Open cluster in the constellation Sagittarius
Messier 18 orM18 , also designatedNGC 6613 and sometimes known as theBlack Swan Cluster , is anopen cluster ofstars in theconstellation Sagittarius . It was discovered byCharles Messier in 1764 and included in his list ofcomet -like objects.[ 8] Earth , M18 is situated between theOmega Nebula (M17) and theSmall Sagittarius Star Cloud (M24).[ 3]
This is a sparse[ 9] [ 5] tidal radius of 7.3 pc,[ 6] [ 10] Trumpler class ofII 3 p .[ 4] [ 6] M ☉ [ 5] Be star and 29B-type stars in total.[ 9] supergiant stars , all ofclass A orearlier .[ 11] HD 168352, is aB-type giant star with a class of B2 III and avisual magnitude of 8.65.[ 4]
Messier 18 is 1,296 kpc[ 2] Galactic Center .[ 5] eccentricity of 0.02. This carries it to as close as 6.5 kpc to, and as far as 6.8 kpc from the galactic core. It passes vertically through the galactic plane once every 27.4 million years, ranging no more than 80 pc above or below.[ 1]
As of January 2022, Messier 18 is one of the few remaining objects within the Messier Catalog to not have been photographed by theHubble Space Telescope .[ 12]
^a b c Wu, Zhen-Yu; et al. (November 2009), "The orbits of open clusters in the Galaxy",Monthly Notices of the Royal Astronomical Society 399 (4):2146– 2164,arXiv :0909.3737 Bibcode :2009MNRAS.399.2146W ,doi :10.1111/j.1365-2966.2009.15416.x S2CID 6066790 . ^a b Kharchenko, N. V.; et al. (2005), "Astrophysical parameters of Galactic open clusters",Astronomy and Astrophysics ,438 (3):1163– 1173,arXiv :astro-ph/0501674 Bibcode :2005A&A...438.1163K ,doi :10.1051/0004-6361:20042523 ,S2CID 9079873 . ^a b Frommert, Hartmut; Kronberg, Christine (August 21, 2007),Messier 18 , retrieved2018-11-11 . ^a b c Lindoff, U. (December 1971), "The open clusters NGC 6613 (M 18) and NGC 6716",Astronomy and Astrophysics ,15 :439– 449,Bibcode :1971A&A....15..439L . ^a b c d e Joshi, Y. C.; et al. (October 2016), "Study of open clusters within 1.8 kpc and understanding the Galactic structure",Astronomy & Astrophysics ,593 : 13,arXiv :1606.06425 Bibcode :2016A&A...593A.116J ,doi :10.1051/0004-6361/201628944 ,S2CID 118610932 , A116. ^a b c Piskunov, 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 ^ "M 18" .SIMBAD Centre de données astronomiques de Strasbourg . RetrievedNovember 11, 2018 .^ Adam, Len (2018),Imaging the Messier Objects Remotely from Your Laptop 117– 120,Bibcode :2018imor.book.....A ,ISBN 978-3319653853 ^a b McSwain, M. Virginia; Gies, Douglas R. (November 2005), "The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters",The Astrophysical Journal Supplement Series ,161 (1):118– 146,arXiv :astro-ph/0505032 Bibcode :2005ApJS..161..118M ,doi :10.1086/432757 ,S2CID 14498164 . ^ Santos-Silva, T.; Gregorio-Hetem, J. (November 6, 2012), "Characterisation of young stellar clusters",Astronomy & Astrophysics ,547 : A107,arXiv :1209.1585 Bibcode :2012A&A...547A.107S ,doi :10.1051/0004-6361/201219695 ,S2CID 119213441 . ^ Eggenberger, P.; et al. (May 2002), "The blue to red supergiant ratio in young clusters at various metallicities",Astronomy and Astrophysics ,386 (2):576– 582,arXiv :astro-ph/0202478 Bibcode :2002A&A...386..576E ,doi :10.1051/0004-6361:20020262 ,S2CID 14373322 . ^ "Explore - the Night Sky | Hubble's Messier Catalog" . 28 August 2017.^ "Stellar Lab in Sagittarius" ,www.eso.org , retrieved11 August 2016 .
6001 to 6100 6101 to 6200 6201 to 6300 6301 to 6400 6401 to 6500 6501 to 6600 6601 to 6700 6701 to 6800 6801 to 6900 6901 to 7000
