Perseus is still in good position in early February, high in the North-West around 9:00 PM EST for Northern mid-latitude observers. Perseus holds a few open clusters for owners of small telescopes such as M34, NGC 1245 and of course the Double Cluster (NGC 884 and NGC 869). But I want to turn your attention to a cluster that is mostly ignored by backyard astronomers, partly because it doesn’t appear on many sky atlases and it is rarely mentioned in articles. That object is known as The Alpha Persei Cluster, also cataloged as Collinder 39 and Melotte 20. The Alpha Persei cluster takes its name from the constellation’s brightest star, Alpha Persei (Mirfak) which is a member of the cluster. The cluster is about 50 million years old -just one percent of the age of the Sun and lies some 600 light-years away in the rich star fields along our galactic plane.
Many astronomers refer to this cluster as an association because it is loosely bound by gravity. This loose type of open cluster is also
called an OB-Association since the clustered stars are mainly of the young, massive, and hot spectral types O and B. These associations are quite unstable and have short lifetimes before they evaporate into space. The cluster is not rapidly dispersing but its members are moving in the same direction.
The Alpha Persei Cluster is easy to locate simply by looking at Mirfak (Alpha Perseus) in the constellation Perseus. To the naked eye, the cluster consists of several stars of spectral type B, along with the most massive member — the F5 supergiant Alpha Persei. The brightest members of this cluster include Alpha, Delta, Epsilon, Psi, 29, 30, 34 and 48 Persei. Binoculars or a rich-field telescope give the best view of the Alpha Persei cluster. Keep the magnification under 20x and even at such low power, you’ll see about 50 bright stars from a dark sky site, and somewhat less under light polluted skies. All told, more than 100 young stars brighter than magnitude 12 spread across the association’s 3° width.
I have provided a finder chart showing the Alpha Persei Cluster just in case your atlas doesn’t show the cluster. You can download it here.
Until next time, clear skies!