Alpha Persei Cluster (Melotte 20 – Collinder 39)


The Perseus constellation is always welcome in my pictures. From the first time I caught it in an image, I was almost certain it would contain some amazing deep sky objects (things other than single stars). However, other than the double cluster and the Spiral Cluster hanging out on the fringe of the constellation, there are no obvious objects. Sure, there are telescope items for sure, but none as obvious as things in, say, Orion or Canis Major. 

So, why did I assume this hunk of sky contained deep sky treasure? There is a distinct stream of concentrated stars. Even in photos in which I used no zoom, it still draws the eye. So I decided to magnify it by 35, but that is slightly too much. 30x and below seemed to work best, unless you wanted to create a mosaic with a handful of zoomed shots.

Last year while Perseus was up I couldn’t find any Messier objects and moved on. Now with extra experience under my belt, I know better. This distinct stream had to be something. At minimum I believed I would find that it is an exposed arm of the galaxy that we are seeing through a window of dust, similar to the Sagittarius Star Cloud.

After shooting this I came home and began researching. I learned that this stream in it’s entirety is actually a cluster. More specifically, it is what’s known as a moving group. Open star clusters are not bound to one another for eternity. Most of them break apart. However, some clusters stay mildly intact and all orbit the Sun, together. Even though it is still seems relatively compact from our point of view (500-600 light years), if it were a mere 100 light years away it would appear as stars spread across the sky, similar to another cluster/moving group that most people do not know of.

The cluster I am referring to is the Ursa Major (Big Dipper) Moving Group. Most of the stars were once in a cluster together and have spread out a tad. If we were a few hundred light years away, it might still appear as a wide cluster. Yet since most of it’s stars are around 100 light years away, they appear as scattered stars.

Enough rambling. Perseus is a great constellation. Grab binoculars and go look! The Alpha Persei Cluster/Moving Group is one of the easiest and most rewarding objects to gaze at. Absolutely stunning.

(A closer photo)



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