Caldwell 30
NGC 7331
30’ x 20’ | 0.3”/px | 6000 × 4000 px | full resolution
Pegasus
RA 22h 37m Dec +34° 25’ | +65°
Caldwell 30, also known as NGC 7331, is an unbarred spiral galaxy about 43.79 million light-years away in the constellation Pegasus. It was discovered by William Herschel on 6 September 1784. The galaxy appears similar almost in size and structure to the Milky Way, and is sometimes referred to as "the Milky Way's twin". However, discoveries in the 2000s regarding the structure of the Milky Way may call this similarity into doubt, particularly because the latter is now believed to be a barred spiral, compared to the unbarred status of NGC 7331. In spiral galaxies the central bulge typically co-rotates with the disk but the bulge in the galaxy NGC 7331 is rotating in the opposite direction to the rest of the disk. In both visible light and infrared photos of the NGC 7331, the core of the galaxy appears to be slightly off-center, with one side of the disk appearing to extend further away from the core than the opposite side. NGC 7331 is the brightest galaxy in the field of a visual grouping known as the NGC 7331 Group of galaxies. In fact, the other members of the group, NGC 7335, NGC 7336, NGC 7337 and NGC 7340, lie far in the background at distances of approximately 300–350 million light years. All of the members of the NGC 7331 Group, along with additional galaxies NGC 7325, NGC 7326, NGC 7327, NGC 7333, NGC 7338, are listed together as Holm 795 in Erik Holmberg's ‘A Study of Double and Multiple Galaxies Together with Inquiries into some General Metagalactic Problems’, published in 1937.
source: Wikipedia
Data Acquisition
Data was collected over 7 nights during August 2025, using a 14” reflector telescope with full-frame camera at the remote observatory in Spain. Data was gathered using standard LRGB filters. A total of approximately 20 hours of data was finally combined to create the final image.
Location Remote hosting facility IC Astronomy in Oria, Spain (37°N 2°W)
Sessions
Frames
Equipment
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Planewave CDK14 (2563mm @ f/7.2), Optec Gemini Rotating focuser
10Micron GM2000HPS, custom pier
Moravian C3-61000 Pro (full frame), cooled to -10 ºC
Chroma 2” LRGB unmounted, Moravian filterwheel L, 7-position
Unguided
Compulab Tensor I-22, Dragonfly, Pegasus Ultimate Powerbox v2
Voyager Advanced, Viking, Mountwizzard4, Astroplanner, PixInsight 1.9.3
Processing
All processing was done in Pixsinsight unless stated otherwise. Default features were enhanced using scripts and tools from RC-Astro, SetiAstro, GraXpert, CosmicPhotons and others. Images were calibrated using 50 Darks, 50 Flats, and 50 Flat-Darks, registered and integrated using WeightedBatchPreProcessing (WBPP). The processing workflow diagram below outlines the steps taken to create the final image.
After integration using the ESD rejection algorithm with standard rejection limits, there was still a significant satellite trail visible in the luminance stack. In fact, it was so broad and distracting, that I became curious what kind of satellite trail had caused such an effect on a stack of 200(!) images. Blinking them all quickly revealed the culprit. It was a massive plane-trail, with flashing wing-lights and even visible tail fin. This was by far the most obtrusive object I’ve ever seen in my images. No wonder the rejection algorithm had difficulties eliminating its effects.
Probably the most intrusive plane trail I have ever see in any of my images. Wing-flashes, tail fins and three massive trails. The rejection algorithm was unable to fully eliminate its effects, so the frame was deleted from the stack.
Automatic stretching algorithms such as SmartStretch (Cosmic Photons) and Statistical Stretch (Seti Astro) generally do a very good job. But for stretching galaxies with all their detail, I found a manual approach with multiple GHS steps often works just a little bit better. So that approach was used for this image.
The rest of the processing followed largely a standard processing workflow as is shown below.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
