Object Of The Week April 15, 2018: Abell 1656

Abell 1656, ACO 1656, Coma Cluster

Cluster of Galaxies

Constellation: Coma Berenices
RA: 12 59 48.7
DEC: +27 58 50

Mag 10th brightest member: 13.5

Size: 319'

In 1958 George Abell published a list of 2712 rich clusters of galaxies with nominal redshift ≤ 0.2. In 1989 co-authors Harold Corwin and Ronald Olowin added another 1361 clusters from those parts of the south celestial sky that were left out from the earlier survey. So today there are 4073 Abell or ACO clusters, the name depending on what source you use.

The Coma Cluster is thought to contain over 1000 galaxies. Together with another great and beautiful cluster Abell 1367 it is one of the two main clusters forming the Coma Supercluster, which, at about 300 million lightyears, is the closest supercluster after our own local Virgo Supercluster. In 1933 Fritz Zwicky showed that the individual cluster members of the Coma Cluster were moving too fast to be gravitationally bound by the visible matter. He wrote that the cluster members must be bound together by some dunkle Materie but the idea of dark matter wouldn't be accepted for another 50 years.

Most cluster members are elliptical and S0 galaxies. The few spiral galaxies can mostly be found in the outskirts of the cluster.

Many years ago I observed the Coma Cluster with my homemade 6" Newtonian telescope an, unsurprisingly, I only managed to see three galaxies: NGC 4874 en 4889 (the two brightest, central galaxies) and NGC 4911.

Last night I finally revisited the cluster after having seen this fantastic image of the cluster created by Belgian amateur Bart Delsaert:

Attachment 2981

For more info about the photo, see Bart's website.

I was using the map created by Albert Highe. His website contains very interesting info about 7 Abell clusters, among which Abell 1656. He even provides a 60'x60' finder map with all galaxies labeled on it. This is the map:

Attachment 2982

I simply printed the map on two sheets of paper (one sheet would do but I couldn't read the small print) and tried to at least see all NGC and IC galaxies on the map. At first I centered the cluster in the 54' FOV at 83x and already could see several galaxies. Next I switched to 320x and 19' and started to systematically locate and identify the galaxies I saw. I started at NGC 4889 and worked my way clockwise from the south east around the center. Since I only started at midnight and had to get up early today, I mainly focused on identifying what I saw and didn't pay much attention to all details, nor did I try to squeeze every photon out of the SQM 21.1 sky. I therefore skipped many of the fainter MCG and PGC galaxies, though I did see several.

About an hour later I had identified 69 galaxies. These included almost all NGC and IC galaxies. I skipped NGCs 4842A and B (in the lower right corner of the map) and NGCs 4926, 4926B and 4927 (to the left edge of the map) because they were a bit too far out. And I also managed to see 5 MCGs, 2 CGCGs and 2 PGCs.

As can be seen on Bart's website there is a mag 20 quasar just to the north east of IC 3959. It is too faint to be seen with my 20" telescope but maybe someone with a (much) larger telescope can give it a try?

Then there is a galactic planetary nebula marked as PLN49+88 close to the lower edge of the map. This planetary nebula actually is called H4-1 and was discovered by Guillermo Haro in 1951. I located the planetary nebula at 320x and it was visible as a faint star. When I used my OIII filter all other stars disappeared but the planetary nebula remained visible.

I am sure I should be able to squeeze more out of the Coma Cluster but even this hasty observation hour was very, very rewarding. I am curious to know what you have seen!


As always,

"Give it a go and let us know!
Good luck and great viewing!"

Good job Wouter! This will be a nice observing program for people. My observations of PN H 4-1 is much like your observation. I first tracked down this small stellar PN in the late 1990's with my old 25". I will try for the qusar QSO HB89 1259+280 next time I am observing with the 48". Thanks for the "heads up" about this object.

Hi All,

Here is my observation of the core of Abell 1656, with a 25" Obsession, under a rather good sky ( SQML 21.76, NELM ~7.0v, FWMH 1.75)

Attachment 2983

report at http://www.deepsky-drawings.com/agc-...ter/dsdlang/en
Overall, I could see 41 galaxies up to m17.5v, in a rectangle of about 20' x 10'.
In the same area, I have seen a small dozen of galaxies with a LX200 10", some years before.

Clear skies
Bertrand
http://www.deepsky-drawings.com/dsdlang/en/

I had to take a deep breath before this one. I found out three year ago how I wanted to draw it and then managed to realise the project in 2 very busy nights. It is a panorama drawing: I drew the 28 brightest stars into my sketchbook from a map (Guide) and then I drew all the rest by the telescope. This predrawing was unfortunately nesessary because the area I chose was much larger than a field of view. And I just can't get the proportions right that way.

16" f/4.4, 170x (10 mm Delos) - 225x (8 mm Planetary), 2015.03.19/20-20/21. Ágasvár, Hungary
Attachment 2984

And the inverted version:
Attachment 2985

I didn't use a map/photo while drawing - I wanted to find the galaxies myself. And I was very happy because I managed to find many of them. Though I drew some galaxies as stars. Unfortunately there very practically no details in any of them.

I'm very curious if you have seen any details in the spirals NGC 4921 and 4911 with bigger scopes. The Hubble photos area amazing.

That is a really impressive drawing Peter! It is almost as if I am back at the eye piece.

I didn't notice any details in the spiral galaxies but I didn't really pay attention to that. I just wanted to get all NGC and IC galaxies in as short a time as possible :P

Wow, what a highlight Wouter. One of the finest cluster in the sky indeed. I looked at it with several apertures but concentrated myself with two apertures, my 8-inch and 27-inch.

With 8-inch it makes not yet fun to observe the cluster. Except both main galaxies it was a fight for every other single galaxy. In an "open" field of approx 30' I could catch 21 galaxies.
sketch 8", 160x-229x, seeing III, NELM 6m0+
Attachment 2986

The 27-inch of course had an easy game. I had to limit the field to 18' which represents the field through amid power eyepiece. Higher magnifications (up to 586x) shows higher limiting magnitude of the single galaxies and interesting details like the edge-on companion of NGC 4884 (=NGC 4889) or the close double system of NGC 4898. When I count right I got 60 galaxies within the field. Hard work to see and sketch all fuzzy balls but worth the time.
sketch 27", 293x-586x, seeing II, NELM 6m5+
Attachment 2987

I tried for the quasar HB 89 1256+280 near I C 3959 the other night under poor seeing conditions and had no luck I tried for a long time with no luck. Last Thursday night with Steve Gottlieb with me we had excellent transparency and seeing so I gave the quasar another try. I was much surprised when at the right location that I got a flash that would come and go with the seeing. The longest that it appeared was for a count of three seconds. I was really pleased to catch the 11.3 billion light year light even if it was just a flash at a V Mag of 20.3 from the Sloan Photometry. I used 610X and 813X for the observation.

Attachment 3054

That's an impressive observation Jimi, even with a 48" telescope!

Yes I was surprised and pleased that I was able to catch it after getting skunked the first time I tried it. Nothing like catching billion year old light!! :shocked:

The mag 20 quasar was really a threshold object for me with only a few pops. But without knowing the precise location, I noted at the eyepiece it formed a right angle with IC 3959 and IC 3963. Jimi confirmed that was the exact position, while checking the DSS image at his desk in the observatory.