Messier 5
From Wikipedia, the free encyclopedia
| M5 | |
 |
|
| Observation data (J2000 epoch) | |
|---|---|
| Class | V |
| Constellation | Serpens |
| Right ascension | 15h 18m 33.75s[1] |
| Declination | +02° 04′ 57.7″[1] |
| Distance | 24.5 kly (7.5 kpc) |
| Apparent magnitude (V) | +6.65[1] |
| Apparent dimensions (V) | 23′.0 |
| Physical characteristics | |
| Mass | kg ( M ) |
| Radius | 80 ly |
| Estimated age | 13 Gyr |
| Other designations | NGC 5904[1] |
| See also: Globular cluster, List of globular clusters | |
Globular Cluster M5 (also known as Messier Object 5 or NGC 5904) is a globular cluster in the constellation Serpens. It was discovered by Gottfried Kirch in 1702.
[edit] 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 this cluster as non-stellar while larger telescopes will start to show individual stars, of which the brightest are of apparent magnitude 12.2.
M5 was discovered by the German astronomer Gottfried Kirch in 1702 when he was observing a comet. Charles Messier found it in 1764 and thought it a nebula without any stars associated with it. William Herschel resolved individual stars in the cluster in 1791, counting roughly 200 of them.
M5 is not to be confused with the much fainter and more distant globular Palomar 5 which is situated nearby in the sky.
[edit] Scientific data
Spanning 165 light-years across, M5 is one of the larger globular clusters known. The gravitational sphere of influence of M5, (ie. the volume of space where stars would be gravitationally bound to the cluster and not ripped away from it by the Milky Way's gravitational pull), has a radius of some 200 light-years.
At 13 billion years old it is also one of the older globulars associated with the Milky Way Galaxy. The distance of M5 is about 24,500 light-years away from Earth and the cluster contains more than 100,000 stars up to perhaps 500,000 according to some estimates.
[edit] Variable stars
Some 105 stars in M5 are known to be variable in brightness, some 97 of them are of 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.
