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

Messier 71
M71 from w:Hubble Space Telescope; 3.35′ view
Credit: w:NASA/w:STScI/w:WikiSky
Observation data (w:J2000 epoch)
Right ascension19h 53m 46.11s[1]
Declination+18° 46′ 42.3″[1]
Distance12 kly[citation needed] (3.7 kpc)
Apparent magnitude (V)+6.1[1]
Apparent dimensions (V)7′.2
Physical characteristics
Masskg ( M)
Radius13 ly[2]
Estimated age9-10 Gyr
Other designationsM71, NGC 6838, GCl 115[1]

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

M71 was long thought (until the 1970s) to be a densely packed w:open cluster and was classified as such by leading w:astronomers in the field of star cluster research due to its lacking a dense central compression , its stars having more "metals" than is usual for an ancient globular cluster, and further its lacking the RR Lyrae "cluster" variable stars that are common in most globulars. However, modern photometric photometry has detected a short "w: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.

External links


  1. a b c d "SIMBAD Astronomical Database". Results for NGC 6838. Retrieved 2006-11-17.
  2. distance × sin( diameter_angle / 2 ) = 13 ly. radius