The Double Cluster is more formally known as h and Chi Persei, or NGC 884 and NGC 869. It resides in the northern part of the constellation Perseus, quite close to the constellation Cassiopeia the Queen.
The Double Cluster has to rate as one of the most magnificient deep-sky objects NOT to have been listed in the famous Messier catalogue. Of course, Charles Messier (1730-1817) was only interested in cataloguing deep-sky objects that could be mistaken for comets. Apparently, he thought nobody would see this pair of glittery clusters as a comet in the sky.
Although considered a deep-sky jewel, the Double Cluster is visible to the unaided eye in a dark country sky. If you zoom in on these rather feeble-looking stellar blobs with binoculars or a wide view telescope, they all of a sudden turn into two glorious star clusters.
How to find it
At mid and far northern latitudes, the Double Cluster is circumpolar – above the horizon every night of the year at any hour of the night. Yet, the Double Cluster is harder to see when it’s close to the horizon, so it’s best to look when the Double Cluster is somewhat high in the sky.
For general reference, the Double Cluster is high in the sky when the Big Dipper is low, and vice versa. Because the Big Dipper is lowest in the northern sky on late autumn and early winter evenings, the Double Cluster is highest in the northern sky at these times. The Double Cluster is pretty much always visible at evening except in late spring and summer.
Even in middle August, you can see the Double Cluster from late night till dawn. The annual Perseid meteor shower peaks around August 12 or 13, and if you trace the paths of these Persied meteors backward, they appear to originate near the Double Cluster.
To locate the Double Cluster, find the W or M-shape constellation Cassiopeia the Queen. (It looks like a W when low in the sky and an M when high in the sky.) Draw an imaginary line from the star Navi (Gamma Cassiopeiae) through the star Ruchbah (Delta Cassiopeiae), and go about 3 times the Navi/Ruchbah distance to locate the Double Cluster.
The Double Cluster is thought to be over 7,000 light-years distant, and to be separated from one another by a few hundred light-years. It is amazing that we can see these stars at all across this great span of space. Each cluster contains a few hundred stars, harboring young, hot supergiant suns that are many thousands of times more luminous than our sun.
Astronomers tell us that the Double Cluster lies within the Perseus arm of the Milky Way galaxy. However, our solar system resides in the inner part of the Orion arm. Therefore, when we look at the Double Cluster, we are looking through our local spiral arm and all the way to the next spiral arm outward from the galactic center.
The two star clusters making up the Double Cluster are called NGC 869 (h Persei) and NGC 884 (chi Persei).
h Persei’s position is Right Ascension: 2h 19m; Declination: 57o 9′ north
chi persei’s position is Right Ascension: 2h 22.4m; Declination: 57o 7′ north