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Messier 23
Open cluster in Sagittarius From Wikipedia, the free encyclopedia
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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.[7] It was discovered by Charles Messier in 1764.[a][3] It can be found in good conditions with binoculars or a modestly sized telescope.[3] It is in front of "an extensive gas and dust network", which there may be no inter-association.[4] It is within 5° the sun's position (namely in mid-December) so can be occulted by the moon.[8]
The cluster is centered about 2,050 light years away. Estimates for the number of its members range from 169[9] up to 414, with a directly-counted mass of 1,206 M☉; 1,332 M☉ by application of the virial theorem.[4] The cluster is around 330 million years old with a near-solar metallicity of [Fe/H] = −0.04.[5] The brightest component (lucida) is of magnitude 9.3.[10] Five of the cluster members are candidate red giants,[11] while orange variable VV Sgr in the far south,[b] is a candidate asymptotic giant branch star.[12]
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 9.8912±0.0518 mas, having taken into account proper motion, which means it is about 101 parsecs (330 ly) away.[13]
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Gallery
Map showing the location of M23
Open cluster Messier 23 in Sagittarius
See also
Footnotes and References
External links
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