|Observation data (J2000 epoch)|
|Right ascension||15h 18m 33.22s|
|Declination||+02° 04′ 51.7″|
|Distance||24.5 kly (7.5 kpc)|
|Apparent magnitude (V)||+6.65|
|Apparent dimensions (V)||23′.0|
|Metallicity||= –1.12 dex|
|Estimated age||10.62 Gyr|
|Other designations||NGC 5904, GCl 34|
|Wikimedia Commons has media related to Messier 5.|
Discovery and visibility
M5 is, under extremely good conditions, just visible to the naked eye as a faint "star" near the star 5 Serpentis. Binoculars or small telescopes will identify the object as non-stellar while larger telescopes will show some individual stars, of which the brightest are of apparent magnitude 12.2.
M5 was discovered by German astronomer Gottfried Kirch in 1702 when he was observing a comet. Charles Messier also noted it in 1764, but thought it was a nebula without any stars associated with it. William Herschel was the first to resolve individual stars in the cluster in 1791, counting roughly 200.
Spanning 165 light-years in diameter, M5 is one of the largest known globular clusters. The gravitational sphere of influence of M5, (i.e. the volume of space in which stars are gravitationally bound to it rather than being torn away by the Milky Way's gravitational pull) has a radius of some 200 light-years.
At 13 billion years old, M5 is also one of the eldest globular clusters in the Milky Way Galaxy. Its distance is about 24,500 light-years from Earth, and it contains more than 100,000 stars, as many as 500,000 according to some estimates.
105 stars in M5 are known to be variable in brightness, 97 of them belonging to the RR Lyrae type. RR Lyrae stars, sometimes referred to as "Cluster Variables", are somewhat similar to Cepheid type variables and as such can be used as a tool to measure distances in outer space since the relation between their luminosities and periods are well known. The brightest and most easily observed variable in M5 varies from magnitude 10.6 to 12.1 in a period of just under 26.5 days.
A dwarf nova has also been observed in this cluster.
- Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin (849): 11–14, Bibcode:1927BHarO.849...11S.
- Goldsbury, Ryan; et al. (December 2010), "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters", The Astronomical Journal, 140 (6): 1830–1837, arXiv: , Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830.
- Paust, Nathaniel E. Q.; et al. (February 2010), "The ACS Survey of Galactic Globular Clusters. VIII. Effects of Environment on Globular Cluster Global Mass Functions", The Astronomical Journal, 139 (2): 476–491, Bibcode:2010AJ....139..476P, doi:10.1088/0004-6256/139/2/476.
- "M 5". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-15.
- Boyles, J.; et al. (November 2011), "Young Radio Pulsars in Galactic Globular Clusters", The Astrophysical Journal, 742 (1): 51, arXiv: , Bibcode:2011ApJ...742...51B, doi:10.1088/0004-637X/742/1/51.
- Forbes, Duncan A.; Bridges, Terry (May 2010), "Accreted versus in situ Milky Way globular clusters", Monthly Notices of the Royal Astronomical Society, 404 (3): 1203–1214, arXiv: , Bibcode:2010MNRAS.404.1203F, doi:10.1111/j.1365-2966.2010.16373.x.
- SIMBAD: M5
- M5,SEDS Messier pages
- M5, Galactic Globular Clusters Database page
- Historic observations of M5
- Image of M5 by Waid Observatory
- Messier 5 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images