Messier 71
| Messier 71 | |
|---|---|
 M71 from Hubble Space Telescope; 3.35′ view Credit: NASA/STScI/WikiSky |
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| Observation data (J2000 epoch) | |
| Class | X-XI |
| Constellation | Sagitta |
| Right ascension | 19h 53m 46.11s[1] |
| Declination | +18° 46′ 42.3″[1] |
| Distance | 12 kly[citation needed] (3.7 kpc) |
| Apparent magnitude (V) | +6.1[1] |
| Apparent dimensions (V) | 7′.2 |
| Physical characteristics | |
| Radius | 13 ly[2] |
| Estimated age | 9-10 Gyr |
| Other designations | M71, NGC 6838, GCl 115[1] |
| See also: Globular cluster, List of globular clusters | |
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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 its stars having more "metals" than is usual for an ancient globular cluster; furthermore, it's lacking 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.
[edit] References
- ^ a b c d "SIMBAD Astronomical Database". Results for NGC 6838. http://simbad.u-strasbg.fr/Simbad. Retrieved 2006-11-17.
- ^ distance × sin( diameter_angle / 2 ) = 13 ly. radius
[edit] External links
- Messier71 @ SEDS Messier pages
- Messier 71, Galactic Globular Clusters Database page
- Messier 71, LRGB CCD image based on two hours total exposure
- Messier 71 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
- Messier 71: an Unusual Globular Cluster, ESA\Hubble picture of the week.
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Coordinates: 
19h 53m 46.11s, +18° 46′ 42.3″
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