Messier 9

Messier 9 or M9 (also designated NGC 6333) is a globular cluster in the constellation of Ophiuchus. It is positioned in the southern part of the constellation to the southwest of Eta Ophiuchi, and lies atop a dark cloud of dust designated Barnard 64.<ref name="Gilmour2012"/><ref name="OMeara2014"/> The cluster was discovered by French astronomer Charles Messier on June 3, 1764, who described it as a "nebula without stars".<ref name="Machholz2002"/> In 1783, English astronomer William Herschel was able to use his reflector to resolve individual stars within the cluster. He estimated the cluster to be 7–8′ in diameter with stars densely packed near the center.<ref name="Klein1901"/>

M9 has an apparent magnitude of 7.9, an angular size of 9.3′, and can be viewed with a small telescope.<ref name="Gilmour2012"/> It is one of the nearer globular clusters to the center of the galaxy as is around 5,500 light-years from the Galactic Center. Its distance from Earth is 25,800 light-years.

The total luminosity of this cluster is around 120,000 times that of the Sun, the absolute magnitude being -8.04. The brightest individual stars in M9 are of apparent magnitude 13.5, making them visible in moderately sized telescopes. There have been 24 variable stars found in M9: 21 RR Lyrae variables, plus a long-period variable, Type II Cepheid, and an eclipsing binary. No blue stragglers or SX Phoenicis variables have been discovered. Based upon the periods of the RR Lyr variables, this cluster is classified as an Oosterhoff type II globular, which precludes an extra-galactic origin.<ref name=mnras434_2_1220/>

At about 80' (Template:Frac degrees) to the northeast of M9 is the dimmer globular cluster NGC 6356, while about the same to the southeast is the globular NGC 6342.

Gallery

• Messier object 009.jpg

  Messier 9, from 2MASS

• M9map.png

  Map showing the location of Messier 9

See also

• List of Messier objects

External links

• Messier 9, SEDS Messier pages
• M9, Galactic Globular Clusters Database page
• The glittering stars of Messier 9, March 16, 2012, Tg Daily Staff, TG Daily
• Template:APOD
• Template:WikiSky

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