SH2-157 – The Lobster Claw Nebula - 34.5 Hours of SHOrgb! Plus The Bubble Nebula!
Date: November 7, 2025
Cosgrove’s Cosmos Catalog ➤#0153
SH2-157, the Lobster Claw Nebula, captured through narrowband filters (Hubble Palette). The long 34.5 hour exposure reveals intricate, billowing clouds of ionized gas and dust around the young star cluster.(click image for hi-res version via Astrobin.com)
A deep 34.5-hour look at Lobster Claw and Bubble Nebula, side-by-side: a clear look at hot stars molding gas where new stars take shape.
🔭 Project Summary
Target: Sh2-157 – The Lobster Claw Nebula (+ vicinity of NGC 7635)
Capture Dates: October 16, 17, 26–28, 2025
Constellation: Cassiopeia • Distance: ≈ 8–11 thousand light-years
Type: Emission Nebula / H II Region
Imaging Period: October 16–28, 2025 • Total Integration: 34 h 30 m (SHO + RGB)
Filters: Ha (6 nm) · O III (6 nm) · S II (6 nm) · RGB
Telescope: Askar FRA400 f/5.6 Quintuplet Astrograph (400 mm)
Camera: ZWO ASI1600MM-Pro (−15 °C; Gain 139 NB/RGB)
Mount: ZWO AM5 on Custom Steel Pier
Processing: PixInsight (SHO starless + RGB stars) & Photoshop
Location: Whispering Skies Observatory · Honeoye Falls, NY (USA)
Acquisition notes: Narrowband 300-s subs; RGB 90-s subs.
The WIliam Optics 132 FLT APO Platform!
📸 Capture Details
Nights: October 16, 17, 26–28, 2025
| Channel / Filter | Frames × Exposure | Settings | Total |
|---|---|---|---|
| Hα — Astronomik 6 nm (1.25″) | 133 × 300 s | bin 1×1 • −15 °C • Gain 139 | 11 h 05 m |
| O III — Astronomik 6 nm (1.25″) | 132 × 300 s | bin 1×1 • −15 °C • Gain 139 | 11 h 00 m |
| S II — Astronomik 6 nm (1.25″) | 130 × 300 s | bin 1×1 • −15 °C • Gain 139 | 10 h 50 m |
| R — ZWO (1.25″) | 21 × 90 s | bin 1×1 • −15 °C • Gain 139 | 31 m 30 s |
| G — ZWO (1.25″) | 21 × 90 s | bin 1×1 • −15 °C • Gain 139 | 31 m 30 s |
| B — ZWO (1.25″) | 21 × 90 s | bin 1×1 • −15 °C • Gain 139 | 31 m 30 s |
| Total Integration (after culling): 34 h 29 m 30 s (SHO + RGB) | |||
Calibration Frames
- 30 × Dark frames @ 300 s, bin 1×1, −15 °C, Gain 139
- 30 × Dark frames @ 90 s, bin 1×1, −15 °C, Gain 139
- 25 × Dark-flats @ flat exposure times, bin 1×1, −15 °C, Gain 139
- Flats (one set): 15 each — Hα, O III, S II, R, G, B
Table of Contents Show (Click on lines to navigate)
🔭 About The Target
Sharpless 2-157 (Sh2-157), “The Lobster Claw Nebula,” is a broad H II complex in Cassiopeia, lying along the Perseus Arm at an estimated distance of ~8–9,000 light-years. The field is dominated by layered ionization fronts and wind-sculpted cavities that outline the “claw,” with the compact ring Sh2-157A, near WR 157, embedded on its southern rim. Several young clusters—most notably Markarian 50—and massive OB stars provide the ionizing radiation that shapes the nebula’s scalloped edges.
In the lower left of this frame sits NGC 7635 (The Bubble Nebula) around the O-star BD+60° 2522.. Located ~7,000 light-years away, it is a smaller but striking wind-blown shell set against the surrounding emission of the larger H II region. Together they form a physically rich scene of feedback, dense molecular material, and ongoing star formation spread over more than half a degree on the sky.
The surrounding emission region encompasses several Lynds Bright Nebula entries (notably LBN 533, 536, 537, 540, 544), reflecting how different bright patches within the complex were cataloged.
🗂️ History & Designations
Sh2-157 entered the literature in Sharpless (1959) as part of his second catalog of H II regions. The bright circular substructure is listed separately as Sh2-157A and is associated with the Wolf–Rayet star WR 157. It is also listed in some resources under the earlier Sharpless catalog as Sh 1-109; many catalogs cross-identify the complex with LBN 537. The bright ring substructure Sh2-157A is also explicitly identified as LBN 537 surrounding WR 157.
NGC 7635 (Bubble Nebula) carries multiple designations: Sharpless 162 (Sh2-162), Caldwell 11 (C 11), and LBN 549. Historically, it was discovered by William Herschel (1787); modern observing guides and catalogs retain the LBN and Sharpless cross-IDs.
👁️ Visual Observations
Sh2-157 is large and has a low surface brightness. Under dark, transparent skies, a UHC filter enhances the diffuse glow, while an O-III filter crisps up the brightest arcs; H-β is generally weak. In 10–12″ apertures, trace the main scalloped rim at low–moderate power (3–5 mm exit pupil). 16–20″ instruments reveal interior ribbing and the compact Sh2-157A/LBN 537 patch near WR 157. NGC 7635 (Sh2-162/C11/LBN 549) is a small but high-contrast object; an O-III filter at 150–250× best outlines the bubble rim against the surrounding H II region. A 1.5–2.0° field frames both objects with context.
🔬 Science
Sh2-157 is an active star-forming complex where massive-star feedback (UV flux and winds from OB stars and WR 157) drives ionization fronts, carves cavities, and compresses adjacent molecular gas; YSO candidates concentrate along bright rims consistent with triggered star formation. NGC 7635 (Sh2-162/C11/LBN 549) is a textbook wind-blown bubble: the fast, supersonic wind from BD+60° 2522 sweeps up the ambient medium into a thin shell; the brightest limb marks interaction with denser molecular gas.
Annotated Image
Created in Pixinsight using the ImageSolver and AnnotateImage scripts.
The Location in the Sky
This annotated image created with ImageSolver and FinderChart Scripts in Pixinsight.
About the Project
Planning and Weather
The data for this target were collected during the last lunar cycle, when we had a spate of five fairly clear nights.
Some of the details here are the same as for my previous project, NGC 7830 - The Wizard Nebula, so I will repeat that section here:
Finally, we have those wonderfully long fall nights with almost 11 hours of darkness!
During the last lunar cycle, I ended with five clear nights to capture data. However, on four of those nights, the weather apps indicated that it would not be very clear. In the past, this would have been enough to have me skip the night. It did not sound like it would be worth the effort to set up all that gear! But not that the observatory is up and running - I have no gear to set up! Yay! This means I am much more willing to go after those questionable nights.
I have an astro friend who is a weather buff (I’m looking at you, Gary Opitz!). Gary is an accomplished astrophotographer, and he scans the weather, consults government weather satellite data, and makes his own estimate of how the night will go. He also shares that info with our small local group of astrophotographers and even gives us updates throughout the night. How great is that!
The apps told me it would be a questionable night, but Gary said our chances looked good - so on Gary’s word, I went for it!
I ended up with four nights that were clear all night and one that was good for half a night.
I never know how the weather will go, so I typically research objects I can shoot with each scope - just in case. I chose four to begin with, and the Lobster Claw was one of those.
So, why did I choose it?
It is a large, faint, and challenging target.
I first shot this on Dec 29th, 2021, with an integration of only 4 hours - I wanted to see what I could do with a longer integration.
I thought the results of that effort were modest at best, but to my surprise, it has had more visits than any other imaging project I have done! While I am not sure why this is true, if there is that much interest, I felt compelled to provide a better image for it!
It was a very large object, and it was a perfect fit for my small FRA400 Platform.
The First Attempt
The first time I shot this was in one of those extremely rare (at least around here) clear nights in late December of 2021. I only captured about four hours of data on it, and since this target is large and faint, the image was a bit marginal at best. You can read about that project here:
During the cloudy months of February 2024, when I was bored with the lack of new data, I decided to take another crack at the old data and see if I could improve it. Same data, just new tools (starless processings, RC_Astro wonder tool, etc). You can read about that effort below:
SH2-157 Reprocessing Project in 2024
Here are the two images for comparison:
My first attempt with this target was done in Dec of 2021.
In 2024, I reprocessed the old data and really improved the image I think.
I was happy with the first image at the time because I got “something” despite the low integration. The reprocessed image offered a dramatic improvement I thought - at least with the color.
But the new image with 34.5 hours of integration beats them both!
Data Collection
Data was collected on the nights of October 16, 17, 26, 27, and 28, 2025.
The nights were cold enough that I could set a camera cooling target to -15 degrees C, and I knew the cameras could handle it. I set things up to do 300-second narrowband exposures with a camera gain of 139.
On the fourth night, I added RGB filter collection with 90-second subs and a gain of 139 to the mix.
The NINA sequence handled things very well, and my tracking looked consistently good.
My comments from the last post fit here as well so I will repeat them:
I find that I spend very little time in the observatory now on these cold nights. I go there to open the roof and uncap the scopes. Then everything else is handled remotely from my nice warm astro man cave. From there, I connect the devices to NINA and kick things off. That’s about it. NINA uses Pushover to send me alerts if necessary. I have a sofa in my Astro Man Cave, so I sleep there and check on things if I get a Pushover notification or if I am up for a bio-break. In the morning, I go back to the observatory, cap the scopes, and close the roof!
On two of the nights, I experienced frost, and each night we had a significant amount of dew. Fortunately, my anti-dew strips handled that perfectly. That was not true on all of my scopes, and I share that tale when I get to those images.
The moon was getting bright on the night of October 28th, but set relatively early. However, I knew that the next night, the moon would start causing problems with my data collection, which was nearing its end. Additionally, rain had moved into the area, and there was no further opportunity for data capture.
On the night of Oct 29th, I collected all of my calibration data, and with that in hand, I was ready to process this image.
Processing Overview
The processing for this image turns out to be very similar to my previous project. The target and the equipment are different, but both images were SHO images with RGB data for the stars. So it's not a surprise that there is similarity.
I decided against Drizzle processing as I thought the base resolution was enough to do justice to this target.
I blinked the data and removed a very small handful of frames due to thin clouds or obstruction when the target had set. Even after this, I ended up 30 seconds shy of a full 35 hours of integration! This is my longest yet!
Since I had collected both Narrowband and RGB data, I used my standard processing workflow for this case. You can see a high-level view of this workflow in the diagram below.
My typical SHO Starless Workflow with RGB stars.
The processing was pretty straightforward. With 25 hours of integration, the noise was manageable but not as clean as my last project. I think the reason for this is the difference in the camera. The 2600 series handles noise better than the older 1600 series that was used here.
I did my standard linear process for RGB and Narrowband. This results in a starless narrowband image of the nebula and a stars-only RGB image.
When I took star images nonlinear, I again chose three levels of stars - from smallest to largest - so that I could later determine which one looked better in this image. I again chose the smallest stars, as they looked better to my eyes.
With the nonlinear image, I created a WarmMask and a CoolMask. This allows me to adjust the tone and color of these regions selectively. Typically, I also tend to do more sharpening or contrast enhancement in the Warm regions. I tend to find that cool regions don’t do well with sharpening, and I stay away from it here.
I also created a few gradient masks with the GAME script so I could selectively adjust some image areas
Detailed and Annotated Image Processing Walkthrough
Typically, I conclude one of these imaging projects by documenting the processing steps I used on this image. But this section can make the overall post very large and, at times, slow to load.
I am now creating a secondary, standalone page to hold this information. You can access this page by clicking the link below. Returning to this page is as simple as clicking the back arrow in your browser or selecting a different menu option at the top of the page.
I hope you like this new format!
Hit the Link below to see the detailed image processing walkthrough page for this Imaging Project!
Final Results
At the end of the day, you simply cannot beat long integration times.
Each of the last few imaging projects I have done from the observatory has had increasingly longer integration times, but 34.5 hours is a significant record for me, and the results are evident in the image. The colors are nice and bright (some might say they are too saturated, but I am a high-color guy, so they reflect my style), and I am very pleased with the improved image detail seen here and how well the Bubble Nebula looks in the same frame.
What are your thoughts? I’d love to hear them!
More Information
🔭 Target Details
SIMBAD: Sh 2-157 (Lobster Claw) – Object record with identifiers, basic data, bibliography, and links to catalogs for the SH2-157 H II region.
SIMBAD: NGC 7635 (Bubble Nebula) – Database entry for the Bubble Nebula with cross-identifications (a.k.a. Sh2-162/Caldwell 11) and literature references.
Aladin Lite: Sh 2-157 (interactive sky view) – Pan/zoom, switch surveys, and overlay catalogs centered on SH2-157.
Aladin Lite: NGC 7635 (interactive sky view) – Same tool, centered on the Bubble Nebula.
NASA Science: Bubble Nebula (NGC 7635) – Mission page with distance/size figures and downloadable assets.
📜 History & Naming
Sharpless (1959): A Catalogue of H II Regions (ADS full text) – The definitive SH2 catalog that gives SH2-157 its primary designation.
Sharpless catalog (overview) – Background on the 1953/1959 editions and scope of the Sh2 list.
Bubble Nebula (NGC 7635) – overview – Discovery (William Herschel, 1787), alternate names (Sh2-162/C 11), and basic properties.
HubbleSite (2000): An Expanding Bubble in Space – Early HST release describing the wind-blown shell morphology of NGC 7635.
Christopoulou et al. (1995): Kinematics of NGC 7635 – Classic study on the shell’s velocity field and relation to the S 162 complex.
🔬 Science & Observations
Toalá et al. (2020, MNRAS): The Bubble Nebula – testing the wind-blown bubble model – Stellar-wind modeling of BD+60° 2522 and constraints on the shell/ambient medium.
Rauw et al. (2003, A&A): Line-profile variability of BD+60° 2522 – Spectroscopic behavior of the O-type driver of NGC 7635.
Jäger et al. (1987, IAUS): BD+60° 2522 and its interaction with S 162 – Early discussion of the central star’s wind and nebular interaction.
Tapia & Persi (2023, MNRAS): IRAS 23139+5939 and its relation to Sh2-157 – Embedded massive star formation and UC H II sources within the SH2-157 complex.
Vazquez et al. (2008, arXiv): Multifrequency study of ring nebula SG 13 in Sh2-157 – Radio/IR analysis of a related ring nebula (WR 157 environment) inside the field.
💡 Interesting Facts & Outreach
APOD (2024-10-30): NGC 7635 – The Bubble Nebula – Recent APOD featuring the Bubble’s 10-ly shell against the Cassiopeia/Cepheus complex.
APOD (2017-10-26): Bubble in a Cosmic Sea (with Sh2-157) – Wide-field composition that frames the Bubble and highlights the nearby “Claw” (Sh2-157).
APOD (2018-04-19): The Bubble Nebula – HST-based rendition describing the O-star driver and shell dynamics.
ESA/Hubble: The Bubble Nebula – ESA’s feature page with downloadable media and concise object facts.
Capture Hardware
Scope: Askar FRA400 72mm f/5. 6 Quintuplet Air-Spaced Astrograph
Focus Motor: ZWO EAF 5V
Guide Scope: William Optics 50mm guide scope
Guide Scope Rings: William Optics 50mm slide-base Clamping Ring Set
Mount: ZWO AM5
Tripod: Custom Steel Pier - New
Camera: ZWO ASI1600MM-Pro
Camera Rotator: Pegasus Astro Falcon Camera Rotator
Filter Wheel: ZWO EFW 1.2 5x8
Filters: ZWO 1.25” LRGB Gen II, Astronomiks 6nm Ha, OIII,SII
Guide Camera: ZWO ASI290MM-Mini
Dew Strips: Dew-Not Heater strips for Main and Guide Scopes
Power Dist: Pegasus Astro Powerbox Advanced
USB Dist: Pegasus Astro Powerbox Advanced
Polar Alignment
Cam: PoleMaster
Computer: Mele Quiert-4C Fanless microcomputer running Windows 11
Software
Capture Software: PHD2 Guider, NINA
Image Processing: Pixinsight, Photoshop - assisted by Coffee, extensive processing indecision and second-guessing, editor regret, and much swearing…..
Version 2.1 of my Askar FRA400 Platform consists of a switch to a steel pier in the Southeast corner of my new Whispering Sies Observatory. Also changed was the computer from a laptop to a new Mele Quieter 4C mounted on the pier.