NGC 7160, Open Star Cluster
The star cluster NGC 7160 is located at a distance of only about 2,600 light years in the constellation Cepheus. It was found in 1787
by F.W. Herschel.
Due to its small distance it appears to us under a rather large apparent angular extent of 13' (minutes of arc). The core diameter of the
cluster is given as 5 light-years, but stars are still gravitationally bound to the cluster up to a distance of 18 light-years.
A total of 16 stars are located in the core region of NGC 7160, while another 70 stars also belong to the cluster. The brightest star is
a so-called variable with the designation "EM Cep", which belongs to the class of Be- stars just like "Archernar". These stars are
characterized by high rotation velocities and therefore can be strongly flattened. This has for example the consequence that the polar
regions are hotter than the regions near the equator.
The age of NGC 7160 is given with 10 to 19 million years - so the cluster is very young by cosmic standards.
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In my 20" f/3 Dobsonian, NGC 7160 looks great. Since the cluster is quite large, the best view is at a magnification of V=210x. Four
bright stars are very conspicuous - the brightest of them (EM Cep) shines with 7.1mag glistening bright and whitish in the eyepiece.
These four stars are nearly in the center of the cluster and are surrounded by 30 other member stars, which are much fainter with 10
to 12mag. The cluster as a whole is roundish, but still shows an irregular outer shape. Especially in the southwestern part there are
less stars.
All in all a great cluster for a starry summer night.
