Alpha Persei Cluster

The α - Persei group also Melotte 20 and Collinder 39, is an open star cluster in the constellation Perseus, which can be observed with the naked eye. The cluster consists of a relatively large number with the naked eye visible stars around the main star of the constellation Perseus around.

The brightest star of the cluster is α Per ( Mirphak ), a star of spectral type F5 with a brightness of 1.8 mag. More bright members are δ, ε, ψ, 29, 30, 34 and 48 Persei. The total brightness of the cluster is about 1.2 mag.

Due to its size and brightness of this star cluster has been known since ancient times, like many other star clusters that have a very small distance from the Earth, and therefore have a large apparent diameter ( for example, the Ursa Major group or the Hyades ); he was not included in the modern standard catalogs Messier, NGC and IC. Only P. J. Melotte took the pile of 1915 in his catalog of open star clusters. Under the name of the cluster Cr 39 is also to be found in the catalog of Per Collinder.

It is also interesting that this cluster is a so-called moving clusters, ie the stars all have a similar proper motion. Even physically the stars are very similar, because with a few exceptions ( including α and σ per) they are of spectral type O or B. The cluster is part of a so-called OB association. The age of the cluster is estimated at about 50-70 million years.