NGC 1981

NGC 1981 (Upper Sword) is an open cluster in the constellation of Orion, found north of the nebula NGC 1977 (Running Man). It is 1.300 light-years away and it was discovered by John Herschel in 1827. It is quite easy to see the cluster with the naked eye, having an apparent magnitude of +4,2.

The cluster has young B-type stars, 5-10 million years old. These are embedded in the Orion Nebula Complex, in which they gradually erode away the gas due to their intense ultraviolet radiation. Also, it is one of the few clusters where there’s no evolved star, leaving the main sequence.