Messier 93

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Messier 93 or M93, also known as NGC 2447 or the Critter Cluster, is an open cluster in the modestly southern constellation Puppis, the imagined poop deck of the legendary Argo.

Observational history and appearanceEdit

It was discovered by Charles Messier then added to his catalogue of comet-like objects in 1781.Template:Efn<ref name=Frommert2007/> Caroline Herschel, the younger sister of William Herschel, independently discovered it in 1783, thinking it had not yet been catalogued by Messier.<ref name=Hoskin2016/>

Walter Scott Houston (died 1993) described its appearance:<ref name="WSH"/>

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.

PropertiesEdit

It has a Trumpler class of Template:Nowrap, indicating it is strongly concentrated (I) with a large range in brightness (3) and is rich in stars (r).<ref name=Maitzen1993/>

M93 is about 3,380<ref name=Wu2009/> light-years from the solar radius and has a great spatial radius of 10 light-years,<ref name=Finlay2014/> a tidal radius of Template:Val,<ref name=Piskunov2008/> and a core radius of Template:Cvt.<ref name=Piskunov2007/> Its age is estimated at 387.3 million years.<ref name=Wu2009/> It is nearly on the galactic plane and has an orbit that varies between Template:Cvt from the Galactic Center over a period of Template:Val Myr.<ref name=Wu2009/>

Fifty-four variable stars have been found in M93, including one slowly pulsating B-type star, one rotating ellipsoidal variable, seven Delta Scuti variables, six Gamma Doradus variables, and one hybrid δTemplate:Efn Sct/γ DorTemplate:Efn pulsator.<ref name=Eyer2010/> Four spectroscopic binary systems within include a yellow straggler component.<ref name=Silveira2018/>