NGC 188, Open Star Cluster
The open star cluster NGC 188 can be found at a declination of +85° and therefore belongs to the most northern star clusters in the sky. It is
located at a distance of 5,400 light years in the constellation Cepheus and was discovered in 1825 by the British astronomer John Herschel.
Since NGC 188 is located above the galactic plane and therefore the light is not affected by dust masses, it is a grateful object for scientific
studies. The cluster contains about 5,000 stars with a total mass of 620 solar masses. The brightest stars reach a brightness of a little more
than 12mag, which corresponds to an absolute luminosity of 45 suns at this distance. The core diameter is given with 11.8 lightyears, but
the stars are gravitationally bound to NGC 188 up to a distance of 40 lightyears.
Due to the high mass of the cluster and its position above the galactic disk it has not been torn apart by tidal forces in all this time. With an
age of 6.8 billion years the cluster is one of the oldest known star clusters.
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In a 20 inch telescope NGC 188 appears faint at a magnification of 120x, but still quite conspicuous. There are about 20-25 single stars visible.
The most beautiful view is at 210x. Now about 70-80 single stars are visible, among them 10 brighter ones. The cluster as a whole appears
roundish and tapers gently outwards. The star density increases slightly towards the center, but the stars are not evenly distributed, there are
star clumps and star-poor areas inside. The stars are quite variable in brightness, but almost all fainter than 13mag.
