|Right Ascension||15 : 18.6 (h:m)
|Declination||+02 : 05 (deg:m)
|Visual Brightness||5.6 (mag)
|Apparent Dimension||17.4 (arc min)
Discovered 1702 by Gottfried Kirch.
Globular cluster M5 was first seen by Gottfried Kirch and his wife Maria Margarethe on May 5, 1702, when they observed a comet, and described as a "nebulous star". Charles Messier found it on May 23, 1764, and describes it as a round nebula which "doesn't contain any stars". William Herschel was the first to resolve this cluster into stars; he counted 200 of them with his 40-foot [FL] reflector in 1791, "although the middle is so compressed that it is impossible to distinguish the components".
M5 shows a distinct ellipticity, elongated at position angle 50 degrees (position angles give the orientation of a feature in the celestial sphere; they are measured between North and the direction considered, in counterclockwise sense); it is thought to be one of the oldest globular clusters, with a computed age of 13 billion years. Its diameter is about 140 light years, making it one of the larger globular clusters. At its distance of 24,500 light years, this diameter is about 17 minutes of arc. M5 is receding from us at about 50 km/sec.
M5 contains the considerably large number of 105 known variable stars. The first variables in this cluster were noted by A.A. Common in 1890. S.I. Bailey (1899) found 85 short-period variables in this cluster, of type RR Lyrae (or cluster variables); 97 of them were known in 1955, according to Kenneth Glyn Jones. One of the other variables is a dwarf nova, according to Cecilia Payne-Gaposhkin.
Our image of M5 was obtained (and is copyrighted) by David Malin of the Anglo Australian Observatory. More information on this image is available.
Further informations and interesting details on M5 can be found Leos Ondra's article `Messier 5 and its Variables'. Thanks to Leos for allowing to include his article in this page ! It includes, among other interesting stuff, a Color-Magnitude Diagram of M5.
Near M5 is the bright double star 5 Serpentis (Struve 1930) with components A, 5 mag, pale yellow, and B, 10 mag, light grey; position angle 37 deg, distance 11" (as determined in 1923). This star is mentioned in Messier's description (but not its character as double).
Last Modification: 9 Dec 1999, 22:58 MET