History

The Italian astronomer Giovanni Hodierna was probably the first to discover this star cluster in 1654. On 19 February 1771, Charles Messier came across the cluster, but noted the wrong coordinates, which is why it was later listed as NGC 2478 and turned out to be nonexistent. Caroline Herschel noticed the cluster in 1783 and her husband Wilhelm measured the position two years later on 4 February 1785, and the cluster was numbered NGC 2422 in Dreyer's NGC catalog. It was not until 1959 that it was noticed that Messier had miscalculated the position and he actually observed Herschel's NGC 2422.

Physical Properties

M 47 is an open star cluster with stars of 4th magnitude and the Trumpler classification III2m. It contains about 50 stars, which are spread over an area of about half a degree. Distance measurements range from 491 pc to 542 pc (1600 to 1768 light years). The estimated diameter is around 15 light years. The hottest star in the main sequence is of type B2. Most of the other stars are of type B and A. Two are orange stars. The stellar population is comparable to that of the Pleiades. The age of the cluster is estimated to be around 80 million years. ^{[4, 145, 196]}

A special treat is the double star STF 1121. It is not a double or multiple star, but forms the center of the open cluster. Stars A/B (6.9 mag, 7.3 mag, position angle 300°, distance 6.5"), star D (9.5 mag, 72", distance increasing), E (9.9 mag, 70", distance decreasing) and G (7.7 mag, 82").^[267]