Basel 1, Open Star Cluster
Basel 1 is an open star cluster in the constellation "Scutum". Because it is only about 1° east of Messier 11 in the middle of a prominent asterism,
it is quite easy to find.
The cluster is 5,200 lightyears away from us, but there are also deviating values of 7,100 lightyears. With an apparent size of 4-5 arcminutes the true
diameter is just under 7 lightyears. Altogether 31 stars seem to belong to "Basel 1", the brightest of them with a visual magnitude of 11.6mag which
corresponds to a luminosity of 50 suns. The earliest observed spectral type is B5. Some red giant stars have been found in the area of the cluster, but
after a comparison with the surrounding area they are probably only randomly distributed field stars.
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In my 50cm f/3.2 Dobsonian, at a magnification of 120x, a loose cluster of stars can be seen, but it still stands out well from the surrounding star field.
The shape is roundish with the impression of a slightly increased stellar density towards the center. In total about 45 stars can be seen in the area, but
some of them do not seem to belong to the cluster. The most beautiful view is at 210x, because now fainter stars appear. A small cluster of stars in the
southeastern part of the cluster is conspicuous.
