Messier 9 orM9 (also designatedNGC 6333) is aglobular cluster in theconstellation ofOphiuchus. It is positioned in the southern part of the constellation to the southwest ofEta Ophiuchi, and lies atop a dark cloud of dust designated Barnard 64.[5][8] The cluster was discovered by French astronomerCharles Messier on June 3, 1764, who described it as a "nebula without stars".[9] In 1783, English astronomerWilliam 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 clusterNGC 6356, while about the same to the southeast is the globularNGC 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.
