Messier 103

Messier 103
Open cluster Messier 103 in Cassiopeia
Observation data (J2000.0 epoch)
Right ascension	01h 33.2m
Declination	+60° 42′
Distance	9,400 light-years (2.884 ± 0.313 kpc[1])
Apparent magnitude (V)	7.4[2]
Apparent dimensions (V)	6.0'
Physical characteristics
Estimated age	12.6 ± 0.2 million years[1]
Other designations	NGC 581, Cr 14
Associations
See also: Open cluster, List of open clusters

Messier 103 (also known as M103, or NGC 581) is a small open cluster of many faint stars in Cassiopeia. It was discovered on 27 March 1781 by Pierre Méchain, but later added as Charles Messier's last deep-sky object in his catalogue.^[3]

It is located 9,400 light-years from the Sun^[1][3] and is about 15 light years across. It holds two prominent stars, of which the brightest is magnitude 10.5, and in the center of the cluster, another magnitude 10.8 red giant. Another bright foreground object is the double star Struve 131,^[4] but is not a member of the cluster. Cluster membership is about 172 stars based on >50% probability of gravitational attachment that binds the cluster together.^[4] M103 is between 12.6^[1] to 25 million years^[5] in age.