Messier 7 orM7, also designatedNGC 6475 and sometimes known as thePtolemy Cluster,[4] is anopen cluster ofstars in theconstellation ofScorpius. The cluster is easily detectable with thenaked eye, close to the "stinger" of Scorpius. With adeclination of −34.8°, it is the southernmostMessier object.
| Messier 7 | |
|---|---|
 | |
| Observation data (J2000.0epoch) | |
| Right ascension | 17h 53m 51.2s[1] |
| Declination | −34° 47′ 34″[1] |
| Distance | 980 ± 33 ly (300 ± 10 pc)[2] |
| Apparent magnitude (V) | 3.3 |
| Apparent dimensions (V) | 80.0′ |
| Physical characteristics | |
| Mass | 735[3] M☉ |
| Radius | 25 ly |
| Estimated age | 200 Myr[2] |
| Other designations | Ptolemy Cluster,M7,NGC 6475,Cr 354 |
| Associations | |
| Constellation | Scorpius |
| See also:Open cluster,List of open clusters | |
M7 has been known sinceantiquity; it was first recorded by the 2nd-century Greek-Roman astronomerPtolemy, who described it as anebula in 130 AD.[5] Italian astronomerGiovanni Batista Hodierna observed it before 1654 and counted 30stars in it. In 1764, French astronomerCharles Messier catalogued the cluster as the seventh member in his list ofcomet-like objects. English astronomerJohn Herschel described it as "coarsely scattered clusters of stars".[4]
Telescopic observations of the cluster reveal about 80 stars within a field of view of 1.3° across. At the cluster's estimated distance of 980light years this corresponds to an actual diameter of 25 light years. Thetidal radius of the cluster is 40.1 ly (12.3 pc) and it has a combined mass of about 735 times the mass of theSun.[3] The age of the cluster is around 200[2] million years while the brightest member star is ofmagnitude 5.6. In terms of composition, the cluster contains a similar abundance of elements other than hydrogen and helium as the Sun.[2]
On August 29, 2006, Messier 7 was used forfirst light image of theLong Range Reconnaissance Imager (LORRI) telescope on the Pluto-boundNew Horizons spacecraft.[6]
As of January 2022, Messier 7 is one of the few remainingMessier objects not photographed by theHubble Space Telescope.[7] This is mainly due to those objects'angular diameter or lack of scientific significance. Most such objects are open clusters of large angular diameter that would require thousands of photos due to Hubble's small field of view. (For comparison, Hubble's well known panoramic photo of theAndromeda Galaxy, covering less than half of our galactic neighbor, required approximately 400 individual movements and 7400 exposures.)[8]
Gallery
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M7 on the night sky. It is easily visible to the naked eye and located between the constellations Scorpius and Sagittarius.
Broader view of M7, with the cluster at the center of the image
See also
editReferences
edit- ^ab"MESSIER 007",NASA/IPAC Extragalactic Database, NASA, retrieved2012-04-19
- ^abcdVillanova, S.; Carraro, G.; Saviane, I. (September 2009), "A spectroscopic study of the open cluster NGC 6475 (M 7). Chemical abundances from stars in the range Teff = 4500-10 000 K",Astronomy and Astrophysics,504 (3):845–852,arXiv:0906.4330,Bibcode:2009A&A...504..845V,doi:10.1051/0004-6361/200811507,S2CID 17534818
- ^abPiskunov, A. E.; et al. (January 2008), "Tidal radii and masses of open clusters",Astronomy and Astrophysics,477 (1):165–172,Bibcode:2008A&A...477..165P,doi:10.1051/0004-6361:20078525
- ^abGendler, Robert; Christensen, Lars Lindberg; Malin, David (2011),Treasures of the Southern Sky: A Photographic Anthology, Springer, p. 139,ISBN 978-1461406273
- ^Jones, Kenneth Glyn (1991),Messier's Nebulae and Star Clusters, The Practical astronomy handbook series (2ns ed.),Cambridge University Press, p. 1,ISBN 978-0521370790
- ^"LORRI's First Light1". pluto.jhuapl.edu. Retrieved2018-10-24.
- ^"Explore - the Night Sky | Hubble's Messier Catalog". 28 August 2017.
- ^"Hubble's High-Definition Panoramic View of the Andromeda Galaxy". 24 March 2015.
External links
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- Messier 7, SEDS Messier pages
- Messier 7 onWikiSky:DSS2,SDSS,GALEX,IRAS,Hydrogen α,X-Ray,Astrophoto,Sky Map,Articles and images
- NASA Astronomy Picture of the Day: M7: Open Star Cluster in Scorpius (12 September 2012)
- New Horizons probe captures M7
- NASA Astronomy Picture of the Day: M7: Open Star Cluster in Scorpius (13 July 2016)
