Teutsch 156, Open Star Cluster
The star cluster "Teutsch 156" is located in the constellation Cygnus north of NGC 7000 and lies at the edge of an extensive dark nebula.
The distance is given with about 26,000 light-years, with an error of +-3100 light-years. At least it can be stated that the star cluster is
quite far away from Earth. Despite the large distance "Teutsch 156" has an apparent diameter of 2.6' (arcminutes), which corresponds
to a true size of 20 light-years. This is quite a lot for a star cluster.
The large distance is also the reason why the brightest stars have a brightness of only 15mag. Altogether 130 stars down to a brightness
of 18mag are attributed to the cluster.
The age is given with 720 million years, so the cluster is one of the older of its kind.
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I could observe the cluster in a warm September night in my 20" f/3.2 Dobson. "Teutsch 156" was best visible at 270x and showed a roundish,
slightly irregular cloud with a grainy background. I could see 15 single stars with indirect vision, but from the nebulous glow some fainter stars
flashed out every now and then. Even the edge of the dark cloud was well visible, because very faint stars are almost completely missing.
So if you want to see a very distant star cluster at the edge of a dark cloud, I can only recommend "Teutsch 156". :)
