Messier 69

Coordinates: Sky map 18h 31m 23.23s, −32° 20′ 52.7″
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Messier 69
Globular cluster Messier 69 by Hubble Space Telescope; 3.5 view
Credit: NASA/STScI/WikiSky
Observation data (J2000 epoch)
Right ascension18h 31m 23.10s[2]
Declination−32° 20′ 53.1″[2]
Distance29 kly (8.8 kpc)[3]
Apparent magnitude (V)7.6[4]
Apparent dimensions (V)10.8[3]
Physical characteristics
Mass2.0×105 M[5] M
Radius45 ly[6]
Tidal radius91.9 ly.[3]
Metallicity = –0.78[7] dex
Estimated age13.06 Gyr[7]
Other designationsGCl 96, M69, NGC 6637[8]
See also: Globular cluster, List of globular clusters

Messier 69 or M69, also known NGC 6637, is a globular cluster in the southern constellation of Sagittarius.[a] 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 Lacaille actually described M69.[9]

This cluster is about 28,700[3] light-years away from Earth and 5,200 ly from the Galactic Center,[10] 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.[11] It has a mass of 200000 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] Its center has a bright luminosity density of 6,460 L·pc−3 (meaning per cubic parsec).[10] It is a close neighbor of its analog M70 – possibly only 1,800 light-years separates the two.[12]


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References and footnotes[edit]

  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, S2CID 119183070.
  3. ^ a b c d e 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, S2CID 118548517, A53.
  4. ^ "Messier 69". SEDS Messier Catalog. Retrieved April 30, 2022.
  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, S2CID 51825384.
  8. ^ "NGC 6637". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved November 17, 2006.
  9. ^ Thompson, Robert Bruce; Thompson, Barbara Fritchman (2007), Illustrated Guide to Astronomical Wonders: From Novice to Master Observer, Maker Media, Inc., ISBN 978-1680451917
  10. ^ 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, S2CID 17333985.
  11. ^ 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.
  12. ^ Frommert, Hartmut; Kronberg, Christine (July 20, 2011), "Globular Cluster M69", SEDS Messier pages, Students for the Exploration and Development of Space (SEDS), retrieved December 3, 2018.
  13. ^ "Cosmic riches". ESA/Hubble Picture of the Week. Retrieved October 3, 2012.
  1. ^ In daily rising of this globular cluster, whether in day- or nighttime, it will reach 15° above the due southern horizon, at the 90°−32°−15° parallel thus the 43rd parallel north, the furthest north for very detailed, easy observation for this object

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