|Observation data: 2000.0 epoch|
|Right ascension||21h 33m|
|Distance||37.500 light years|
|Diameter in ly||174 light years|
|Other designations||Messier 2|
Discovery and Observational data
NGC 7089 was first discovered in 1746 by Jean-Dominique Maraldi. French comet hunter Charles Messier included the cluster on his list of nebulous objects in 1760 as the second entry after the Crab Nebula. Messier was unable to resolve the cluster into individual stars and thus called it a "nebula". It was William Herschel who first discovered the true identity of the cluster when he resolved individual stars.
Messier 2 can be found less than 5° almost due north of β Aqr. and shines with an apparent magnitude of 6.5, placing it below naked-eye visibility. It is however, easily seen with binoculars or modest amateur telescopes. Larger telescopes are needed to fully resolve the golular into stars.
NGC 7089 is a rather compact globular cluster of type II and is decidedly elliptical in shape. The cluster has a diameter of about 175 light years and is some 37.500 light years distant. The brightest individual stars of NGC 7089 are of apparent magnitude +13.1 while the estimated age of the cluster is in the order of 13 X 109 years. The absolute magnitude for NGC 7089 is -9.0.
The half-mass radius of NGC 7089, ie the distance from the center of the cluster where half of the object's mass is concentrated, is 10 light years while the tidal radius, the point at which the gravitational influence of the cluster falls below that of the Milky Way as a whole, is about 233 light years from the center of the cluster. Stars beyond this distance would escape the cluster's gravitational pull. The overall spectraltype of NGC 7089 is F4.
Messier 2 follows a highly elongated (e=0.76) orbit around the Milky Way Galaxy taking it from between 23.500 light years to up to about 171.000 light years from the galaxtic center.
Like many globular clusters, NGC 7089 contains a number of variable stars, most notable of the RR Lyrae type. There are also 3 W Virginis Cepheid type variables known within this object as well as an RV Tauri star. The first of these variable stars within Messier 2 were discovered in 1895 by Solon Bailey.
- William E. Harris, Catalog Of Parameters For Milky Way Globular Clusters, February 2003, online at: http://www.physics.mcmaster.ca/~harris/mwgc.dat
- Brosche et al, Space Motions and Orbits of Globular Clusters, 1997