Galaxy clusters are among the largest and most impressive structures in the universe and can stretch up to 20 million light years. In such a cluster, up to 1,000
galaxies are gravitationally bound to each other and move through the cluster at up to 1,000 kilometers per second. The total mass can be up to 1 quadrillion
solar masses. The main part, however, is not the galaxies themselves, but mainly the dark matter, which makes up to 80% of the mass. A galaxy cluster is also
penetrated by up to 100 million Kelvin hot gas filaments, which represent 15% of the total mass. So, the visible galaxies account for only 5% of the total mass.
Since the dark matter and the hot gas cannot be observed in an amateur telescope, the focus of the observation of these huge and enormous structures is on the
individual galaxies. Of course, galaxy clusters that are quite close to us are particularly interesting. The Virgo cluster at a distance of about 60 million light years
is probably the best known. But even clusters in a distance of some hundred million light-years are very impressive in telescopes of more than 40cm aperture.
In some of these galaxy clusters a huge elliptical galaxy lurks in the center, surrounded by many other small galaxies. In the eyepiece this is a wonderful sight.
Of course, the farther away the galaxy clusters are, the more difficult it becomes to spot individual galaxies. With 20" aperture, however, the Corona Borealis
Cluster, for example, is a very worthwhile target - despite the huge distance of 1 billion light years.
1) Galaxy Clusters from the Abell Catalog
#1- 999:
#1000-1999:
#2000-2999:
2) Andere Galaxienhaufen
