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:
abell1656_lrgb.jpg
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:
A1656_60_60F.jpg
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!"
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