The Melotte catalogue is a catalogue of 245 star clusters compiled by British astronomer Philibert Jacques Melotte. It was published in 1915 as A Catalogue of Star Clusters shown on Franklin-Adams Chart Plates. Catalogue objects are denoted by Melotte, e.g. "Melotte 20". Dated prefixes include as Mel + catalogue number, e.g. "Mel 20".

The Alpha Persei Cluster, also known as Melotte 20 or Collinder 39, is an open cluster of stars in the northern constellation of Perseus. To the naked eye, the cluster consists of several blue-hued spectral type B 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 ~560 light-years (172 pc). The distance established via the independent analyses agree, thereby making the cluster an important rung on the cosmic distance ladder. As seen from the Earth, the extinction of the cluster due to interstellar dust is around 0.30.