The Double Cluster, two open star clusters in Perseus

The Double Cluster, two open star clusters in Perseus

Image Credit & Copyright: Roth Ritter, Dark Atmospheres Astrophotography (

The Double Cluster (also known as Caldwell 14) consists of the open star clusters NGC 884 and NGC 869 which are close together within the Perseus arm of the Milky Way galaxy, in the constellation Perseus, quite close to the constellation Cassiopeia. NGC 884 (left) and NGC 869 (right) are at distances of 7600 and 6800 light-years away, respectively. The Double Cluster represents the jeweled handle of Perseus’s sword.

The clusters are blueshifted, with NGC 869 approaching Earth at a speed of 22 kilometers per second and NGC 884 approaching at a similar speed of 21 kilometers per second.

Separated by just a few hundred light-years, each cluster contains hundreds of young, hot stars, much younger and hotter than the Sun. Among them are more than 300 blue-white super-giant stars, that are many thousands of times more luminous than our Sun, and a few orange stars. The clusters are both part of the so-called Perseus OB1 association, an assembly of extremely massive stars.

The clusters’ ages, based on their individual stars, are pretty young. NGC 869 is 5.6 million years old and NGC 884 is 3.2 million years old, making them among the youngest star clusters known in the galaxy. In comparison, the Pleiades are over 100 million years old.

Open clusters are believed to originate in the same general area of space from the same local gas clouds. Due to their age similarities, it is likely that both NGC 884 and NGC 869 were a product of the same star-forming region.

The Double Cluster is a great target for binoculars and small telescopes, but also visible to the unaided eye from dark locations as a hazy patch. It nearly marks the radiant point of the Perseid meteor shower, which peaks annually around August 12 or 13.

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