|Observation data (J2000 epoch)|
|Right ascension||19h 16m 42s|
|Declination||−16° 17′ 00″|
|Distance||1,000 ly (300 pc)|
|Apparent dimensions (V)||> 60′|
|Radius||> 9 ly|
|Other designations||NGC 6774|
Ruprecht 147 or NGC 6774 is a dispersed star cluster in the Milky Way galaxy. It is about 1,000 light years away, which is close to Earth in comparison with other such clusters. In late summer, it can be seen with binoculars in the constellation of Sagittarius. The stars, bound by gravity, are about 2.5 to 3.25 billion years old. The cluster, discovered in 1830 by John Herschel, was sometimes thought to be an asterism (a random collection of stars) due to its sparseness and location against the background of the richest part of the Milky Way, and also since the brightest stars in this old cluster perished long ago. In 1966 the Czech astronomer Jaroslav Ruprecht classified it as a type III 2 m open cluster under the Trumpler scheme. It received otherwise little attention until 2012, when it was identified as a potentially important reference gauge for stellar and Galactic astrophysics research, particularly the research of Sun-like stars.
- "NGC 6774". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 May 2016.
- Curtis, Jason L.; Wolfgang, Angie; Wright, Jason T.; Brewer, John M.; Johnson, John Asher (2013). "Ruprecht 147: The Oldest Nearby Open Cluster as a New Benchmark for Stellar Astrophysics". The Astronomical Journal. 145 (5): 134. arXiv:1206.6533. Bibcode:2013AJ....145..134C. doi:10.1088/0004-6256/145/5/134. ISSN 1538-3881.
- Ruprecht, J. (1966). "Classification of open star clusters". Bulletin of the Astronomical Institutes of Czechoslovakia. 17: 33. Bibcode:1966BAICz..17...33R. ISSN 0004-6248.
- "Nearby star cluster, long forgotten, now discovered to be useful in studies of Sun and search for planets like Earth". Phys.org. 23 June 2012.
- Wright, Jason. "Ruprecht 147: The Oldest Nearby Galactic Cluster". AstroWright. PSU. Retrieved 20 May 2016.
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