Messier 71

53. Messier 71


Messier 71  RA: 19h 53.8'  Dec: +18 47'   Sagitta (Sge)

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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.This star cluster is about 12,000 light years away from Earth and spans 27 light-years (8 pc). The irregular variable star Z Sagittae is a member.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☉.
 

Image Information

Location Fingal ON
Date Sep 24 2011
Optics Celestron C9.25
Filters Celestron FR/FF f/6.3
Mount Celestron CGE
Camera Canon/Hutech 500DH
ISO 800
Subexposures 9
Exposure Length 180
Guider WO ZS66SD/ST-4
 

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All images copyright © 2006-2021, Rick Saunders
Main text descriptions sourced from Wikipaedia.
Sky position information is based on IP geolocation and is therefore approximate.