Alpha Persei Cluster

open cluster in the constellation Perseus

The Alpha Persei Cluster (also known as Melotte 20 or Collinder 39) is an open cluster in the constellation of Perseus.

Alpha Persei Cluster

To the naked eye, the cluster has 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 show the cluster as about ~172 parsecs away from us.[1][2]

Since the distance by the independent analyses agree, the cluster is an important rung on the cosmic distance ladder. The age of this cluster is about 50–70 million years.[3][4]


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