Berkeley 56, Open Star Cluster
The star cluster "Berkeley 56" belongs with a distance of an immense 40,000 light-years to the most distant representatives of its kind.
A recent study from 2018 gives the distance as 39,500 light-years.
The apparent diameter can be determined by the DSS to be 3.4 arcminutes, resulting in a true diameter of 39.6 light-years. This is a very
large value for an open star cluster. Furthermore "Berkeley 56" seems to be very old with an age of 4.1 billion years. Therefore it is
one of the oldest known star clusters.
Due to the huge distance only a handful of stars brighter than 16.5mag can be found in the cluster. With the known distance their
absolute brightness can be calculated to M= +1.0mag, which is about 30 times the luminosity of the Sun. However, the very largest
fraction of stars has an apparent magnitude of less than 18mag and is therefore visually unobservable even in very large telescopes.
By the way, the largest fraction of stars can be found at a brightness of V=20mag.
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Even in a 20 inch telescope "Berkeley 56" appears only as an extremely faint brightening, difficult to hold even at a magnification of
270x with indirect vision. The patch of nebula appears uniform and round. Despite the high magnification there are absolutely no
single stars visible that could actually be attributed to the cluster. Only some foreground stars are visible.
The Milky Way is quite dense in this area, so at least the surrounding area is a bit interesting.
