# Messier 2

Messier 2
Messier 2 by Hubble Space Telescope; 3.5′ view
Credit: NASA/STScI/WikiSky
Observation data (J2000 epoch)
Class II[1]
Constellation Aquarius
Right ascension 21h 33m 27.02s[2]
Declination –00° 49′ 23.7″[2]
Distance 33×103 ly (10 kpc)[3]
Apparent magnitude (V) +6.3[4]
Apparent dimensions (V) 16′.0
Physical characteristics
Mass 1.04×105[5] M
Metallicity ${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = –1.65[5] dex
Estimated age 13 Gyr
Other designations NGC 7089.[4]

Messier 2 or M2 (also designated NGC 7089) is a globular cluster in the constellation Aquarius, five degrees north of the star Beta Aquarii. It was discovered by Jean-Dominique Maraldi in 1746, and is one of the largest known globular clusters.

## Discovery and visibility

M2 was discovered by the French astronomer Jean-Dominique Maraldi in 1746 while observing a comet with Jacques Cassini. Charles Messier rediscovered it in 1760, but thought it a nebula without any stars associated with it. William Herschel, in 1783, was the first to resolve individual stars in the cluster.

M2 is, under extremely good conditions, just visible to the naked eye. Binoculars or a small telescope will identify this cluster as non-stellar, while larger telescopes will resolve individual stars, of which the brightest are of apparent magnitude 13.1.

## Characteristics

M2 is about 37,500 light-years distant from Earth. At 175 light-years in diameter, it is one of the larger globular clusters known. The cluster is rich, compact, and significantly elliptical. It is 13 billion years old and one of the older globulars associated with the Milky Way Galaxy.

M2 contains about 150,000 stars, including 21 known variable stars. Its brightest stars are red and yellow giant stars. The overall spectral type is F4.[4]

## References

1. ^ Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin (849): 11–14, Bibcode:1927BHarO.849...11S.
2. ^ a b 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:1008.2755, Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830.
3. ^ Hessels, J. W. T.; et al. (November 2007), "A 1.4 GHz Arecibo Survey for Pulsars in Globular Clusters", The Astrophysical Journal, 670 (1): 363–378, arXiv:0707.1602, Bibcode:2007ApJ...670..363H, doi:10.1086/521780
4. ^ a b c "SIMBAD Astronomical Object Database". Results for NGC 7089. Retrieved 2006-11-15.
5. ^ a b Boyles, J.; et al. (November 2011), "Young Radio Pulsars in Galactic Globular Clusters", The Astrophysical Journal, 742 (1): 51, arXiv:1108.4402, Bibcode:2011ApJ...742...51B, doi:10.1088/0004-637X/742/1/51.
6. ^ distance × sin( diameter_angle / 2 ) = 87.3 ly. radius