NGC 381

NGC 381 is an open cluster of stars in the northern constellation of Cassiopeia, located at a distance of approximately 3,120 light-years from the Sun.^[2] Credit for the discovery of this cluster was given to Caroline Herschel by her brother William in 1787, although she may never have actually seen it.^[7]

NGC 381
Observation data (J2000 epoch)
Right ascension	01h 08m 19.9s[1]
Declination	+61° 35′ 02″[1]
Distance	3,120 ± 300 ly (957 ± 93 pc)[2]
Apparent magnitude (V)	9.3[3]
Apparent dimensions (V)	6′[1] or 7′[3]
Physical characteristics
Mass	32.4+45.2 −18.9[4] M☉
Radius	15 ly[5]
Estimated age	316+39 −34[2]
Other designations	Collinder 10[6]
Associations
Constellation	Cassiopeia[3]
See also: Open cluster, List of open clusters

This is a Trumpler class III 1 m cluster of intermediate age,^[1] estimated at 316 million years. This class indicates the cluster is relatively weakly concentrated, with a small brightness range and an intermediate richness of stars. A total of 350 probable members have been identified, down to 20th magnitude,^[2] and the cluster contains about 32 times the mass of the Sun.^[4] The cluster has a core angular radius of 2.99′±0.93′ and an outer cluster radius of 5.6′±0.1′.^[2] It has a physical tidal radius of 15 ly (4.7 pc).^[5] No giant stars have been discovered in this cluster.^[1] Four candidate variable stars have been found in the field of NGC 381; one of which is a suspected cluster member.^[8] The eclipsing binary OX Cassiopeiae was once thought to be a member, but is now known to be a background star system.^[9]