Date: Sept 3, 2025

Cosgrove’s Cosmos Catalog ➤#0147

By the time this image was taken, the Supernova had diminished quite a bit and it was a challenge to pull it out of the glare of the bright core. (click for full res image via Astrobin.com)

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About the Target

Overview

NGC 7331 is a prominent spiral galaxy located roughly 40 million light-years away in the constellation Pegasus.

Friedrich Wilhelm Herschel 1738-1822 (from Wikipedia)

It was discovered by astronomer William Herschel in 1784 and is sometimes called a “twin” of the Milky Way due to its similar size and structure.

.NGC 7331 is an unbarred spiral and is tilted about 75° to our line of sight, which exposes its spiral arms and dark dust lanes. The galaxy’s central bulge is pronounced and contains a supermassive black hole, and with an apparent magnitude of around 10.4, it ranks as one of the brightest galaxies visible to amateur telescopes.

Just a few arcminutes away in the sky, a collection of four smaller, faint galaxies surrounds NGC 7331. Collectively, these neighbors are nicknamed the “Deer Lick Group.” While some sources describe this moniker as an analogy, NGC 7331 is like a “salt lick” attracting a handful of “deer” (the companion galaxies). In some astronomy circles, those dim companion galaxies have even been jokingly called “the Fleas” next to the big galaxy. However, it would seem that this name originated from amateur astronomer Tom Lorenzin in the 1980s, who observed the galaxy cluster from the Deer Lick Gap Overlook in the North Carolina mountains. This was actually a tribute to the famous observing location, not a description of the galaxies' appearance.

The Deer Lick grouping includes galaxies NGC 7335, 7336, 7337, and 7340, which appear close to NGC 7331 in visual maps.

However, this is only a chance alignment – NGC 7331 lies approximately 40 million light-years from us, whereas the four “deer” are about 290–350 million light-years distant.

So, NGC 7331 is in the foreground, and those smaller galaxies are far in the background, so they are not physically related or bound together by gravity. This line-of-sight coincidence nevertheless provides a striking view: the big, nearer galaxy in the foreground, contrasted against the tiny background galaxies, illustrates the immense depth of field in our universe.

Historically, NGC 7331 was overlooked by Charles Messier’s famous catalog. Still, it later gained recognition in amateur observing guides (it’s listed as Caldwell 30), and it continues to intrigue observers, especially when framed with its “Deer Lick” companions.

Supernova SN2025rbs in NGC 7331

In July 2025, galaxy NGC 7331 became host to a new supernova designated SN 2025rbs.

This stellar explosion was first detected on 14 July 2025 by the Gravitational-wave Optical Transient Observer (GOTO), an automated network of wide-field robotic telescopes that scans the sky for transient events. Astronomers quickly obtained follow-up observations and determined that SN2025rbs is a Type Ia supernova, identified by its characteristic spectral features.

A Type Ia supernova is the catastrophic thermonuclear explosion of a white dwarf star in a close binary system. In such systems, the white dwarf gradually steals matter from its companion star; if the white dwarf’s mass approaches the Chandrasekhar limit (about 1.4 times the Sun’s mass), it becomes unstable and detonates in a runaway fusion reaction. This results in a brilliant burst with no hydrogen in its spectrum – a key signature that distinguishes Type Ia supernovae from other types. The classification of SN2025rbs as Type Ia was confirmed by comparing its spectrum to known supernova templates, which showed it closely matched a normal Type Ia event just a couple of weeks before peak brightness. In essence, what erupted in NGC 7331 was a white dwarf that had reached the tipping point and obliterated itself, briefly outshining its entire host galaxy.

SN2025rbs appeared very near the luminous core of NGC 7331, practically in the galaxy’s inner region, which makes it a bit of a challenge to spot against the bright central glow. Despite its location against the galaxy’s nucleus, the supernova brightened significantly in the weeks after discovery.

It was initially around magnitude 17 at discovery, but it surged to about magnitude 14 at its peak – meaning it became roughly 25 times brighter than when first spotted. (For context, lower magnitudes denote brighter objects, so this peak made SN2025rbs visible in moderate amateur telescopes.)

In fact, it was among the most luminous supernovae observed in 2025!

Even by the end of August 2025, several weeks after maximum light, SN2025rbs was still holding around magnitude 14.4, slowly fading but remaining visible. This relatively slow fade gave astronomers and enthusiasts ample time to monitor and photograph the supernova over the summer, which is why I was able to image it this late after its discovery.

Interestingly, SN2025rbs is the fourth supernova on record in NGC 7331.

Previous supernovae in this galaxy were observed in 1959, 2013, and 2014, highlighting that large spiral galaxies like NGC 7331 occasionally produce these stellar explosions. Notably, the 2014 event (SN 2014C) in NGC 7331 drew scientific attention for its unusual evolution – it started as one type of supernova (Type Ib) but over the course of a year transformed into a hydrogen-rich Type IIn as it interacted with surrounding material. While SN2025rbs is a more “standard” Type Ia, its occurrence provides both a stunning visual in an already picturesque galaxy and valuable data for researchers.

Overall, the sight of NGC 7331 flanked by the Deer Lick Group and highlighted by the brilliant flare of SN2025rbs offers a remarkable scene. For newcomers to astronomy, it showcases a grand spiral galaxy not unlike our own Milky Way, and for seasoned observers, it’s an opportunity to witness a fresh supernova amplifying the view of a well-known deep-sky object.

Annotated Image

Image created with Pixinsight’s ImageSolver and AnnotateImage scripts.

Location in the Sky

Findershart created with Pixinsight’s ImageSolver and FinderChart scripts.

About the Project

During the last week of August, we had some “iffy” nights. These are nights when the weather apps suggested that there might be periods of clear skies, but also indicated a real possibility of cloud formations moving in.

However, with the observatory now operational, I felt there was little downside to capturing images on these nights. Set up and shut down are not he major tasks they used to be, so it was not such a big deal to start capturing on one of these nights and see where things went.

In fact, the good news is that I am typically not in the observatory very much!

First, I set up the scopes remotely from my Astro Man-Cave.
- I program the NINA sequence
- I turn the power on to the scopes themselves via a remote relay
- Then I connect each of the scope devices within NINA.
Then I go out to the observatory for a few minutes:
- I unlatch the roof and open it.
- I take the caps off all of the scopes.
Then it’s back to the Man Cave
- I watch things over a security camera
- I fire off the NINA sequences
- NINA takes it from there.

I slept for most of these nights (yes - slept! I love it when a plan comes together!)

In the past week, I have been shooting a narrowband series of the Cave Nebula with my Sharpstar SCA260. I already had some good data for the project, but I planned to collect more.

But an old astro friend of mine, Glenn, had shown me some images of the Supernova in NGC 7331 that a member of our local astronomy club shared. He prodded and suggested I give it a try.

So I thought - why not!

I could quickly program a NINA sequence to do this, and I could possibly take an hour or so to capture the data, then return to my original target.

Easy-peasy.

Well - except for that sleep part. I set an alarm to swap out targets (yes, I know I could have automated this within NINA as well, but this is a quick and dirty thing on the fly). The alarm went off and — I was lazy and decided to let it run all night whilst I went back to sleep!

S0 - it went all night…

I ended up with almost 5 hours of integration. Even with this short an integration time, I was happy with the detail I was able to capture on the target. While the Supernova was a little hard to see, being embedded in the bright haze of the core, the detail in NGC 7331 was pretty satisfying!

The “Flies”, the four “companion galaxies,” show up quite well. I find it fascinating that NGC 7331 is a foreground object at a paltry 40 Million Light-years away, while the “companions” are about 350 million light-years away!

I expected to see no detail in these galaxies due to their size and distance, but there is some detail on a couple of them.

NGC 3773 is a barred spiral with a classification SB(rs)b, which is estimated to be 300 million light-years away. It has the most structure and detail of the bunch.

NGC 7335 is a Spiral galaxy with a bright core that is classified as S0-Aa, and is estimated to be 303 million light-years away. Again - you can just start to make out details of its spiral form.

NGC 7336 is an Intermediate Spiral galaxy with a classification SBc, and is located approximately 294 million light-years away. You can see a hint of its spiral form and maybe a distortion towards the bottom.

NGC 7340 is an elliptical galaxy with a bright core, with a classification of E3. It is estimated to be 290 5to 332 million light-years away.

Data Capture

Data was captured on the night of August 30.

I decided on doing an LRGB sequence of 90-second exposures with the camera cooler aim set to -10 degrees C. Since I don’t have a rotator on the SCA260, I centered NGC 7331 and the Deer Lick group in the middle of the field.

I normally set the sequence to use focus offsets and then rotate through the filters to get separate L, R, G, & B subs for each cycle. However, this time I set it up to capture two Lum subs and then one each for R, G & B.

I thought there was an offhand chance that I might do a B&W image here, so I decided to stack the deck with lum subs.

Data collection happened without any errors, and I slept through most of it! (Yay!)

Image Processing

Normally, I would use a Starless processing workflow to deal with this image. However, I was a little concerned that it might cause an issue with the SN, and I wanted to simplify the process, so I opted for an old-fashioned 'leave-the-stars-in’ methodology.

As you might expect, I processed the L image to enhance detail and sharpness, and the RGB image to increase color and reduce noise, and then combined them at the end.

I quickly realized that the Master Images did not seem to show the supernova at all! It was lost in the bright glow of the nucleus of this galaxy.

If I looked at a single blue filter 90-second sub, I could clearly see the core of the galaxy as well as the SN:

A zoomed in portion of a single blue filter subframe shows the nucleus as well as the Supernova.

If I look at a Lum subframes, it gets harder to see:

In an Luminance Subframe, the SN is starting to get lost in the glow of the core.

Why is this? Well, the cut of the blue filter is nominally 100 nanometers wide, while the L filter has a cut of about 300 nanometers. It has a larger spectral window, which means it just captures more photons.

So if I processed my image the way I normally would, there would be no SN to see. If I processed the image so the SN was visible, the rest of the galaxy would be suppressed.

I ended up creating a gradient mask using the GAME script. This covered the core of the galaxy and allowed me to segment the processing into “core” and “not-core” processing by using this mask and its inverse.

I tried to strike a happy medium between a great view of the galaxy while still being able to discern the SN.

In my FInal image, you can still see the SN while the core does brighten as it should

But I did go back and processed a B&W version of the image where I darkened things so that the SN was more evident. I biased the processing a bit towards the SN rather than the whole scene.

Here is a zoomed in version:

Note: A detailed Image Processing walkthrough can be found at the end of this post!

Results

I'm reasonably happy with the final result!

I only had less than 5 hours of integration, but the image of the galaxy came out nicely, and I was still able to see the Supernova. Not a bad balance.

What would I do differently next time? I think I would do better with shorter sub exposures - maybe 30 seconds.

But more importantly, I think I would have done much better if I had captured the SN earlier in its life cycle, when it was at its brightest. Then there would be no problem showing it!

More Info - NGC 7331 Group

🔭 Target Details

https://en.wikipedia.org/wiki/NGC_7331 — Concise overview: type, distance, discovery, and why it’s often compared to the Milky Way.

https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-caldwell-catalog/caldwell-30/ — Hubble “Caldwell 30” page with object data, context, and observing notes.

https://www.spitzer.caltech.edu/news/ssc2004-12-seeing-double-spitzer-captures-our-galaxys-twin — Spitzer release explaining the galaxy’s IR structure (bulge, star-forming ring, arms) as a Milky Way analog.

📜 History & Nomenclature

https://freestarcharts.com/ngc-7331 — Discovery date, basic facts, and finder charts for visual observers.

https://www.fortlewis.edu/observatory/image_detail.asp?ID=267 — Short historical note (missed by Messier) and “Deer Lick Group” context.

🧠 Science & Research

https://esahubble.org/images/potw1805a/ — ESA/Hubble image + caption discussing structure and similarities/differences with the Milky Way.

https://noirlab.edu/public/images/iotw2451a/ — NOIRLab “Image of the Week” highlighting structural details (inclination, bulge/disk behavior).

https://arxiv.org/abs/astro-ph/9602142 — Research paper reporting a counter-rotating bulge component in NGC 7331 (historically notable result).

🖼️ Images & Visualizations

https://apod.nasa.gov/apod/ap230914.html — APOD: deep portrait “NGC 7331 and Beyond,” showing the foreground galaxy and background “Deer Lick” companions.

https://www.spitzer.caltech.edu/image/ssc2004-12a-morphology-of-our-galaxys-twin — Spitzer multi-band visualization separating bulge, ring, and arms.

https://science.nasa.gov/gallery/hubbles-caldwell-catalog/ — Hubble Caldwell gallery entry with imagery and the location of SN 2014C marked.

🧭 Observing & Finder

https://www.constellation-guide.com/ngc-7331/ — Object profile with location, dimensions, and notes on the “fleas” (background companions).

https://www.jwinman.com/starcharts/NGC%207331%20chart.htm — Printable finder/star chart centered on NGC 7331.

https://skyandtelescope.org/online-gallery/deer-lick-galaxy-group-ngc-7331/ — Imaging gallery entry with field context explaining why the “Deer Lick Group” is a line-of-sight grouping.

More Info - SN 2025rbs

📡 Discovery & Classification

https://goto-observatory.org/bright-supernova-2025rbs-discovered-by-goto/ — GOTO’s official discovery write-up and early details submitted to TNS.

https://ui.adsabs.harvard.edu/abs/2025TNSAN.213….1O/abstract — TNS AstroNote abstract covering discovery/coordinates and host context.

https://www.narit.or.th/en/AstronomyNews-20250731-SN2025rbs — NARIT release with follow-up images and an accessible Type Ia summary.

🧠 Scientific Context

https://nustar.caltech.edu/news/nustar250801 — NuSTAR’s rapid X-ray follow-up; why nearby Type Ia events like SN 2025rbs are valuable.

https://ui.adsabs.harvard.edu/abs/2025ATel17303….1G/abstract — Astronomer’s Telegram abstract on early NuSTAR observations and timing.

https://science.nasa.gov/mission/roman-space-telescope/type-ia-supernovae/ — Background explainer on Type Ia supernova physics and use as standard candles.

🖼️ Images

https://www.virtualtelescope.eu/2025/07/17/supernova-sn-2025rbs-in-the-ngc-7331-spiral-galaxy-an-image-16-july-2025/ — Early image (16 Jul 2025) showing the supernova near the bright core.

https://www.virtualtelescope.eu/2025/08/01/supernova-sn-2025rbs-in-the-ngc-7331-spiral-galaxy-an-image-1-aug-2025/ — Follow-up image near maximum light with magnitude estimate.

https://apod.nasa.gov/apod/ap250731.html — APOD (31 Jul 2025) featuring SN 2025rbs in context within NGC 7331.

🔭 Observing & Light Curves

https://www.rochesterastronomy.org/sn2025/sn2025rbs.html — Rochester Astronomy page aggregating images/links and brightness notes for SN 2025rbs.

https://www.rochesterastronomy.org/supernova.html — “Latest Supernovae” hub tracking current magnitudes and discoveries (2025 listings include SN 2025rbs).

https://app.astrobin.com/i/xs15vv — Example high-quality amateur image page with acquisition details and framing (good for visual comparison).

Capture Details

Lights

Taken on the night of Aug 30, 2025.
Number of frames is after bad or questionable frames were culled.
80 x 90 seconds, bin 1x1 @ -10C, gain 0, ZWO 36mm diameter Lum Filter
38 x 90 seconds, bin 1x1 @ -10C, gain 0, ZWO 36mm diameter Red Filter
35 x 90 seconds, bin 1x1 @ -10C, gain 0, ZWO 36mm diameter Green Filter
35 x 90 seconds, bin 1x1 @ -10C, gain 0, ZWO 36mm diameter Blue Filter
Total of 4 hours 42 minutes.

Cal Frames

30 Darks at 90 seconds, bin 1x1, -10C, gain 0
30 Dark Flats at each Flat exposure times, bin 1x1, -10C, gain 100
15 Lum Flats
15 Red Flats
15 Green Flats
15 Blue Flats

Capture Hardware:

Click below to see the Telescope Platform version used for this image

Featured

The 4th Pier: The Sharpstar SCA260 V2 Platform Ver 1.0

Miscellaneous, SCA260V2

Apr 21, 2025

The 4th Pier: The Sharpstar SCA260 V2 Platform Ver 1.0

Miscellaneous, SCA260V2

Apr 21, 2025

This post documents the setup and configuration of my New ‘Galaxy” scope, the Sharpstar SCA260 V2.

Image Processing Detail (Note: This is all mostly based on Pixinsight with image polishing done in Photoshop)

1. Blink Analysis

Lum Subs:

15 removed for clouds

Red Subs:

5 frames removed for clouds

Green Subs:

9 removed for clouds

Blue Subs:

11 fames removed for clouds

All Flats and Darks:

All looked good!

2. Assess all captures SubframeSelector

Lum Filter:

14 frames removed

Red Filter:

5 images removed

Green Filter:

4 frames removed

Blue Filter:

3 frames removed

Summary:

A total of 62 subs were removed as not being top quality
The total time of the removed frames was 1.55 hours lost!

3. WBPP Script V 2.8.9

Load all files
Dark exp tolerance set to zero
Light exp tolerance set to zero
Pedestal auto for all frames
CC auto for all groups
Select max quality
Ref image set to auto
Selected the target folder
Executed in 2:11 with no errors

4. Import Master image, Rename, Create Color RGB Image

Import master images and rename
Use ChannelCombination to create the initial RGB image.

5. Remove Gradients

Sampling pattern chosen to avoid galaxies
DBE was used with subtraction

6. Create and Process the Linear RGB Color Image

Apply BXT on the color image with “Correct Only”
Set up the SPCC panel and run it on the image. In this case, we will use the 571 device curve, choose the ZWO R, G, & B filters, and choose an area of the image to represent the reference background.
Run PFSImage: X = 3.49 Y = 3.36. Not sure, I believe these are the diffraction spikes that might influence things.
Apply BXT with full correction. See panel-snap below for values used. These were selected after interactive testing.
Run NXT V3 - see panel snap below for final parameters used.
Note: Some images below will be shown full screen, while others will be shown zoomed into a likey crop positon so you can see small changes beter.

After SPCC - Zoomed into likely crop region, (click to enlarge)

Before BXT

After BXT Correct Only

Aftere SPCC

After Full BXT

After NXT V3

RGB Image Before BXT, After BXT Correct Only, After SPCC, After BXT Full Correction, After NXT V3

7. Process the Linear Lum Image

Apply BXT on the Lum image with “Correct Only”
Run PFSImage: X = 3.76 Y = 3.64. Not sure I believe this as the diffraction spikes might influence things.
Apply BXT with full correction. See panel-snap for values used. These were selected after interactive testing.
Run NXT V3 - see panel snap below for final parameters used.
Normally, at this point, I would go starless. But I am a little concerned with impacting the images of the supernova itself, so I have decided to go pretty much old school on this - I will not be using a starless workflow.

Before BXT

After BXT Fix Only

After BXT Full

After NXT V3

Before BXT, After BXT Fix Only, After Full BXT, After NXT V3

8. Take Images Nonlinear

For the Lum image, use the STF->HT method.
For the RGB image, use the STF-HT method.

9. Process the Nonlinear Lum image

Use CT to darken the background sky and slightly darken the galaxy
Create a mask using GAME to cover just the core of the NGC 7331 - we will call it the CoreMask.
Apply the CoreMask and run HDRMT with levels = 5 as shown in the screen snap below.
With the CoreMask still in place, use CT to adjust the core further.
Invert the CoreMask and use CT to adjust the rest of the scene.
Do an MLT sharpening (see MLT Panel screensnap to see params used) with the CoreMask in place - trying to enhane the core and the SN.
Do a final CT with no Mask

10. Process the Nonlinear RGB Image

Apply a global CT adjust dial in the intensity signal and a color saturation boost.
Apply the CoreMask, and do another CT.
Invert the CoreMask and do another CT, adjusting the rest of the image.
With the Inverted CoreMask, apply LHE with a radius of 134, max contrast of 2.0, an amount of 0.2, and an 8-bit histogram. This will enhance the contrast of larger-scale features.
I now want to enhance the blue of the outer galaxy and the warmth of the inner galaxy, so I set up a color saturation curve in the ColorSaturaton tool and applied it with an inverse CoreMask.
Use ChannelCombination in CIE Mode, with only the Luminance channel selected to add the Lum Image into the RGB image.
I am anticipating that I will do a tight crop around the main galaxy and Deer Lick group - with this “magnification,” I am concerned that the star image sizes will look bad. Although I did not use a starless workflow, I will still use the ReduceStars Script to adjust things. That will need a starless image, so create one with SXT.
Now run the StarReduction Script. I enabled the Small Star Protection, and after some experimentation, I also used the Moderate setting for best results.
One thing I did not like about what Star Reduction did was that I found some bright color rings around red stars. To tone this back a bit, I created a color saturation curve for the ColorSaturation tool that reduced the saturation on bright red.
I did not want the red-ring fix to work on the body of the galaxy, so I created a GalaxyMask with GAME that covered the body of the Galaxy.
With the Inverse GalaxyMask applied, I ran the ColorSaturation Process.
I’m pretty happy with the image now, and I can see the SN just fine. But the problem is that the core looks unnatural because it is not as bright as it should be. So, I applied the CoreMask once again, brightening it as much as I could while still allowing the SN to be seen.