NGC7635 Bubble Nebula

NGC7635 Bubble Nebula (with M52 Cassiopeia Salt and Pepper Cluster), captured at HCH, Colorado Springs, CO with ASI2400MC#2, Big Bertha and LeXtreme LP filter; 29 September 2023

Fun facts

NGC 7635, also known as the Bubble Nebula, Sharpless 162, or Caldwell 11, is an H II region emission nebula in the constellation Cassiopeia. It lies close to the open cluster Messier 52 (also included in this image). The “bubble” is created by the stellar wind from a massive hot, 8.7 magnitude young central star, SAO 20575 (BD+60°2522).  The nebula is near a giant molecular cloud which contains the expansion of the bubble nebula while itself being excited by the hot central star, causing it to glow. It was discovered in November 1787 by William Herschel.

Other Catalog Designations: C11, NGC7635, SH2-162, LBN548, Ced210

Subtype: HII region, Emission Nebula
Distance from Earth:
 11090 light years
Apparent Size: 15’ x 8’

Constellation: Cassiopeia

{Target information derived from: and Stellarium }

Capture Notes:

Clear night (albeit full supermoon) gave me the chance to test out the new extension tube I finally was successful in convincing Orion that I needed, they admitted they had it in stock, and “allowed” me to purchase it.  Also, wanted to experiment with the Teleskop Field Flattener, that with the first try with the ASI2400MC had created more coma than it corrected.  I had looked up the design distance between the sensor and the flattener, the manufacturer said it should be “a generous” 109mm.  I measured from the glass plate (not sure how far back the sensor is from there) to the sensor side of the FF, it seemed in the range of 109mm, so I convinced myself that I must have used an extra sleeve of the connection tube in previous attempts.  Turns out that I had the same (worse coma with the FF than without) even with that recommended separation, so I stopped the sequence after one image, took off the FF, refocused, and restarted the sequence without the use of the FF. There is still some coma (which is annoying because I had intentionally framed the image to include the M52 cluster in the SE corner and the stars in the cluster are pretty coma-affected).  Other than that, the collection went remarkably well throughout the night.  The sequence did abort somewhere after 2333MDT (transit was 2347MDT).  I came out to do the meridian flip at about midnight, and was able to successfully restart the sequence (on the correct side of the meridian) without issue.  So the mystery of meridian flip +/- 15minutes continues… 


Polar alignment: QHYCCD camera (controlled by Polemaster)
Imaging stream: (Big Bertha) Orion 8″ f/8 Ritchey-Chretien Astrograph Telescope, ZWO ASI2400MC#2 imaging camera, Optolong LeXtreme light pollution filter
Mount: SkyWatcher EQ6‑R PRO Synscan mount (controlled by ASCOM driver)
Autoguider: Orion 60mm Multi-Use Guide Scope, Orion StarShoot AutoGuider Pro Mono Astrophotography Camera (controlled by PHD2)
All equipment controlled by Windows 11 HP Probook (DSO-CTRL-2) running Sequence Generator Pro v4.2.0.16.

Capture & processing notes

Sequence plan: Gain: 158, Temp: -0°C, offset=30, Bin: 1×1, 100x5min.  Total exposure time: 8:20hrs.
Captured: Captured 29Sep2023 2042MDT – 30Sep2023, 0547MDT. 
Shooting location: HCH, Colorado Springs, Colorado
Processing: Captured with SGP. Stacked in APP (HaOIII Color, HaOIII extract Ha, HaOIII extract OIII). Star removal with Starnet++. Processed in LR/PS. 

I performed the Ha and OIII extract algorithms and brought the results into LR and PS to use Nico Carver’s dual narrowband colorizing technique (3 Ways to edit Dual Narrowband Astrophotography! at a try with this image.  I ended up starting with my “standard” process (in quotes because I really have no standard – as each image is processed with a slightly different workflow) that includes using the Alyn Wallace presets ( That turned out with a satisfactory result (at least for now until I catch up on processing and planning). So, again, I’m calling this a “front patio placeholder” and adding to my “reshoot in dark skies” list…