Messier 12 or M 12 (also designated NGC 6218) is a globular cluster in the constellation of Ophiuchus. It was discovered by the French astronomer Charles Messier on May 30, 1764, who described it as a "nebula without stars".[8] In dark conditions this cluster can be faintly seen with a pair of binoculars. Resolving the stellar components requires a telescope with an aperture of 8 in (20 cm) or greater.[9] In a 10 in (25 cm) scope, the granular core shows a diameter of 3 (arcminutes) surrounded by a 10 halo of stars.[8]

Messier 12
M12 Adam Block.jpg
Globular cluster Messier 12 in Ophiuchus
Observation data (J2000 epoch)
ClassIX[1]
ConstellationOphiuchus
Right ascension16h 47m 14.18s[2]
Declination–01° 56′ 54.7″[2]
Distance16.44 ± 0.16 kly (5.04 ± 0.05 kpc)[3]
Apparent magnitude (V)6.7[4]
Apparent dimensions (V)16.0
Physical characteristics
Mass8.7×104[5] M
Radius37.2 ly[NB 1]
Metallicity = –1.14[6] dex
Estimated age13.8 ± 1.1 Gyr[3]
Other designationsNGC 6218[7]
See also: Globular cluster, List of globular clusters

Roughly 3°[9] northwest from the cluster M10 and 5.6° east southeast from star Lambda Ophiuchi, M12 is about 16,400 light-years (5,000 parsecs)[3] from Earth and has a spatial diameter of about 75 light-years. The brightest stars of M12 are of 12th magnitude. With a Shapley-Sawyer rating of IX,[1] it is rather loosely packed for a globular and was once thought to be a tightly concentrated open cluster. Thirteen variable stars have been recorded in this cluster. M12 is approaching us at a velocity of 16 km/s.[10]

A study published in 2006 concluded that this cluster has an unusually low number of low-mass stars. The authors surmise that they were stripped from the cluster by passage through the relatively matter-rich plane of the Milky Way.[11]

See alsoEdit

NotesEdit

  1. ^ distance × sin( diameter_angle / 2 ) = 37.2 ly radius

ReferencesEdit

  1. ^ a b 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. ^ a b c Gontcharov, George A.; Khovritchev, Maxim Yu; Mosenkov, Aleksandr V.; Il'In, Vladimir B.; Marchuk, Alexander A.; Savchenko, Sergey S.; Smirnov, Anton A.; Usachev, Pavel A.; Poliakov, Denis M. (2021). "Isochrone fitting of Galactic globular clusters – III. NGC 288, NGC 362, and NGC 6218 (M12)". Monthly Notices of the Royal Astronomical Society. 508 (2): 2688–2705. doi:10.1093/mnras/stab2756.
  4. ^ "Messier 12". SEDS Messier Catalog. Retrieved 27 April 2022.
  5. ^ Marks, Michael; Kroupa, Pavel (August 2010), "Initial conditions for globular clusters and assembly of the old globular cluster population of the Milky Way", Monthly Notices of the Royal Astronomical Society, 406 (3): 2000–2012, arXiv:1004.2255, Bibcode:2010MNRAS.406.2000M, doi:10.1111/j.1365-2966.2010.16813.x. Mass is from MPD on Table 1.
  6. ^ 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.
  7. ^ "M 12". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-15.
  8. ^ a b Thompson, Robert Bruce; Thompson, Barbara Fritchman (2007), Illustrated guide to astronomical wonders, DIY science O'Reilly Series, O'Reilly Media, Inc., p. 137, ISBN 978-0596526856.
  9. ^ a b Monks, Neale (2010), Go-To Telescopes Under Suburban Skies, Patrick Moore's Practical Astronomy Series, Springer, p. 118, ISBN 978-1441968500.
  10. ^ "Messier 12: Gumball Globular | Messier Objects". www.messier-objects.com. Retrieved 2015-08-17.
  11. ^ How to Steal a Million Stars?, ESO, February 7, 2006, archived from the original on February 8, 2007.

External linksEdit

Coordinates:   16h 47m 14.52s, −01° 56′ 52.1″