The Double Cluster in Perseus
Object Type: Open Cluster
Scope: APO 5" AP Refractor
Exposure 230 minutes
Scope: APO 80mm regractor
Exposure 70 minutes
The Double Cluster (also known as Caldwell 14) is the common name for the naked-eye open clusters NGC 884 ( Persei) and NGC 869 (h Persei), which are close together in the constellation Perseus. NGC 884 and NGC 869 are at distances of 7600 and 6800 light-years away, respectively, so they are close to one another in space as well. The clusters' ages based on their individual stars are similar, in addition to their physical proximity.
NGC 869 has a mass of 4,700 solar masses and NGC 884 weighs in at 3,700 solar masses; both clusters are surrounded with a very extensive halo of stars, with a total mass for the complex of at least 20,000 solar masses.
Based on their individual stars, the clusters are relatively young, both 14 million years old. In comparison, the Pleiades have an estimated age ranging from 75 million years to 150 million years.
There are more than 300 blue-white super-giant stars in each of the clusters. The clusters are also blueshifted, with NGC 869 approaching Earth at a speed of 39 km/s (24 mi/s) and NGC 884 approaching at a similar speed of 38 km/s (24 mi/s).
In mythology Perseus was a famous hero of Greek mythology, a son of the Greek god Zeus. Along with beheading Medusa, Perseus performed other heroic deeds such as saving princess Andromeda who was chained to a rock as a sacrifice to a sea monster, Cetus. The gods commemorated Perseus by placing him among the stars, with the head of Medusa in one hand and the jeweled sword in the other. The Double Cluster represents the jeweled handle of his sword.