Messier 23

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Messier 23, also known as NGC 6494, is an open cluster of stars in the northwest of the southern constellation of Sagittarius.<ref name=Gilmour2003/> It was discovered by Charles Messier in 1764.Template:Efn<ref name=Thompson2007/> It can be found in good conditions with binoculars or a modestly sized telescope.<ref name=Thompson2007/> It is in front of "an extensive gas and dust network", which there may be no inter-association.<ref name=McNamara1983/> It is within 5° the sun's position (namely in mid-December) so can be occulted by the moon.<ref name=Ridgway1979/>

The cluster is centered about 2,050 light years away. Estimates for the number of its members range from 169<ref name=Sanders1980/> up to 414, with a directly-counted mass of Template:Val; Template:Val by application of the virial theorem.<ref name=McNamara1983/> The cluster is around 330 million years old with a near-solar metallicity of [Fe/H] = −0.04.<ref name=netopil2016/> The brightest component (lucida) is of magnitude 9.3.<ref name=Sanders1990/> Five of the cluster members are candidate red giants,<ref name=Claria1989/> while orange variable VV Sgr in the far south,Template:Efn is a candidate asymptotic giant branch star.<ref name=Jura1987/>

A 6th-magnitude star, shown in the top-right corner, figures in the far north-west as a foreground star – HD 163245 (HR 6679). Its parallax shift is Template:Val, having taken into account proper motion, which means it is about Template:Convert away.<ref>Template:Cite Gaia DR2</ref>