Alpha Persei Cluster

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 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.van Leeuwen, F. "Parallaxes and proper motions for 20 open clusters as based on the new Hipparcos catalogue", A&A, 2009Majaess 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 

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 5070 million years.Paunzen, E., Mermilliod, J.-C. "WEBDA: Alpha Persei"

 References 

Category:Open star clusters