NGC869/884: The Double Cluster
This is a pair of clusters, separately catalogued as NGC 869 and NGC 884, but generally known as a pair called “The Double Cluster”.
Open clusters are easy to find and observe in small telescopes, pretty, and scientifically important. This is a group of stars all born from a common cloud of gas and dust. Since they came from the same gas cloud they are, astronomically speaking, all about the same age and all about the same distance from us, and they all started with about the same chemical composition. Knowing that they are the same age and at the same distance, the fact that they have different appearances allows us to learn a great deal about stellar evolution – the different appearances can only be a result of the different masses of the different stars.
Finding the Double Cluster
For convenience, let’s name two of the stars.
The star in the centre of the “W” is ”Gamma Casiopeiae.” The next star out toward the stretched, lopsided side of the “W” is ”Ruchbah”.
In a magnifying finder you should be able to see two brighter patches of light against the background stars. Centre those.
Now switch to your telescope, with your widest-field eyepiece.
In your main telescope, you will see two distinct clusters, each with their own bright core of stars.
This image simulates the view in dark skies at about 35x magnification.
The Double Cluster is very large. In long-focal-length telescopes (such as mid-sized SCTs) you may not be able to fit both clusters in the view unless you have a very wide-field eyepiece. In such a case, it may look better in your magnifying finder scope, or in binoculars.
All the above images were generated with Starry Night Pro.