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Cosmic Challenge: Abell Galaxy Cluster 373


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Cosmic Challenge: Abell Galaxy Cluster 373

 

December 2021

Phil Harrington

This month's suggested aperture range:

6- to 9¼-inch (15-23.5 cm) telescopes

 

 

 

Target

Type

RA

DEC

Constellation

Magnitude

Size

AGCS 373

Galaxy cluster

03h 38.5m

-35° 27.0'

Fornax

--

180'

 

Nestled in the southeast corner of the dim late-fall/early-winter constellation Fornax, adjacent to the distinctive triangle formed by 6th-magnitude Chi-1 (χ-1), Chi-2 (χ-2), and Chi-3 (χ-3) Fornacis, is an attractive cluster of galaxies known as Abell Galaxy Cluster - Southern Supplement (AGCS) 373.

 

 

Above: Late evening 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

 

 

In addition to his research that led to the discovery of more than 80 new planetary nebulae in the 1950s, American astronomer George O. Abell also examined the overall structure of the universe.  He did so by studying and cataloging 2,712 galaxy clusters that had been captured on the then-new National Geographic Society-Palomar Observatory Sky Survey taken with the 48-inch Samuel Oschin Schmidt camera at Palomar Observatory.  In 1958, he published the results of his study in a paper entitled "The Distribution of Rich Clusters of Galaxies" in the Astrophysical Journal Supplement (vol. 3, p.211).  Although Abell died in 1983, his catalog was expanded in 1989 by Harold Corwin and Ronald Olowin with the publication of their article "A Catalog of Rich Clusters of Galaxies," again in the Astrophysical Journal Supplement (vol. 70, p. 1-138).  The Corwin/Olowin addendum to Abells original catalog encompasses a total of 4,073 rich galaxy clusters.

 

Also known informally as the Fornax Galaxy Cluster, AGCS 373 lies nearby as galaxy clusters go, at an estimated distance of 62 million light-years.  At least 18 of its members are within range of 6- to 9¼-inch telescopes.

 

Let's start with two of the most interesting.  In 1966, American astronomer Halton Arp published his monumental Atlas of Peculiar Galaxies, a photographic survey of oddball galaxies that he made with the 200-inch Hale reflecting telescope and the 48-inch Schmidt telescope at Palomar between 1961 and 1966.  The Arp catalog's 338 entries comprise a fascinating collection of interacting and merging galaxies.  Most of the Arps are in the realm of large and giant backyard scopes, although a dozen entries involve Messier objects. [Those include M32 (Arp 168), M49 (Arp 134), M51 (Arp 85), M60 (Arp 116), M65 (Arp 317), M66 (Arp 16 and Arp 317), M77 (Arp 37), M82 (Arp 337), M87 (Arp 152), M90 (Arp 76), and M101 (Arp 26).]

 

Arp 154 involves two of the galaxies within the Fornax cluster.  NGC 1316, at 9th magnitude the brightest galaxy in the bunch, is set in the group's western suburbs.  Deep photographs reveal that NGC 1316 contains many dust clouds and is surrounded by a complex envelope of faint material, several loops of which appear to engulf a smaller galaxy, NGC 1317, 6' to the north.  Astronomers consider this to be a case of galactic cannibalism, with larger NGC 1316 devouring its smaller companion.  The merger is further signaled by strong radio emissions being telegraphed from the scene. 

 

In my 8-inch reflector, NGC 1316 appears as a bright, slightly oval disk with a distinctly brighter nucleus.  NGC 1317, about 11th magnitude and 2' across, is visible in a 6-inch scope, although averted vision may be needed to pick it out.  Try about 150x for the best view.

 

With NGC 1317 centered in your field, turn off your telescope drive and wait five minutes.  The Earth will turn your view eastward to NGC 1341, a challenging 12th-magnitude barred spiral.  I could only see it fleetingly with my 8-inch reflector from a dark site on the south shore of Long Island, New York.  Its featureless disk, only 1½' long, is just north of a faint star.

 

There is another barred spiral, NGC 1326, about halfway between NGC 1316 and Chi-1.  In the 8-inch, it appeared as an 11th-magnitude oval smudge visually measuring about 2' long and half as wide.  It also has a stellar nucleus centered within.

 

The heart of the Fornax cluster lies at right ascension 03h 38.5m, declination -35° 27.0', halfway between the Chi Fornacis triangle to the west and Sigma (σ) Eridani to the east.  A telescope with a 1° field aimed toward this position will embrace eight galaxies brighter than 14th magnitude, with 10th-magnitude elliptical NGC 1399 lying dead center (shown below).  This galaxy, set 15' south of a 7th-magnitude field star, appears as a perfectly round glow 2' in diameter with a brighter nucleus.

Above: A portion of the Fornax Galaxy Cluster through the author's 8-inch (20cm) f/7 reflector.  NGC 1399 is the bright galaxy to the right (east) of center.

Below: This VLT Survey Telescope image shows the central part of the Fornax Galaxy Cluster in great detail. At the upper left is the elegant barred-spiral galaxy NGC 1365 and to the right the big elliptical NGC 1399.

Credit: ESO. Acknowledgement: Aniello Grado and Luca Limatola

 

NGC 1404, another 10th-magnitude elliptical, is just 10' south and slightly east of NGC 1399.  I found it slightly oval with its long axis stretching 2'.  Like many of the galaxies in this cluster, NGC 1404 has a brighter nucleus.  Another 20' west-southwest of NGC 1399 lies NGC 1387.  I was surprised at how bright this spiral appeared in my 8-inch, considering it is listed as magnitude 10.8.

 

NGC 1389 is 14' south and a bit east of NGC 1387, just over the border into Eridanus.  Averted vision is a must for any scope smaller than 10 inches.  Most references label this 2'-long elliptical as 12th magnitude, but I estimate it to be a half magnitude fainter.  Somewhat brighter and larger is the elliptical NGC 1386, found about 15' south-southwest of NGC 1389 and set a bit deeper into Eridanus.  At 120x, I saw its brighter nucleus.

 

Moving back to NGC 1387, you can sweep 14' north-northwest to NGC 1381, a faint, 12th-magnitude, cigar-shaped elliptical 2' long.  About the same distance west-northwest of NGC 1387 is another 12th-magnitude galaxy, NGC 1379.  It appears as a circular glow about 1 ' across.

 

NGC 1374 measures just 1' in diameter, but should be visible in a good 4-inch scope.  Can you see NGC 1375 located just 2' to its south?  It's a magnitude fainter, so a 6-inch might be required.  A third, fainter smudge is an equal distance to the north of NGC 1374.  That's NGC 1373, a tough target in a 6-inch.

 

A 4-inch, however, should show the long, thin disk of NGC 1380 to the northeast of the NGC 1374 trio.  Because of its distinctive lenticular shape, this 10th-magnitude galaxy is an intriguing target for astrophotographers.

 

Another object with a pronounced shape is the barred spiral NGC 1365, which, at 10th magnitude, is the third brightest member of the Fornax cluster.  Visually it appears as an oval nebulous patch that grows steadily brighter toward its center.  Photographically it is one of the most impressive examples of a barred spiral south of the celestial equator.  It has long curving arms that extend north and south from a pronounced central bar running east and west.

 

The table below lists these as well as several other galaxies in the area are within range of amateur telescopes.  Be sure to pay homage to each.

 

Members of AGCS 373

(Highlighted entries are discussed above)

Object

RA

Dec

Magnitude

Size

NGC 1310

03 21.1

-37 06.1

13

1.9'x1.5'

NGC 1316

03 22.6

-37 12.8

9.4

11.1'x7.2'

NGC 1317

03 22.7

-37 06.2

11.9

2.5'x2.2'

NGC 1326

03 23.9

-36 27.9

11.5

3.9'x2.8'

NGC 1336

03 26.5

-35 42.8

13.4

2.1'x1.4'

NGC 1341

03 28.0

-37 09.0

13.3

1.5'x1.2'

NGC 1351

03 30.6

-34 51.2

12.4

2.8'x1.7'

NGC 1350

03 31.1

-33 37.7

11.2

5.8'x2.7'

NGC 1365

03 33.6

-36 08.3

10.3

11.3'x6.6'

NGC 1373

03 35.0

-35 10.3

13.3

1.1'x1.0'

NGC 1374

03 35.3

-35 13.6

11.0

2.5'x2.4'

NGC 1375

03 35.3

-35 16.0

12.2

2.2'x0.9'

IC 335

03 35.5

-34 26.8

13.4

2.5'x0.6'

NGC 1379

03 36.1

-35 26.5

11.9

2.3'x2.3'

NGC 1380

03 36.4

-34 58.6

9.9

4.8'x2.7'

NGC 1381

03 36.5

-35 17.7

11.5

2.3'x0.7'

NGC 1380A

03 36.8

-34 44.4

13.4

2.6'x0.8'

NGC 1386

03 36.8

-36 00.0

11.2

3.4'x1.3'

NGC 1387

03 37.0

-35 30.4

10.8

2.8'x2.6'

NGC 1389

03 37.2

-35 44.8

12.6

2.2'x1.3'

NGC 1399

03 38.5

-35 27.0

9.9

6.9'x6.4'

NGC 1404

03 38.9

-35 35.6

10.9

3.4'x3.0'

NGC 1427

03 42.3

-35 23.6

11.8

3.6'x2.4'

NGC 1436

03 43.6

-35 51.2

11.7

2.9'x1.9'

 

 

 

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 challenge.  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 2021 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.

 


  • okiestarman56, John O'Hara, Sasa and 3 others like this


7 Comments

Photo
John O'Hara
Dec 03 2021 07:08 PM

I'm planning to try for it tonight with my 100 f/9 refractor.  I'm hoping I can reach focus w/o the diagonal as it presents a mirror reversed view and I hate the mental gymnastics needed to compare the field to a chart.  I had been using Cartes du Ciel to create transformed charts that matched the view with a diagonal.  However, my old computer crashed and when I uploaded Cartes du Ciel to the new computer, I've had some trouble uploading star catalogues so I can reach a magnitude limit that even a 4" scope will show.   I'll let you know how I come out!

 

John

    • PhilH likes this
Photo
John O'Hara
Dec 04 2021 10:18 PM

I gave it a shot last night with my 100mm f/9 refractor.  The site was within the KOFA National Wildlife refuge south of Quartzsite, Arizona.  This is a dark light gray site on the World Atlas of Night Sky Darkness, and the transparency ranged from about 7/10 to perhaps, at times, 8/10.  The seeing was probably a 4 to 5 on Pickering's scale overhead, certainly no better low on the horizon.  Still, the Southern Arizona local offered 8 degrees more elevation than my native Northern Pennsylvania location.  Armed with a printout of Phil's article, I set up my small scope.  Fortunately, I was just, barely, able to reach focus w/o my star diagonal in place, so I could effectively compare Phil's map with the telescopic view (I'm not great with mental gymnastics).  The approximate time of the observation was somewhere between 9:30 to 10:30 MST.

 

I spent approximately 1 hour on the cluster and could have spent much more time.  The entire session I used a 20 mm Nagler eyepiece giving 45x for a 1.7-degree FOV.  This power may not have been ideal for every galaxy in the cluster, but it did give me an exit pupil hovering just above 2 mm, which is so useful on many DSOs.  With this combination, I was able to spy out:

 

  • NGC 1365 which was bright, large and elongated;
  • NGC 1386, visible with averted vision;
  • NGC 1387, visible with direct vision and grew in extent with averted vision;
  • NGC 1399, round, visible with direct vision;
  • NGC 1404, visible with direct vision, grew with averted vision;
  • NGC 1373, 1374 and 1375 were suspected, but at that, as one amorphous glow and not seen individually.

I don't feel my 1-hour session did this cluster justice.  For example, I did not view the SW portion of the cluster that contains one of the cluster's brighter members, NGC 1316.  Also, a more thorough attempt would have included trying higher magnification to see if I could tease out some of the objects with smaller angular diameters.  But I had fun, and very much appreciate Phil's articles and books.  I hope some others give this cluster a try.  

 

John

    • PhilH, Knasal, HeathM98 and 2 others like this

Nice report, John!  Thanks for sharing.  I am glad that you had a chance to grab some of the Fornax Cluster through your scope.  Sounds like a great observing site.

 

I first became interested in the cluster after I noticed it on the original Sky Atlas 2000.  It was shown on the Skalnate Pleso also, but most of the galaxies were unidentified there. But even with the SA2000, trying to figure out which I was seeing through my 8" RV-8 was tough. Then along came the Uranometria atlas and everything started to make sense.  smile.gif

    • John O'Hara likes this

Thank you for the history lesson.  As always, a pleasure to read your words and learn from you.  Much appreciated.  

    • PhilH and John O'Hara like this
Photo
John O'Hara
Dec 15 2021 04:40 PM

Nice report, John!  Thanks for sharing.  I am glad that you had a chance to grab some of the Fornax Cluster through your scope.  Sounds like a great observing site.

 

I first became interested in the cluster after I noticed it on the original Sky Atlas 2000.  It was shown on the Skalnate Pleso also, but most of the galaxies were unidentified there. But even with the SA2000, trying to figure out which I was seeing through my 8" RV-8 was tough. Then along came the Uranometria atlas and everything started to make sense.  smile.gif

Phil,

 

Have you checked out the Interstellarium Deep Sky Atlas?  I've long been a user of Uranometria, but the IDSA is one nice handy volume.  It's not perfect and perhaps doesn't go quite as deep, but it's so handy at the scope.  Think of it as a Jumbo Pocket Sky Atlas amped up.

 

John

Phil,

 

Have you checked out the Interstellarium Deep Sky Atlas?  I've long been a user of Uranometria, but the IDSA is one nice handy volume.  It's not perfect and perhaps doesn't go quite as deep, but it's so handy at the scope.  Think of it as a Jumbo Pocket Sky Atlas amped up.

 

John

Must admit that I do not own the IDSA.  I'm old school, I guess, and prefer Megastar for *really* fine detail.  Actually, I use a three-pronged approach.  Since I always star-hop, I have both SA2000 and Uranometria open to my selected target(s), but then use printed charts from Megastar when necessary to find the tough ones.

 

Phil

    • John O'Hara likes this
Photo
John O'Hara
Dec 19 2021 07:28 PM

I got Cartes du Ciel on my computer and was finaly able to download deep star catalogues.  I do much the same as you do with Megastar, printing out charts for use at the scope that have a limiting magnitude near that of the main scope.  I'm an old school star hopper myself, with no plans to change anytime soon.  I'm looking forward to takeing on more of your small to medium scope challenges while in Arizona this winter.  Thanks for all you do to keep our hobby interesting and challenging!

 

John



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