The Double Cluster (also known as Caldwell 14) is the common name for the naked-eye open clusters NGC 884 and NGC 869 (sometimes designated χ Persei and h Persei, respectively, but those designations would really apply to both clusters and to a visually nearby star), 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 also close to one another in space. The clusters' ages, based on their individual stars, are relatively young. NGC 869 is 5.6 million years old and NGC 884 is 3.2 million years old, according to the 2000 Sky Catalogue. 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 22 km/s (14 mi/s) and NGC 884 approaching at a similar speed of 21 km/s (13 mi/s). Their hottest main sequence stars are of spectral type B0.
Read more about Double Cluster: Mythology, History, Location
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