Messier 71

Messier 71

Messier 71
M71 from Hubble Space Telescope; 3.35′ view
Credit: NASA/STScI/WikiSky
Observation data (J2000 epoch)
Class X-XI
Constellation Sagitta
Right ascension 19h 53m 46.49s[1]
Declination +18° 46′ 45.1″[1]
Distance 13.0 kly (4.0 kpc)[2]
Apparent magnitude (V) +6.1[3]
Apparent dimensions (V) 7′.2
Physical characteristics
Mass 1.7×104[4] M
Radius 13 ly[5]
Metallicity –0.78[6] dex
Estimated age 9-10 Gyr
Other designations M71, NGC 6838, GCl 115[3]

Messier 71 (also known as M71 or NGC 6838) is a globular cluster in the constellation Sagitta. It was discovered by Philippe Loys de Chéseaux in 1746 and included by Charles Messier in his catalog of comet-like objects in 1780. It was also noted by Koehler at Dresden around 1775.

M71 is at a distance of about 12,000 light years away from Earth and spans some 27 light years across. The irregular variable star Z Sagittae is a member of this cluster.

M71 was long 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 of M71, which is characteristic of a globular cluster. The shortness of the branch explains the lacking of the RR Lyrae variables and is due to the globular's relatively young age of 9-10 billion years. The relative youth of this globular also explains the abundance of "metals" in its stars. Hence today M71 is designated as a very loosely concentrated globular cluster, much like M68 in Hydra. M71 has a luminosity of around 13,200 Suns.

Map showing location of M71


  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,  
  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,  
  3. ^ a b "SIMBAD Astronomical Database". Results for NGC 6838. Retrieved 2006-11-17. 
  4. ^ Marks, Michael; Kroupa, Pavel (August 2010), "Initial conditions for globular clusters and assembly of the old globular cluster population of the Milky Way",   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,  

External links

  • Messier 71 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
  • Messier71 @ SEDS Messier pages
  • Messier 71, Galactic Globular Clusters Database page
  • Messier 71, LRGB CCD image based on two hours total exposure
  • Messier 71: an Unusual Globular Cluster, ESA\Hubble picture of the week.
  • McCormac, James;