Messier 23

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Messier 23
M23 Eguivar.jpg
Open cluster Messier 23 in Sagittarius
Observation data (J2000 epoch)
Right ascension 17h 57m 04s [1]
Declination −18° 59 06
Distance 2,050  ly (628  pc) [2]
Apparent magnitude  (V)5.5 [3]
Apparent dimensions (V)35 [2]
Physical characteristics
Mass1,206 [4]   M
Radius8 ly
Estimated age330±100 myr [5]
Other designations M23, NGC 6494, [6] Cr 356, C 1753-190
Associations
Constellation Sagittarius
See also: Open cluster, List of open clusters

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. [lower-alpha 1] [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]

Contents

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, [lower-alpha 2] 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]

See also

Footnotes and References

Footnotes

  1. On June 20
  2. east of blue-white 7th magnitude fellow member HD 163427

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References

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