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NGC 869 and NGC 884 are two bright open clusters in the constellation of Perseus that are separated by only half a degree of apparent sky. Together they are commonly known as the "Double Cluster" and form a famous showpiece object that's easily visible to the naked eye and a wonderful sight in binoculars and telescopes. It appeals to all types and sizes of optical scopes. Both clusters have been known since antiquity and probably pre-historically. Greek astronomer Hipparchus first catalogued them around 130 B.C with early celestial cartographers naming them as "h Persei" (NGC 869) and "χ Persei" (NGC 884).

The Double Cluster is located in the far northwestern part of Perseus close to the border with Cassiopeia. With a declination of 57N it's circumpolar from many northern locations and therefore never sets. To locate the object draw an imaginary line from Mirfak (α Per - mag +1.8) in a northwesterly direction towards the centre of the famous "W" of Cassiopeia. The Double Cluster lies just over halfway along this line. It's listed as number 14 in the Caldwell catalogue.

C14 - NGC 884 - NGC 869 - The Double Cluster (Michael Fulbright - MSFAstro.net - http://msfastro.net)

Finder Chart for C14 - NGC 869 and NGC 884

Finder Chart for C14 - NGC 869 and NGC 884 - pdf format

To the naked eye the Double Cluster appears like a large unresolved detached part of the Milky Way. The view through binoculars is addictive, a breath-taking sight with both clusters each covering more than half a degree of sky and almost touching. It looks like a hazy mist sprinkled with two regions of blue and white stars surrounded by many unrelated Milky Way stars. NGC 869 at magnitude +4.3 is marginally the brighter richer cluster while NGC 884 glows at magnitude +4.4. The brightest individual stars shine at 7th magnitude. The extra aperture and magnification provided by small scopes reveals two large bright compact clusters with dozens of stars visible concentrated towards the cluster centres. Many other fainter stars are scattered throughout. A 200mm (8-inch) telescope further enhances the impact showing several hundred bright blue and white stars that completely fill the field of view. There are strands of bright blue and white A and B type supergiants streaming outwards from the cores in curving patterns with a few fainter M type supergiant red stars in and around cluster NGC 884.

Recent data measurements put the distances of NGC 884 and NGC 869 at 7,600 and 6,800 light-years from Earth respectively. Both clusters are extremely young and physically close to one another in space. It's estimated that NGC 869 is 5.6 million years old and NGC 884 only 3.2 million years old. For comparison M45 the Pleiades open cluster is 115 million years old.

It's no accident due to young age that NGC 869 and NGC 884 contain together at least 400 hot blue-white supermassive and super luminous giant stars.

NGC 869 Data Table

NGC869
Caldwell14
Nameh Per
Object TypeOpen Cluster
ConstellationPerseus
Distance (kly)6.8
Apparent Mag.4.3
RA (J2000)02h 19m 03s
DEC (J2000)57d 08m 06s
Apparent Size (arc mins)35 x 35
Radius (light-years)35
Age (years)5.6M
Number of Stars250
Other NamesCollinder 24, Melotte 13

NGC 884 Data Table

NGC884
Caldwell14
Nameχ Per
Object TypeOpen Cluster
ConstellationPerseus
Distance (kly)7.6
Apparent Mag.4.4
RA (J2000)02h 22m 32s
DEC (J2000)57d 08m 39s
Apparent Size (arc mins)35 x 35
Radius (light-years)38
Age (years)3.2M
Number of Stars200
Other NamesCollinder 25, Melotte 14