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Messier 70
Globular cluster Messier 70 by Hubble Space Telescope; 3.3′ view
Observation data (J2000 epoch)
Class	V
Constellation	Sagittarius
Right ascension	18 43 12.76
Declination	–32° 17′ 31.6″
Distance	29.4 kly (9.0 kpc)
Apparent magnitude (V)	7.9
Apparent dimensions (V)	8.0′
Physical characteristics
Mass	1.79×10 M☉
Radius	34 ly
Tidal radius	11.2′
Metallicity	${\displaystyle {\begin{smallmatrix}\left\end{smallmatrix}}}$ = –1.35 dex
Estimated age	12.80 Gyr
Other designations	GCl 101, M70, NGC 6681
See also: Globular cluster, List of globular clusters

Messier 70 or M70, also known as NGC 6681, is a globular cluster of stars to be found in the south of Sagittarius. It was discovered by Charles Messier in 1780. The famous comet Hale–Bopp was discovered near this cluster in 1995.

It is about 29,400 light years away from Earth and around 6,500 light-years from the Galactic Center. It is roughly the same size and luminosity as its neighbour in space, M69. M70 has a very small core radius of 0.22 ly (0.068 pc) and a half-light radius of 182.0 ly (55.80 pc). This cluster has undergone core collapse, leaving it centrally concentrated with the luminosity distribution following a power law.

There are two distinct stellar populations in the cluster, with each displaying unique abundances. These likely represent different generations of stars. Five known variable stars lie within the broadest radius, the tidal radius, of it, all of which are RR Lyrae variables. The cluster may have two blue stragglers near the core.

Gallery

• Image by Hubble Space Telescope
• Map showing M70, against a conventional (southern) horizon

See also

• List of Messier objects

References and footnotes

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. 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. ^ "NGC 6681". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 17 November 2006.
4. ^ 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, S2CID 118649860.
5. "Messier 70". SEDS Messier Catalog. Retrieved 30 April 2022.
6. ^ Adam, Len (2018), Imaging the Messier Objects Remotely from Your Laptop, The Patrick Moore Practical Astronomy Series, Springer, p. 304, Bibcode:2018imor.book.....A, ISBN 978-3319653853
7. distance × sin( diameter_angle / 2 ) = 34 ly. radius
8. ^ Liller, M. H. (October 1983), "The variable stars in the field of the globular cluster NGC 6681", Astronomical Journal, 88: 1463–1469, Bibcode:1983AJ.....88.1463L, doi:10.1086/113435.
9. ^ 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.
10. Mobberley, Martin (2013), It Came From Outer Space Wearing an RAF Blazer!: A Fan's Biography of Sir Patrick Moore, Springer Science & Business Media, p. 483, ISBN 978-3319006093
11. ^ Watson, Alan M.; et al. (November 1994), "Far-ultraviolet imaging of the globular cluster NGC 6681 with WFPC2" (PDF), Astrophysical Journal, Part 2, 435 (1): L55–L58, Bibcode:1994ApJ...435L..55W, doi:10.1086/187593.{{citation}}: CS1 maint: multiple names: authors list (link)
12. Frommert, Hartmut; Kronberg, Christine (30 August 2007), "Globular Cluster M70", SEDS Messier pages, Students for the Exploration and Development of Space (SEDS), retrieved 4 December 2018.
13. Djorgovski, S. (January 1993), "Physical Parameters of Galactic Globular Clusters", in Djorgovski, S. G.; Meylan, G. (eds.), Structure and Dynamics of Globular Clusters. Proceedings of a Workshop held in Berkeley, California, July 15–17, 1992, to Honor the 65th Birthday of Ivan King, vol. 50, San Francisco, California: Astronomical Society of the Pacific, p. 373, Bibcode:1993ASPC...50..373D, ISBN 978-0937707692.
14. Forbes, Duncan A.; et al. (October 2008), "Uniting old stellar systems: from globular clusters to giant ellipticals", Monthly Notices of the Royal Astronomical Society, 389 (4): 1924–1936, arXiv:0806.1090, Bibcode:2008MNRAS.389.1924F, doi:10.1111/j.1365-2966.2008.13739.x, S2CID 14108457.
15. Pryor, Carlton; et al. (August 1989), "Mass-to-light ratios for globular clusters. I - The centrally concentrated clusters NGC 6624, M28 (NGC 6626), and M70 (NGC 6681)", Astronomical Journal, 98: 596–610, Bibcode:1989AJ.....98..596P, doi:10.1086/115160.
16. O'Malley, Erin M.; et al. (September 2017), "High-resolution Spectroscopic Abundances of Red Giant Branch Stars in NGC 6681", The Astrophysical Journal, 846 (1): 15, arXiv:1706.06962, Bibcode:2017ApJ...846...23O, doi:10.3847/1538-4357/aa7b72, S2CID 118972140, 23.
17. Clement, Christine M.; et al. (November 2001), "Variable Stars in Galactic Globular Clusters", The Astronomical Journal, 122 (5): 2587–2599, arXiv:astro-ph/0108024, Bibcode:2001AJ....122.2587C, doi:10.1086/323719, S2CID 38359010.

1. On the southernmost line of the main (teapot) asterism; its declination means it will not rise (above the horizon) above the 58th parallel north and will need the observer to be as much as a further fifteen degrees of latitude south for detailed, little distorted observation
2. on 31 August
3. on 23 July

External links

• Messier 70, Galactic Globular Clusters Database page
• Messier 70 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

• Astronomy
• Stars
• Outer space

v t e Messier objects
List	M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M13 M14 M15 M16 M17 M18 M19 M20 M21 M22 M23 M24 M25 M26 M27 M28 M29 M30 M31 M32 M33 M34 M35 M36 M37 M38 M39 M40 M41 M42 M43 M44 M45 M46 M47 M48 M49 M50 M51 M52 M53 M54 M55 M56 M57 M58 M59 M60 M61 M62 M63 M64 M65 M66 M67 M68 M69 M70 M71 M72 M73 M74 M75 M76 M77 M78 M79 M80 M81 M82 M83 M84 M85 M86 M87 M88 M89 M90 M91 M92 M93 M94 M95 M96 M97 M98 M99 M100 M101 M102 M103 Added M104 M105 M106 M107 M108 M109 M110
See also	Caldwell catalogue Catalogue of Nebulae and Clusters of Stars Herschel 400 Catalogue Index Catalogue New General Catalogue Revised New General Catalogue
Category Commons Portal

• Globular clusters
• Sagittarius (constellation)
• Messier objects
• NGC objects
• Astronomical objects discovered in 1780
• Discoveries by Charles Messier