Caldwell 23
Caldwell 23 - Click here for full resolution
Caldwell 23, also known as NGC 891, is a striking edge-on spiral galaxy located approximately 30 million light-years away in the constellation Andromeda. It is often compared to the Milky Way due to its similar size and structure. This galaxy is part of the NGC 1023 galaxy group. NGC 891 is notable for its thin, flat disk of stars, gas, and dust, which is sharply defined and spans about 100,000 light-years across. A prominent dust lane runs along its equatorial plane, obscuring parts of the galaxy and highlighting its intricate structure. One of the more fascinating features of NGC 891 is its extended halo of gas and dust, which suggests the presence of ongoing star formation and possible interactions with smaller satellite galaxies. Observations have also revealed filamentary structures extending above and below the galactic plane, likely caused by supernova explosions and stellar winds that eject material into the halo.
source: DeepSeek
NGC/IC:
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NGC891
Silver Sliver Galaxy
Galaxy
Andromeda
02h 22m 36s
+42° 21.0′
30 million ly
10.8
13 November
85º N
Conditions
C23 is best visible during Winter. Observed from the remote observatory at IC Astronomy in Oria , Spain, it reaches a maximum altitude of 85 degrees in mid November. C23 was photographed from that observatory over 6 nights during late December 2024 and January 2025.
Equipment
The default rig at the observatory was used. The core of this rig is a Planewave CDK-14 telescope on a 10Micron GM2000 mount, coupled to a Moravian C3-61000 Pro full-frame camera. The RoboTarget module in Voyager Advanced automated the process to find optimal time-slots during astronomical night.
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Planewave CDK14, Optec Gemini Rotating focuser
10Micron GM2000HPS, custom pier
Moravian C3-61000 Pro, cooled to -10 ºC
Chroma 2” Luminance, Red, Green and Blue unmounted, Moravian filterwheel L, 7-position
Unguided
Compulab Tensor I-22, Windows 11, Dragonfly, Pegasus Ultimate Powerbox v2
Voyager Advanced, Viking, Mountwizzard4, Astroplanner, PixInsight 1.9.2
Imaging
C23 is a typical broadband object, and default LRGB imaging parameters were applied. This means an exposure of 3 minutes for the luminance channel and 5 minutes for the red, green and blue channels. Overall, the total exposure time accumulated was 18.7 hours, with the total duration being approximately evenly split between the luminance and RGB exposures.
Resolution (original)
Focal length
Pixel size
Resolution
Field of View (original)
Rotation
Image center
9576 × 6388 px (61.2 MP)
2585 mm @ f/7.3
3.8 µm
0.30 arcsec/px
48' x 32'
-0.697°
RA: 02h 22m 32.723s
Dec: +42° 20’ 56.40”
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.
To get maximum flexibility of stretching the galaxy, stars were removed from both Lum and RGB. They were stretched and combined separately to be later added back in the final image.
Using careful stretching with GHS, a lot of detail could be extracted from the galaxy. Additional attempts to emphasise even more structure in the central dust lane of the galaxy with LocalHistogramEqualization, DarkStructureEnhance and/or UnsharpMask generally gave over-processed results and were not applied for the final image.
Normally I would crop in the final image to focus more on the galaxy. But in this case, there are a lot more small galaxies all over the image, that it felt a shame to crop them all out. So this image in particular is worthwhile to explore in the full resolution version.
The rest of the processing followed a pretty straightforward workflow.
Processing workflow (click to enlarge)
This image has been published on Astrobin
