Messier 52 or M52, also known as NGC 7654, is an open cluster of stars in the highly northern constellation of Cassiopeia. It was discovered by Charles Messier on 1774.[3][a] It can be seen from Earth under a good night sky with binoculars. The brightness of the cluster is influenced by extinction, which is stronger in the southern half.[6] Its metallicity is somewhat below that of the Sun, and is estimated to be [Fe/H] = −0.05 ± 0.01.[7]
R. J. Trumpler classified the cluster appearance as II2r, indicating a rich cluster with little central concentration and a medium range in the brightness of the stars.[8] This was later revised to I2r, denoting a dense core.[6] The cluster has a core radius of 2.97 ± 0.46 ly (0.91 ± 0.14 pc) and a tidal radius of 42.7 ± 7.2 ly (13.1 ± 2.2 pc).[4] It has an estimated age of 158.5 million years[1] and a mass of 1,200 M☉.[4]
The magnitude 8.3 supergiant star BD +60°2532 is a probable member of the cluster,[4] so too 18 candidate slowly pulsating B stars, one being a Delta (δ) Scuti variable, and three candidate Gamma Doradus (γ Dor) variables.[9] There may also be three Be stars.[10] The core of the cluster shows a lack of interstellar matter, which may be due to supernovae explosion(s) early in the cluster's history.