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Melotte 20, The Alpha Persei Association
Melotte 20
Exposure Data
  • Image Field of View: 5.91° x 3.95°
  • Camera Field of View: 6.87° x 4.58°
  • Lens: Nikkor 180 mm f/2.8 ED AIS
  • Focal Length: 180 mm
  • Focal Ratio: f/3.2
  • Exposure: (45 minutes total)
    • 3 x 300 seconds
    • 3 x 600 seconds
  • Camera: Canon T4i (650D)
  • ISO: 800
  • Filter: IDAS LPS
  • SQM: 21.81

Melotte 20, the Alpha Persei Cluster, is a large, loose, open cluster in the constellation of Perseus. Mel 20 is also called the Alpha Persei Moving Cluster. The cluster spans most of the top and center of the image.

Mirfak (Alpha Persei) a yellow supergiant F-class star is the brightest member of the cluster and the brightest star in this image at top center, shining at magnitude 1.79. Psi Persei is the bright star at lower left, and Iota Persei is the bright star at the top right edge of the image.

Located at a distance of 600 light-years, the Alpha Persei Cluster shines at magnitude 1.2 and has an apparent size of 3 degrees. It is estimated to be 50 million to 70 million years old. It is a wonderful object in binoculars.

Other members of the cluster include Delta, Epsilon, Psi, 29, 30, 34 and 48 Persei, most of which are hot, young massive blue stars.

Open cluster NGC 1245 is also located at the bottom right of the frame in this image. It has an apparent diameter of 10 arcminutes and an apparent magnitude of 8.4.

The Alpha Persei cluster was first listed as a nebulous object by Hodierna and later cataloged by Melotte in 1915 as a star cluster.

North is to the top in the above image.

Melotte 20
  • Catalogs: Mel 20, Cr 39
  • Common Name: Alpha Persei Cluster
  • Object Type: Stellar Association
  • Magnitude: 1.2
  • Size: 180'
  • Constellation: Perseus
  • Image Field Centered At:
    • RA: 03h 27m 07s
    • Dec: +48° 50' 30"

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