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Cosmic Challenge: Abell Galaxy Cluster 2065


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Cosmic Challenge: Abell Galaxy Cluster 2065

 

July 2022

Phil Harrington

This month's suggested aperture range:

15-inch (38cm) and larger

 

 

Target

Type

RA

DEC

Constellation

Mag

Size

AGC 2065

Galaxy cluster

15 22.7

+27 43

Corona Borealis

--

22.4'

 

 

This month, our telescopes will transport us across an incredible 1.2 billion light years (some sources quote 1.5 billion) to Abell Galaxy Cluster (AGC) 2065. More than 400 galaxies are huddled within AGC 2065, but because of that incomprehensible distance, the light from these massive collections of stars has dwindled to nothing more than the faintest whisper. Seeing even the slightest hint of AGC 2065 takes more than just aperture; it also takes supremely dark skies, a trained eye, and an accurate chart of the region.

 

Above: Summer star map showing the location of this month's Cosmic Challenge.

 

Credit: Map adapted from Star Watch by Phil Harrington

 

Above: Finder chart for this month's Cosmic Challenge.

 

Credit: Chart adapted from Cosmic Challenge by Phil Harrington
Click on the chart to open a printable PDF version in a new window

 

 

 

Like other AGC galaxy clusters, AGC 2065 was discovered on the Palomar Sky Survey photographic plates taken in the 1950s and is one of more than 2,700 such clusters published by George Abell in 1958 in a paper entitled The Distribution of Rich Clusters of Galaxies (Astrophysical Journal Supplement, 1958 vol. 3 p. 211-288). This particular cluster presents one of the most daunting challenges in Abell's list. None of the galaxies shine brighter than 16th magnitude; most are only 17th, and even 18th magnitude.

 

Burnham's Celestial Handbook describes the cluster as "one of the most remarkable of all such aggregations" in the sky. The cluster was also included in volume 5 of the classic Webb Society Deep-Sky Observer's Handbook published in 1982, but the description did not encourage observation. "Because of its staggering distance it is beyond the reach of most amateur astronomers, being undetectable in 16-inch (41cm) reflectors even under good sky conditions." Despite that dire statement, the location of AGC 2065 is plotted just west of Alpha (α) and Beta (β) Coronae Borealis on Sky Atlas 2000.0, an atlas that usually restricts its deep-sky targets to those visible through 10-inch (25cm) and smaller apertures.

 

Further, there have been several posts on CN in the past that are worth reviewing before you dive headlong into this month's challenge. I particularly recommend Alvin Huey's post from 2007 and this 2009 post by CN member tatarjj. Both include annotated images of the cluster from the Simbad Astronomical Database. Huey also authored a book 

 

AGC 2065's position so near the Northern Crown's two brightest stars makes zeroing in on it a piece of cake. Finding any evidence of its existence is something else, however. To try your luck, drop 1½° southwestward from Beta to 7th-magnitude SAO 83797. AGC 2065 is centered just 20' south of that yellow giant sun, wedged in between two 10th- and 11th-magnitude Milky Way stars.

 

Choose an eyepiece that will produce about 200x through your telescope. Sit down at the telescope, breathe, and relax! Standing and straining to see these faint targets will only lead to disappointment. Focus your attention on the 11th-magnitude field star shown on the chart, and then look just 1.4' to its east. Can you spot PGC 54876, which most agree is the easiest galaxy in the cluster to see? Using averted vision, try to catch a fleeting glimpse of its round, evenly illuminated disk. Its small size may disguise it as a star at lower magnification, but at 200x or more, its slight fuzziness will give it away its true nature.

 

 

Above: PGC 54876 (above center) is the brightest galaxy in this rendering through the author's 18-inch (46cm) reflector.

 

 

Glance another 1' to the east for an even fainter glow. Although it will probably look like a single object, this second target is a galactic pair, PGC 54881 and PGC 54883. By using averted vision through my 18-inch at 294x, I can tell that this object is about double the size of PGC 54876. Try as I might, I have never been able to resolve them as two separate systems. Others, undoubtedly observing under better sky conditions, report success.

 

PGC 54891 is also doable with patience. Its extremely faint, round glow appears just 1.2' southwest of a 14.3-magnitude star. If you manage to spot it, you might also notice a second, faint, slightly elongated speck just to its south. That's PGC 54890. PGC 54875 may also be visible, although it appears fainter than those mentioned above. Look for it 2' northeast of the 11th-magnitude star and about 1½' north of PGC 54876.

 

How many other galaxies in AGC 2065 are visible through the largest amateur telescopes? Some on-line accounts report seeing dozens. To find out for yourself, the table below lists 18 possibilities. Most do not have reliable magnitude estimates, however, so approach the listing with caution.

 

Members of AGC 2065 

(Highlighted entries are discussed above)

 

 

RA

Dec

Magnitude

Size (')

PGC 54858

15 22.1

+27 42.2

--

0.2'

PGC 54870

15 22.3

+27 42.0

18.8

0.3'x0.2'

PGC 54867

15 22.3

+27 42.1

--

0.3'

PGC 54869

15 22.3

+27 42.8

--

0.4'x0.2'

PGC 54868

15 22.3

+27 48.4

17.5

0.3'

PGC 54874

15 22.4

+27 40.9

--

0.1'

PGC 54876

15 22.4

+27 42.8

15.1

0.4'

PGC 54875

15 22.4

+27 44.3

16.9

0.3'

PGC 54884

15 22.5

+27 41.2

--

0.3'

PGC 54878

15 22.5

+27 41.9

--

0.3'x0.2'

PGC 54883

15 22.5

+27 42.4

--

0.4'

PGC 54880

15 22.5

+27 42.6

--

0.2'

PGC 54881

15 22.5

+27 42.7

--

0.4'

PGC 54891

15 22.6

+27 40.7

16.3

0.3'x0.2'

PGC 54892

15 22.6

+27 41.1

--

0.2'

PGC 54888

15 22.6

+27 41.8

--

0.3'x0.2'

PGC 54894

15 22.7

+27 37.1

--

0.2'

PGC 54890

15 22.7

+27 40.3

17.6

0.3'x0.1'

 

 

Regardless of how many of these distant galaxies you can find, be it only 1 or 18, keep in mind what you are seeing. Bob King, also known as AstroBob, captures the experience best by offering this thought: "When the light I saw left the galaxy cluster, complex cells had evolved on Earth but not a single multi-cellular organism swam about. In the time it took to get here, the tree of life sent out branches in many directions including the twig of humanity. What a privilege to be here now, over a billion years later, and catch a few photons from four ghosts in Corona Borealis."

 

For more information and observing tips on observing AGC 2065 and other Abell Galaxy Clusters, visit Huey's website, www.faintfuzzies.com. There, you will find information about his online book Observing Selected Small Galaxy Groups as well as other volumes in his deep sky observing guide series.

 

Have a favorite challenge object of your own?  I'd love to hear about it, as well as how you did with this month's test.  Contact me through my website or post to this month's discussion forum.

 

Until next month, remember that half of the fun is the thrill of the chase.  Game on!



About the Author:

Phil Harrington writes the monthly Binocular Universe column in Astronomy magazine and is the author of 9 books on astronomy.  Visit his web site at www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2022 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.

 


  • John O'Hara, warddl and Chuck99 like this


13 Comments

Photo
John O'Hara
Jul 01 2022 02:17 PM

We'll, I'll have to leave this one for the folks with the big guns.  I'd normally give it a try, but I'm on the road with only a 4" refractor.  I look forward to others' posts!

 

John

    • Jon Isaacs and PhilH like this

Stoking aperture fever ;D

    • PhilH and John O'Hara like this
Photo
JerryStellar
Jul 06 2022 08:52 AM

I could not stop reading this ! 
my C11 has no chance so reading is it for now!

j

    • PhilH and John O'Hara like this
Photo
John O'Hara
Jul 06 2022 10:34 AM

I could not stop reading this ! 
my C11 has no chance so reading is it for now!

j

You just never know.  If I had my 12.5 inch Dob with me, I might give it a go.  At best, I'd probably only see the mag. 15.1 galaxy...maybe.  From a dark site (Bortle 2 or 3) on fine night, with good vision, a good 12.5 inch scope should reveal 16 mag. stars.  So I'd say about 1 mag. brighter would be the detection limit for galaxies (depending on morphology/surface brightness, etc.).  Several years ago we were seeing mag. 16+ galaxies at Cherry Springs Dark Sky Park with a 20" Starmaster.  You just might get that 15.1 mag. galaxy with your 11 inch.  

    • PhilH and JerryStellar like this
Photo
John O'Hara
Jul 06 2022 10:35 AM

I should add that I'm talking about what I was capable of doing many years ago.  With the start of cataracts, I'm not sure how faint I can go now.  But I keep trying.

    • PhilH likes this
Photo
JerryStellar
Jul 06 2022 07:24 PM

I feel your pain…my eyes have went to crap when I turned double nickel… 55.

  I would definitely try and give it a go.. the C11 has a limited stellar magnitude of 14.7.

maybe if all things lined up perfect in the world… maybe, just maybe I could sniff out one lol.

    • PhilH and John O'Hara like this

These are my astrophotography observations of Abell 2065.  I have not tried it using visual observing, but it is nice to find a correlation to Phil Harmon's documentation.

Exposure: 3 hrs, 48 min

Location: Ridgecrest, CA

Bortle: 4

 

Keith

 

Abell 2065
 
Abell 2065 july 7, 2022
 
Abell 2065 cropped annotated

 

 

Edit: Sorry Phil "Harrington".  The brain fell through a crack there.

    • PhilH and John O'Hara like this

 

These are my astrophotography observations of Abell 2065.  I have not tried it using visual observing, but it is nice to find a correlation to Phil Harmon's documentation.

Exposure: 3 hrs, 48 min

Location: Ridgecrest, CA

Bortle: 4

 

Keith

 

Yup, that Phil Harmon sure knows what he's talking about!  lol.gif grin.gif 

    • John O'Hara and kerniew like this

I could not stop reading this ! 
my C11 has no chance so reading is it for now!

j

Not for nothing, Jerry, I spotted those galaxies through my 18" through Bortle 6 skies. You might be able to ferret out the brighter ones depending on how good your skies are. I'd certainly give them a go when a better-than-average night comes along.

    • John O'Hara likes this
Photo
Matt Lindsey
Jul 08 2022 08:03 PM

I was able to just barely detect PGC 54876, the brightest galaxy, with my 16" dob from Cherry Springs a few months ago under average transparency conditions using averted vision.   

    • PhilH and John O'Hara like this

This was a challenge object for 10” scopes at the 2016 Oregon Star Party. (Don’t know if anyone actually managed it in a scope of that size; I vaguely suspected it (e.g. “lumpy darkness”] in a 12.5”.)

Old favorite.  Here is my observation about 15 years ago.  https://www.cloudyni...alaxy-clusters/

Phil, I meant to get this one earlier, but did not.  I visited it before in Bortle 1 skies (Grandview Campground in the White Mountains) with my 20".    While I had been targeting some very dim dwarf galaxies and the like, it was my first foray into going after particularly small and faint galaxies in a more distant Abell galaxy cluster. 

 

Unfortunately, I didn't keep careful track of what I observed and only logged the ones I was certain of the ID, rather than the ones I actually saw.  So my haul was only 6, although I know I saw at least a dozen, and probably more like 18. 

 

This is one I want to revisit now that I have a system down for making finder charts for ones like this, and using it to max effect in the field, employing more magnification. For me June is a better window for this cluster, and July has been problematic with fire smoke and weather this year.

 

In the vein of preparing to reobserve, I looked at your PGC list and positions, and have prepared a portion of an SDSS-III chart for my use.  In checking Wikisky SDSS-III vs. NED and Hyperleda I have found some potential corrections to your chart as follows. 

  • PGC 54868 (MCG+05-36-018) is actually further east.  Using the g and r mags I put it at ~16.3 V mag.  
  • The galaxy shown as PGC 54868 is a good target, but is 2MASX J15221649+2748261.  It is odd that it was not included in earlier surveys, since its g and r mags work out to ~16.0 V mag, and it is of good size.
  • PGC 54858 (MCG+05-36-016) is actually further south than the galaxy shown.  I calculate it as 16.5 V mag. 
  • The galaxy shown as PGC 54858 is actually 2MASX J15220337+2742100 from what I can tell.  Extrapolating from its 2MASX J magnitude, it is likely close to 16.9 V mag.   
  • PGC 54892 is southeast of the group of three galaxies shown.  
  • The one shown as PGC 54892 is PGC 1815146, roughly 17.3 V mag.

The next set plays musical chairs...with one shown object losing its seat.

  • PGC 54881 is actually in the position shown as PGC 54878.  
  • PGC 54878 is the next galaxy to the west of the real 54881.  It works out to ~17.4 V mag.
  • PGC 54888 (MCG+05-36-022) is where PGC 54881 is shown.
  • The object shown as PGC 54888 corresponds to a pair of stars.  No galaxy here. 


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