Epoch J2000.0 Equinox J2000.0
|Right ascension||19h 22m 38.3s|
|Declination||−44° 27' 32"|
|Apparent magnitude (V)||+3.96|
|Distance||378 ± 42 ly
(116 ± 13 pc)
|Right ascension||19h 23m 13.2s|
|Declination||-44° 47' 59"|
|Apparent magnitude (V)||+4.27|
|Distance||139 ± 5 ly
(43 ± 2 pc)
Beta Sagittarii (β Sagittarii, abbreviated Beta Sgr, β Sgr) is the common designation shared by two star systems in the constellation of Sagittarius, themselves designated β¹ Sagittarii (itself a binary star) and β² Sagittarii. β¹ and β² Sagittarii are approximately 378 and 139 light years, respectively, from Earth. The two systems are separated by 0.36° in the sky.
β¹ Sagittarii's two components are designated β¹ Sagittarii A, also named Arkab Prior, and β¹ Sagittarii B (sometimes designated Arkab Prior A and B). β² Sagittarii is named Arkab Posterior. Beta Sagittarii is also referred to by the traditional name Arkab.
β Sagittarii (Latinised to Beta Sagittariii) is the system's Bayer designation; β¹ and β² Sagittarii, those of its two constituents. The designations of β¹'s components - β¹ Sagittarii A and B - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).
The system's traditional name Arkab derives from the Arabic عرقوب carqūb meaning Achilles Tendon. The two constituents bore the traditional names Arkab Prior and Arkab Posterior since β¹ leads β² (or β² follows β¹) across the sky. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN states that in the case of multiple stars the name should be understood to be attributed to the brightest component by visual brightness. The WGSN approved the names Arkab Prior and Arkab Posterior for β¹ Sagittarii A and β² Sagittarii on 5 October 2016 and they are now so entered in the IAU Catalog of Star Names.
In Chinese, 天淵 (Tiān Yuān), meaning Celestial Spring, refers to an asterism consisting of β¹ Sagittarii, β² Sagittarii, and Alpha Sagittarii, Consequently, β¹ and β² Sagittarii themselves are known as 天淵一 (Tiān Yuān yī, English: the First Star of Celestial Spring.) and 天淵二 (Tiān Yuān èr, English: the Second Star of Celestial Spring.)
β¹ Sagittarii A is a spectral type B9 main sequence dwarf which has an apparent magnitude of +3.96. β¹ Sagittarii B is a type A3 dwarf with an apparent magnitude of +7.4. The two stars are separated in the sky by 28 arcseconds, which puts them at least 3300 astronomical units apart.
- "IAU Catalog of Star Names". Retrieved 13 October 2016.
- Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv: [astro-ph.SR].
- http://www.almaany.com/ar/dict/ar-ar/%D8%B9%D8%B1%D9%82%D9%88%D8%A8/ - تعريف و معنى عرقوب في معجم المعاني الجامع - معجم عربي عربي تعريف و معنى عرقوب في معجم المعاني الجامع - معجم عربي عربي
- IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
- "Bulletin of the IAU Working Group on Star Names, No. 2" (PDF). Retrieved 12 October 2016.
- Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 357. ISBN 0-486-21079-0. Retrieved 4 September 2012.
- (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 2 日