The Clamshell Nebula
Sharpless 2-119 • Emission nebula • Cygnus • 2200 light-years from Earth
🔭
Askar 130PHQ
📷
ZWO 2600MC Pro
🌃
Bortle 8
⏱️
37 hours
🗓️
Sep – Oct 2024
Overview
The Clamshell Nebula, also known as Sh2 119, is an emission nebula located around 2200 light years away in the constellation Cygnus. This image focuses on the central region of the nebula, where complex clouds of gas and dust are being shaped by intense stellar winds and ultraviolet radiation from nearby hot, massive stars. Much of this structure is driven by the supergiant star 68 Cygni, visible here as the bright point toward the lower right of the frame.
Background
I’ve wanted to image the Clamshell Nebula for quite a while. For some reason I’d always assumed it was quite small, so I was surprised to find that it’s actually more of a wide-field target. Still, I wanted to give it a crack, so decided to leverage my Askar 130PHQ‘s 1000mm focal length to zero in on a composition around the centre of the nebula.
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Explore the field
Objects in this field 12 objects
12 objects
No matching objects.
- Clamshell NebulaSh2-119
- HII regionAlso catalogued as LBN 391 · LBN 400
- 68 CygniA Cyg
- Variable starAlso catalogued as 68 Cyg · V1809 Cyg · HR 8154 · HD 203064 · HIP 105186
- A hot, massive star illuminating the Clamshell Nebula.
- LBN 401
- HII region
- LBN 402
- HII region
- Ou 5
- Planetary nebulaAlso catalogued as PN G086.9-03.4
- LBN 389
- HII region
- LDN 949
- Dark nebula
- LDN 943
- Dark nebula
- LDN 942
- Dark nebula
- LDN 944
- Dark nebula
- LDN 946
- Dark nebula
- LDN 952
- Dark nebula
About the labels and credits
Positions and outlines are calculated from a plate solution of this photograph. Outlines are catalogue guides and may not follow every visible filament. Additional catalogue objects may be faint or indistinct in this exposure.
Plate solving and annotation data: SkySolver, by Dominik Sito. Stars: Gaia DR3 and Hipparcos (ESA). Deep-sky data: OpenNGC © Mattia Verga (CC BY-SA 4.0), SIMBAD and VizieR (CDS). Names: Wikipedia (CC BY-SA 4.0) and IAU WGSN. Catalogue overlay adaptations, including styling and selected display names, are shared under CC BY-SA 4.0. Photograph © Lee Pullen.
Kit list
This is the equipment I used to capture the image.
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Telescope: Askar 130PHQ
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Camera: ZWO ASI 2600MC Pro
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Mount: Sky-Watcher EQ6-R Pro
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Guidescope: William Optics 50mm with ROTO Lock
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Guidecam: ZWO ASI 120MM Mini
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Control: ASIAIR Plus
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Filter: Optolong L-Ultimate
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Processing
As usual for these types of nebulae, I used an Optolong L-Ultimate for Hα/OIII data, and an Askar D2 for SII/OIII. I normally use an Optolong L-Quad Enhance for RGB data — in this case just the stars — but I actually forgot to use it this time! It doesn’t really make much difference for the stars though, as they’re bright and use just an hour of integration time.
As for the L-Ultimate, that’s 12 hours of data. I knew the SII/OIII component would be fainter, so I doubled that and collected 24 hours. Unfortunately, the SII/OIII was even weaker than I expected. This caused some issues during processing (outlined below) so I needed to take a slightly different approach.
If I were to tackle this target again, I’d be tempted to forego the SII/OIII aspect, and just aim to get a very high signal-to-noise ratio with the Hα channel. As it stands, it’s a really tricky target with an OSC set-up from a city centre. It may be a more realistic approach with full Mono, and definitely with darker skies!
I don’t have time for a full processing walkthrough this time, but the first steps are the same as I followed for the Wizard Nebula. The main difference came after running DBXtract to make an SHO image from the Hα/OIII and SII/OIII data. The SII/OIII channel was so weak / noisy in comparison to the Ha/OIII, I just couldn’t get a high quality result. So, I decided to try something new. I used NarrowbandHueCombination to mix together the Hα, SII, and OIII channels produced by DBXtract.
Check the image below to see the settings I used. I used red at Contribution 100 for the Hα channel; but Contribution 0.5 for both OIII (blue) and SII (green). This made the stronger Hα channel much more dominant. The end result isn’t as colourful as I’d initially planned, but the actual image quality was higher, in that it wasn’t ridiculously noisy.
After that, I used SelectiveColorCorrection to make the red, orange, and yellow colours a bit more distinct. Then it was a case of my usual processes, including UnsharpMark, NosieXTerminator, and DarkStructureEnhance.
Here are two images I initially made using my regular method. The don’t look so bad when viewed small, but when viewed original size on my screen I just wasn’t happy with the image quality.
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Example source data
Here are example single subframes and freshly integrated stacks, just with simple stretches applied.
Seestar S50 image
This photo of the Clamshell Nebula was taken using my Seestar S50 telescope. It’s hard to make out much nebulosity, but the bright star 68 Cygni shows up well.
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