Messier 71

Coordinates: Sky map 19h 53m 46.11s, +18° 46′ 42.3″
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Messier 71
Observation data (J2000 epoch)
Right ascension19h 53m 46.49s[1]
Declination+18° 46′ 45.1″[1]
Distance13.0 kly (4.0 kpc)[2]
Apparent magnitude (V)8.2[3]
Apparent dimensions (V)7.2'
Physical characteristics
Mass1.7×104[4] M
Radius13 ly[5]
Metallicity = –0.78[6] dex
Estimated age9-10 Gyr
Other designationsM71, NGC 6838, Cr 409, GCl 115[7]
See also: Globular cluster, List of globular clusters

Messier 71 (also known as M71 or NGC 6838) is a globular cluster in the small northern constellation Sagitta. It was discovered by Philippe Loys de Chéseaux in 1745 and included by Charles Messier in his catalog of non-comet-like objects in 1780. It was also noted by Koehler at Dresden around 1775.[8]

This star cluster is about 13,000 light years away from Earth and spans 27 light-years (8 pc). The irregular variable star Z Sagittae is a member.[9]

M71 was for many decades thought (until the 1970s) to be a densely packed open cluster and was classified as such by leading astronomers in the field of star cluster research due to its lacking a dense central compression, and to its stars having more "metals" than is usual for an ancient globular cluster; furthermore, it lacks the RR Lyrae "cluster" variable stars that are common in most globulars. However, modern photometric photometry has detected a short "horizontal branch" in the H-R diagram (chart of temperature versus luminosity) which is characteristic of a globular cluster. The shortness of the branch explains the lack of RR Lyrae variables and is due to the globular's relatively young age of 9–10 billion years. Taking in many or only late series (Population I) stars explains relatively its stars. Hence today M71 is designated as a very loosely concentrated globular cluster, much like M68 in Hydra. M71 has a mass of about 53,000 M and a luminosity of around 19,000 L.[10]

Map showing location of M71

See also[edit]


  1. ^ 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.
  2. ^ 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, S2CID 16914232.
  3. ^ "Messier 71". SEDS Messier Catalog. Retrieved 30 April 2022.
  4. ^ 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, S2CID 118652005. Mass is from MPD on Table 1.
  5. ^ distance × sin( diameter_angle / 2 ) = 13 ly. radius
  6. ^ 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.
  7. ^ "M 71". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-17.
  8. ^ "New General Catalog Objects: NGC 6800 - 6849". Retrieved 2021-03-11.
  9. ^ "Z Sge". The International Variable Star Index. AAVSO. Retrieved 1 March 2021.
  10. ^ Dalgleish, H.; Kamann, S.; Usher, C.; Baumgardt, H.; Bastian, N.; Veitch-Michaelis, J.; Bellini, A.; Martocchia, S.; Da Costa, G. S.; Mackey, D.; Bellstedt, S.; Pastorello, N.; Cerulo, P. (March 2020). "The WAGGS project-III. Discrepant mass-to-light ratios of Galactic globular clusters at high metallicity". Monthly Notices of the Royal Astronomical Society. 492 (3): 3859–3871. Bibcode:2020MNRAS.492.3859D. doi:10.1093/mnras/staa091.

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