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Cosmic Challenge: Hickson Compact Galaxy Group 50
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Cosmic
Challenge:
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This month's suggested aperture range: 15-inch (38-cm) and larger telescopes |
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Target |
Type |
RA |
DEC |
Constellation |
Magnitude |
Size |
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HCG 50 |
Galaxy group |
11h 17.1m |
+54° 55.3’ |
Ursa Major |
varies |
<1' |
Observing compact galaxy groups from Paul Hickson's 1982 study is an interesting challenge for owners of the largest backyard telescopes. Most are at the edge of detection, even from dark sites, and so offer great tests of our observing skills as well as the quality of our instruments' optics.
Last month, I challenged you to observe Hickson Compact Group 44 (HCG 44). Many of you posted your success stories in that column’s discussion forum, which were great to read. This month, we are back in search of even bigger game.
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Above: Evening star map. Credit: Map adapted from Star Watch by Phil Harrington |
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Below: Finder chart for
this month's Cosmic Challenge. |
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I especially enjoy the hunt for number 50 in Hickson's list of 100. Hickson Compact Galaxy Group 50 (HCG 50) is comprised of five dismally faint galaxies crammed into an incredibly tight 45". The table below lists details of each.
Members of HCG 50
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Target |
RA |
DEC |
Magnitude* |
Size* |
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HCG 50A (PGC 34447) |
11 17.1 |
+54 55.0 |
18.7 |
0.2'x0.2' |
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HCG 50B (PGC 34452) |
11 17.1 |
+54 55.0 |
18.9 |
0.3'x0.1' |
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HCG |
11 17.1 |
+54 55.3 |
19.6 |
0.2' |
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HCG 50D (PGC 34448) |
11 17.1 |
+54 55.4 |
19.5 |
0.3'x0.1' |
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HCG 50E (PGC 34453) |
11 17.1 |
+54 55.2 |
20.0 |
0.2'x0.1' |
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* Note: magnitude and size values from Megastar v5 |
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Why is this my favorite Hickson challenge? Largely for the company it keeps. HCG 50 is just 1/2° east-southeast of M97, the famous Owl Nebula, which is fascinating in its own right through large apertures. I rarely head out on a spring night when I don't at least stop by the pay the Owl a quick visit. If the sky is clear enough, I'll often continue on to HCG 50. If I can make out even the faintest hint of it, then I know the night is, in fact, quite special.
To spot HCG 50, begin by placing M97 in the center of a medium-power eyepiece; I tend to favor a 12-mm eyepiece (171x) in my 18-inch. Moving the Owl off to the northwestern edge of the field brings a distinctive asterism of four stars in the shape of the Hercules keystone into view. HCG 50 is just 9' east of the keystone's center. For scale, each side of the keystone measures between 3' and 4' in length.
From my suburban backyard observatory, the best I can report of this challenge is seeing a slightly elongated smudge in the right spot that is just barely above the background at 171x and 206x. I have never been able to resolve the individual galaxies, even at 300x or more. I believe the smudge I saw was the combination of HCG 50A and 50B, the two brightest members of the group. HCG 50C and 50D are both fainter and evaded my quest, as did the dimmest, HCG 50E.
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Above: Digitized sketch of HCG 50 through the author's 18-inch (46-cm) reflector.
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Above: HCG 50 (and the Owl Nebula) taken through the author's Celestron Origin Home Observatory astrograph. Click here for a full size image and exposure details on the author's Astrobin page. |
The fact that I can see any evidence of the group's existence through a 5th-magnitude sky attests to the fact that we should not be put off by faint magnitude values. Notice how the magnitudes for each galaxy here is its "B" or "blue magnitude." That is often how galaxies are listed, but it can be deceiving. In general, so-called blue magnitudes are biased toward lower values than visual magnitudes. A target with a blue magnitude of, say, 18 may appear closer to magnitude 16 visually.
Here’s something to ponder. These galaxies are estimated to be between 1.5 and 2 billion light years away. The light I recorded from my backyard left those galaxies when life on Earth consisted primarily of single-celled organisms, with the most significant development being the emergence of "eukaryotes" - cells with nuclei, which eventually led to the evolution of all multicellular life. Our planet was covered by a vast ocean and had no continents at all. For the past 1.5 to 2 billion years, that light has been screaming along at an incredible 186,000 miles (300,000 kilometers) every second – 5.88 trillion miles (9.46 trillion kilometers) every year -- just to reach my telescope. It’s numbers and realizations like those that have kept me captivated by this science and hobby for almost 60 years.
So, how did you make out with this month's challenge? I'd enjoy reading of your successes and attempts. Be sure to post your experiences in this month's discussion forum.
And do you have a favorite challenge object that you'd like to share with the rest of us? Post your suggestions in this month's discussion forum as well, and I'll try to feature them in future installments.
Until next month, remember that half of the fun is the thrill of the chase. Game on!
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About
the Author: |
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Phil Harrington's Cosmic Challenge is copyright 2025 by Philip S. Harrington. All rights reserved. No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder. |
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- John O'Hara likes this
9 Comments
Hello, wow! The faintest and most difficult of the Hickson groups of galaxies. If the aperture range is in the 15" scope's or above, will a 12" or 14" scope be able to discern even the faintest hint of this group under really dark skies at high power?, Sense a 15" scope only has 10% more light gathering ability then a 14", and 7% better resolving power, I would think so, but this group is very, very, very difficult in even the biggest of amateur telescopes. I have a 14" scope and various other capable scopes, so that is why I am asking...thanks, and clear skies!
There’s only one way to find out! Try and report back.
I'll have to give Hickson 50 a go the next time I'm at Cherry Springs and have access to one of the large Dobs belonging to observing buddies.
https://www.reinervo.../hickson_e.html
It's worth noting that HCG 50A/B (the brightest in the group) is just 20" northeast of a brighter 16th-magnitude star. You'll need to easily see this star to be able to glimpse HCG 50A, so it's a good check on whether the galaxy might be visible. If fact, even when I hold this star steadily in my 24", HCG 50A is still difficult to glimpse as it's only V = 17.2. It's missing from Phil's sketch (and description), but the star in question is at the upper left edge of HCG 50 in the photographs that accompany the article .
Thanks, Steve. Yes, you are correct. Odd that I didn't see that star when I made the sketch. Unless it was part of the blended image.
Gave this a try last night with a C14 imaging at f/11 and a 16" SCT visually. The northern half of my sky is the brightest adding to the difficulty. Visually I was unable to see any of the galaxies or the 16th magnitude star Steve notes.
A 50 minute exposure barely revealed the galaxies in the red channel (the blue and green channels were swamped by light pollution). I had used the f/11 focus to give some plate scale but I may try again at f/3.5.
A true challenge for my scopes and aged eyeballs!
I finally had a good night of viewing, so I set my N.I.N.A sequence to take images all night. I like being able to say that at 1.5 to 2 Billion light years away, that this is truly fossil light and I just so happened to have been observing that night and captured that ancient light. Good target. Thanks Phil. In my gallery you can also see M 97 with HCG 50 off to the center left.
I just received an uncooled monochrome guide camera so I tried imaging with it on HCG 50 using my C14 at f/3.8. I was pleased to see some smudges appearing in the right places on the 30 second unguided subs. Here's the dark-subtracted stacked image of 60 subs with no additional processing; north is up. This is a much better result than I got using an OSC camera at f/11.
I once observed it through Rock Mallin's Meade 16" SC using the then new Mallincam Hyper (25 odd years ago).
He had just finished his first batch of them, and a few of us went to a dark site on a glorious May day in Eastern Ontario, the day's high had been over 70 F, the night was clear with steady skies.
He and others who bought the new cameras first started on familiar objects like M51, which came out stunning us, it was like pictures you see in astronomy mags, with tremendous detail. Experienced observers (one who was a professional astronomer, working in an observatory that housed a 63 " telescope) said that it was like the telescope was performing like it was 5 times it's aperture.
After viewing a few familiar objects, Rock decided to try Hickson 50, after a bit of hunting, he got it!. All 5 galaxies were easily visible. We were amazed.
Not to be outdone, Denis Legault (we call him the Human GoTo) guided his 14" totally manual Dob to it, and after about 1 minute, it popped up clearly in his Mallincam.
Finally, as a challenge, Simon (last name forgotten, sorry), tried to get it using his 8" Meade with his Mallincam, after about 5 minutes, he finally found it, you could faintly see the 4 brightest galaxies, then occasionally, after a screen refresh, the 5th one would pop into view. That confirmed the 5x increase of aperture using the Mallincam, as one observer said that he had had a chance to use a 36" Obsession at a star party, he said that he could visually see the 5 galaxies with averted vision on a very clear night with great seeing.