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.[5][8] The cluster was discovered by French astronomer
Charles Messier on June 3, 1764, who described it as a "nebula without stars".[9] 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.[10]
At about 80' (1+1⁄3 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.
^Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin, 849 (849): 11–14,
Bibcode:
1927BHarO.849...11S.
^Klein, Hermann Joseph (1901),
Star Atlas, Society for promoting Christian knowledge, p. 55.
^Arellano Ferro, A.; et al. (September 2013), "A detailed census of variable stars in the globular cluster NGC 6333 (M9) from CCD differential photometry", Monthly Notices of the Royal Astronomical Society, 434 (2): 1220–1238,
arXiv:1306.3206,
Bibcode:
2013MNRAS.434.1220A,
doi:
10.1093/mnras/stt1080.