The Double Cluster (also known as Caldwell 14) consists of the
open cluster
An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...
s
NGC 869 and
NGC 884 (often designated h Persei and χ (chi) Persei, respectively), which are close together in the constellation
Perseus
In Greek mythology, Perseus (Help:IPA/English, /ˈpɜːrsiəs, -sjuːs/; Greek language, Greek: Περσεύς, Romanization of Greek, translit. Perseús) is the legendary founder of Mycenae and of the Perseid dynasty. He was, alongside Cadmus ...
. Both visible with the naked eye, NGC 869 and NGC 884 lie at a distance of about 7,500 light years in the
Perseus Arm of the
Milky Way
The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked ey ...
galaxy
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar Sys ...
.
Membership
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.
They form the core of the
Perseus OB1 association of young hot stars.
Based on their individual stars, the clusters are relatively young, both 14 million years old.
In comparison, the
Pleiades
The Pleiades (), also known as The Seven Sisters, Messier 45 and other names by different cultures, is an asterism and an open star cluster containing middle-aged, hot B-type stars in the north-west of the constellation Taurus. At a distance ...
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 and NGC 884 approaching at a similar speed of . Their hottest main sequence stars are of