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.[1] It was discovered by Charles Messier in 1764.Template:Efn[2] It can be found in good conditions with binoculars or a modestly sized telescope.[2] It is in front of "an extensive gas and dust network", which there may be no inter-association.[3] It is within 5° the sun's position (namely in mid-December) so can be occulted by the moon.[4]
The cluster is centered about 2,050 light years away. Estimates for the number of its members range from 169[5] up to 414, with a directly-counted mass of Template:Val; Template:Val by application of the virial theorem.[3] The cluster is around 330 million years old with a near-solar metallicity of [Fe/H] = −0.04.[6] The brightest component (lucida) is of magnitude 9.3.[7] Five of the cluster members are candidate red giants,[8] while orange variable VV Sgr in the far south,Template:Efn is a candidate asymptotic giant branch star.[9]
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.[10]
Gallery
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Map showing the location of M23
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Open cluster Messier 23 in Sagittarius
See also
Footnotes and References
Footnotes
References
External links
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<ref>tag; no text was provided for refs namedJura1987 - ↑ Template:Cite Gaia DR2