Alpha Persei Cluster

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Alpha Persei Cluster
Alpha Persei Cluster.png
Observation data (2000.0 epoch)
Constellation Perseus
Right ascension 03h 26.9m
Declination +49° 07′
Distance 557-650 ly[1][2][3] (171-200 pc)
Apparent magnitude (V) 1.2
Apparent dimensions (V) 185'
Physical characteristics
Other designations Cr 39, Mel 20
See also: Open cluster, List of open clusters

The Alpha Persei Cluster, also known as Melotte 20 or Collinder 39, is an open cluster in the constellation of Perseus. To the naked eye, the cluster consists of several blue spectral type B type stars. The most luminous member is the ~2nd magnitude white-yellow supergiant Mirfak, also known as Alpha Persei. Bright members also include Delta, Sigma, Psi, 29, 30, 34 and 48 Persei. The Hipparcos satellite and infrared color-magnitude diagram fitting have been used to establish a distance to the cluster of ~172 pc.[2][3] The distance established via the independent analyses agree, thereby making the cluster an important rung on the cosmic distance ladder. The age of this cluster is about 50-70 million years.[1][4]


Designations Spectral type
Luminosity class
α Per (33 Per) F5Ib
δ Per (39 Per) B5III
ε Per (45 Per) B1V
ψ Per B5Ve
29 Per B3V
30 Per B8V
34 Per B3V
48 Per B3Ve


  1. ^ a b Prosser, Charles F.; Randich, Sofia; Stauffer, Joh R.; Schmitt, J. H. M. M.; Simon, Theodore (October 1996). "ROSAT Pointed Observations of the Alpha Persei Cluster". Astronomical Journal. 112: 1570. Bibcode:1996AJ....112.1570P. doi:10.1086/118124. 
  2. ^ a b van Leeuwen, F. "Parallaxes and proper motions for 20 open clusters as based on the new Hipparcos catalogue", A&A, 2009
  3. ^ a b Majaess, D.; Turner, D.; Lane, D.; Krajci, T. "Deep Infrared ZAMS Fits to Benchmark Open Clusters Hosting delta Scuti Stars", JAAVSO, 2011
  4. ^ Paunzen, E., Mermilliod, J.-C. "WEBDA: Alpha Persei"

External links[edit]

Coordinates: Sky map 03h 22m 00s, +49° 00′ 00″