# Messier 69

Messier 69
M69 by Hubble Space Telescope; 3.5′ view
Credit: NASA/STScI/WikiSky
Observation data (J2000 epoch)
ClassV[1]
ConstellationSagittarius
Right ascension 18h 31m 23.10s[2]
Declination−32° 20′ 53.1″[2]
Distance29 kly (8.8 kpc)[3]
Apparent magnitude (V)+8.31[4]
Apparent dimensions (V)10′.8[3]
Physical characteristics
Mass2.0×105 M[5] M
Metallicity${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = –0.78[7] dex
Estimated age13.06 Gyr[7]
Other designationsGCl 96, M69, NGC 6637[4]

Messier 69 or M69, also known NGC 6637, is a globular cluster in the southern constellation of Sagittarius. It can be found 2.5° to the northeast of the star Epsilon Sagittarii and is dimly visible in 50 mm aperture binoculars. The cluster was discovered by Charles Messier on August 31, 1780, the same night he discovered M70. At the time, he was searching for an object described by Nicolas-Louis de Lacaille in 1751–2 and thought he had rediscovered it, but it is unclear if Nicolas-Louis de Lacaille actually described M69.[8]

This cluster is at a distance of about 28,700[3] light-years away from Earth and 5,200 ly from the Galactic Center,[9] with a spatial radius of 45 light-years.[6] It is a relatively metal-rich globular cluster that is a likely member of the Galactic bulge population.[10] M69 has a mass of 2.0×105 M with a half-mass radius of 11.6 ly,[5] a core radius of 29.2 ly, and a tidal radius of 91.9 ly.[3] The center of the cluster has a luminosity density of 6,460 L·pc−3.[9] It is a close neighbor of globular cluster M70, with perhaps only 1,800 light-years separating the two objects.[11]

## References

1. ^ Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin, 849 (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. Kharchenko, N. V.; et al. (2013), "Global survey of star clusters in the Milky Way. II. The catalogue of basic parameters", Astronomy and Astrophysics, 558: 8, arXiv:1308.5822, Bibcode:2013A&A...558A..53K, doi:10.1051/0004-6361/201322302, A53.
4. ^ a b "NGC 6637". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-17.
5. ^ a b Mandushev, G.; et al. (December 1991), "Dynamical masses for galactic globular clusters", Astronomy and Astrophysics, 252: 94, Bibcode:1991A&A...252...94M.
6. ^ a b From trigonometry: distance × sin( diameter_angle / 2 ) = 28,700 × 0.00157 = 45 ly. radius
7. ^ a b 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:1001.4289, Bibcode:2010MNRAS.404.1203F, doi:10.1111/j.1365-2966.2010.16373.x.
8. ^ Thompson, Robert Bruce; Thompson, Barbara Fritchman (2007), Illustrated Guide to Astronomical Wonders: From Novice to Master Observer, Maker Media, Inc., ISBN 978-1680451917
9. ^ a b Piotto, G.; et al. (September 2002), "HST color-magnitude diagrams of 74 galactic globular clusters in the HST F439W and F555W bands", Astronomy and Astrophysics, 391 (3): 945–965, arXiv:astro-ph/0207124, Bibcode:2002A&A...391..945P, doi:10.1051/0004-6361:20020820.
10. ^ Heasley, J. N.; et al. (August 2000), "Hubble Space Telescope Photometry of the Metal-rich Globular Clusters NGC 6624 and NGC 6637", The Astronomical Journal, 120 (2): 879–893, Bibcode:2000AJ....120..879H, doi:10.1086/301461.
11. ^ Frommert, Hartmut; Kronberg, Christine (July 20, 2011), "Globular Cluster M69", SEDS Messier pages, Students for the Exploration and Development of Space (SEDS), retrieved 2018-12-03.
12. ^ "Cosmic riches". ESA/Hubble Picture of the Week. Retrieved 3 October 2012.