Globular Cluster Messier 9
Messier 9 is a small, bright globular cluster and was discovered in 1764 together with M 10, M 12 and M 14 within a few nights. M 9 is the smallest cluster of this quartet. The most striking feature is its slightly oval shape and a small curved chain of six stars southwest of the center (see fig. 1). At the moment it is not known to the author whether this star chain belongs to M 9 or is only in the foreground.
M 9 is relatively close to the central bulge of the Milky Way system. The calculated distance is given as about 7500 light years. For comparison: the sun is around 26'000 light years away from the galactic center. The diameter of M 9 is around 60 light years and the total luminosity is estimated to be 60'000 times that of the sun, if one can assume that around half of the light is absorbed by interstellar matter in between. Strong absorption in the north and west suggests that the light is weakened by at least about one magnitude. Not surprising, since the sharply delimited dark cloud B 62, which appears to be part of a larger complex of interstellar matter, is located close to M 9 in a south-westerly direction. The globular cluster moves away from us at a radial speed of about 225 km/s. 
|Right Ascension||17h 19m 11.8s|
|Declination||-18° 30' 57"|
|Visual magnitude||7.8 mag|
|Metric Distance||7.900 kpc|
|Dreyer Description||globular, B, L, R, eCM, rrr, st 14|
|Identification, Remarks||M 9, GCL 60, ESO 587-SC5|
The globular cluster Messier 9 is located in the constellation Serpent Bearer (Ophiuchus), roughly in the middle between the 2.43 mag bright star Sabik (η Ophiuchi) and the 4.39 mag bright star ξ Ophiuchi. It is best seen between May and July.