Messier 93 orM93, also known asNGC 2447 or theCritter Cluster, is anopen cluster in the modestly southernconstellationPuppis, the imagined poop deck of the legendaryArgo.
It was discovered byCharles Messier then added to his catalogue ofcomet-like objects in 1781.[a][6]Caroline Herschel, the younger sister ofWilliam Herschel, independently discovered it in 1783, thinking it had not yet been catalogued by Messier.[7]
Some observers mention the cluster as having the shape of a starfish. With a fair-sized telescope, this is its appearance on a dull night, but [a four-inch refractor] shows it as a typical star-studded galactic cluster.
It has aTrumpler class ofI 3 r, indicating it is strongly concentrated (I) with a large range in brightness (3) and is rich in stars (r).[9]
M93 is about 3,380[1]light-years from thesolar radius and has a great spatial radius of 10 light-years,[3] atidal radius of13.1±2.3 ly,[4] and a core radius of 4.2 ly.[10] Its age is estimated at 387.3 million years.[1] It is nearly on thegalactic plane and has an orbit that varies between 28–29 kly (8.5–8.9 kpc) from theGalactic Center over a period of242.7±7.9 Myr.[1]
^Frommert, Hartmut; Kronberg, Christine (September 2, 2007),"Messier 93",SEDS Messier pages, Students for the Exploration and Development of Space (SEDS), retrieved2018-12-07.
^Maitzen, H. M. (November 1993), "Photoelectric Search for Peculiar Stars in Open Clusters - Part Fourteen - NGC1901 NGC2169 NGC2343 CR:132 NGC2423 and NGC2447",Astronomy and Astrophysics Supplement,102 (1): 1,Bibcode:1993A&AS..102....1M.
^Eyer, L.; Eggenberger, P.; Greco, C.; Saesen, S.; Anderson, R. I.; Mowlavi, N. (September 2010), "Time resolved surveys of stellar clusters",JENAM 2010, Joint European and National Astronomy Meeting held 6-10 September, 2010 in Lisbon Portugal, p. 212,arXiv:1011.4952,Bibcode:2010jena.confE.212E, 212.
^da Silveira, M. D.; et al. (June 2018), "Red giants and yellow stragglers in the young open cluster NGC 2447",Monthly Notices of the Royal Astronomical Society,476 (4):4907–4931,Bibcode:2018MNRAS.476.4907D,doi:10.1093/mnras/sty265
