpless’ second catalogue of 313 objects with the title "A Catalogue of H II Regions". However, within this region, there are many more, often better known objects, including two Messier objects and several other Sharpless II objects. See below for more details on them.
source: DeepSeek
NGC/IC:
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Object:
Constellation:
R.A.:
Dec:
Distance to Earth:
App. Magnitude:
Transit date:
Tr. Alt (Oria, Spain):
n.a.
n.a.
HII region
Auriga
05h 22m 30s
+34° 08.0′
6,800-9,800 ly
n.a.
20 December
71º S
Explore
Sh2-230 is a large area, but within that area, there are many other noteworthy objects. There are no less than two Messier objects and four other Sharpless II objects within the scope of this extended nebula. These objects include Sh2-236 (Tadpoles nebula, IC410), Sh2-229 (Flaming star nebula, IC405), Sh2-234, Sh2-237, Messier 36 and Messier 38. Click on the image to the right for a full resolution version and explore the details of each individual object by zooming and scrolling.
For smaller resolution versions, scroll through the image below and learn more about some these beautiful nebulae and clusters.
Conditions
Sh2-230 is easiest to see in winter. From The Netherlands, it can reach over 70° in the sky. It was photographed from the backyard observatory in Groningen during several clear nights in a row, which is unusual nowadays. Unfortunately, the bright moon interfered with the imaging, with angular moon distance in the 20-30° range. On two nights during this clear spell, the object was about 10° from the moon, and no images were taken then. Even narrowband imaging has its limits with the moon nearby. In total images were taken on four different nights in early March 2025.
Equipment
The rig used for this image consisted of a Takahashi FSQ-106, in combination with a ZWO ASI6200MM-Pro full-frame camera. Sh2-230 is a very large object, and in order to capture the majority of it, the focal length of the telescope had to be brought down. This was done by including the Takahashi 645 super reducer. Its 0.72x magnification factor brings the focal length of this telescope down to 382 mm. The 10Micron GM1000HPS mount allowed for unguided imaging. A Linux version of KStars/Ekos was used to automate the imaging process. The system has seen a few upgrades. The Sesto Senso focuser was replaced with the Pegasus Astro Motor Focus Kit v2. The Primalucelab rings were replaced by a Takahashi cradle. And the original Chroma filters from my ASI6200 had gone to the remote site, and had to be replaced. I decided on a set of Antlia filters instead.
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Takahashi FSQ-106, 645 Super Reducer-QE 0,72x, Pegasus Astro Motor Focus kit v2
10Micron GM1000HPS, EuroEMC S130 pier
ZWO ASI6200MM Pro, cooled to -15 ºC
Antlia 2” unmounted Ha and OIII (3nm), ZWO EFW 7-position
Unguided
Fitlet3, Pegasus Ultimate Powerbox v2, DeepSkyDad Flatpanel FT1 (30cm), Pegasus Uranus
Linux Mint 21.1, KStars/Ekos 3.7.5, INDI Library 2.1.2, Mountwizzard4 3.2.7, PixInsight 1.9.2
Imaging
Given the moon presence, narrowband imaging was preferred over broadband imaging. Therefore Sh2-230 was chosen. Sh2-230 is a typical HII object, and is best photographed using H-alpha narrowband filters. There is pretty much no SII signal present. There are a few regions (Sh2-236 and to a lesser extend Sh2-229) that have some OIII signal. So the decision was made to photograph this as an HOO image. At the start of the project it was unknown how many clear nights we would get, so I decided not to bother with RGB stars. Instead, proper star colours would be obtained during post-processing from the Ha and OIII signal. For this bottle 4-5 area, 5 min subs for narrowband images have generally proven to be sufficient. A total of almost 15h of exposure was collected.
Resolution
Focal length
Pixel size
Resolution
Field of View
Rotation
Image center
19152 × 12728 px (244 MP, after drizzling)
382 mm @ f/3.6
1.88 µm (after drizzling)
1.018 arcsec/px
5d 24' x 3d 35'
-31.2°
RA: 05h 22m 29.060 s
Dec: +34° 08’ 18.56”
Processing
All images were calibrated using Darks (50), Flats (50) and Flat-Darks (50), registered and integrated using the WeightedBatchPreProcessing (WBPP) in PixInsight. All further processing was done in PixInsight, including the use of scripts and tools developed by RC-Astro, SetiAstro, GraXpert, and others. For a step-by-step description of the processing techniques applied, see process flow below.
The 645 Super Reducer-QE 0,72x from Takahashi is an impressive piece of glass, but unfortunately, it is certainly not free of distortions towards the edges of the frame on a full-frame camera. Fortunately the star correction capabilities of BlurXTerminator do a fantastic job to bring star shapes back to pretty decent round stars, all the way to the edges. Another effect of the reducer is that the already fairly high pixel scale of the FSQ-106 is increased even more. With the 0.72x reducer, the pixel scale is 2 arcsec/pixel. This makes for some pretty blocky stars. Therefore I applied during the WBPP process a 2x drizzle. The improvement in image quality is amazing. Also this means that the 60MP files have now increased to a whopping 240 MP. This requires a bit more computing time during all the processing steps, but the results are definitely worth it. Keep in mind that due to limitations of this website builder, the maximum resolutions of images is 60MP. So to fully appreciate the nuances of the image, please check out the full resolution version.
To combine the H-alpha and the OIII channels, I tried different methods, including NarrowbandNormalization, NBColourMapping, manually stretching and combining the images, etc. But I never ended up with a pleasant colour palette. Often it was too red, the OIII did not come out well, etc. Eventually I tried the ForaxxPaletteUtility, developed by Paulyman Astro. This came out remarkably nice straight out of the tool, much better than the other attempts. I had not used it for a while and forgotten a bit how nicely it worked. But it is definitely something to try as an alternative to other methods
Because of the uncertainty about how much exposure time I would be able to get, I did not make RGB subs. So the stars had to be compiled from the H-alpha and OIII data. This can also be done through the same ForaxxPaletteUtility tool. I decided to follow that up with a proper colour calibration using SPCC. The stars came out quite nice. Perhaps somewhat less intense colours. I could have changed that by adding in more saturation, but decided to leave it as is, as there is already so much colour in the image.
To most images I apply a bit of a boost at the end, to add some contrast or colour. But in this case it was the other way around and the final image was toned down a bit, bringing selectively down the reds, and reducing overall saturation.
Processing workflow (click to enlarge)
This image has been published on Astrobin
