Beta Sagittarii

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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 probable binary star) and β2 Sagittarii. 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,[1] and β1 Sagittarii B (sometimes designated Arkab Prior A and B). β2 Sagittarii is named Arkab Posterior.[1] Beta Sagittarii is also referred to by the traditional name Arkab.


β Sagittarii (Latinised to Beta Sagittariii) is the groups'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).[2]

The system's traditional name Arkab derives from the Arabic عرقوب carqūb meaning Achilles Tendon.[3] The two constituents bore the traditional names Arkab Prior and Arkab Posterior since β1 leads β2 (or β2 follows β1) across the sky.[citation needed] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[4] 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.[5] 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.[1]

β1 and β2 Sagittarii, together with Alpha Sagittarii, were Al Ṣuradain (الصردين), the two Surad, "desert birds".[6]

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.)[7]


USS Arkab (AK-130) was a United States Navy Crater class cargo ship named after the system.


  1. ^ a b c "IAU Catalog of Star Names". Retrieved 13 October 2016.
  2. ^ 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:1012.0707 [astro-ph.SR].
  3. ^ - تعريف و معنى عرقوب في معجم المعاني الجامع - معجم عربي عربي تعريف و معنى عرقوب في معجم المعاني الجامع - معجم عربي عربي
  4. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  5. ^ "Bulletin of the IAU Working Group on Star Names, No. 2" (PDF). Retrieved 12 October 2016.
  6. ^ 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.
  7. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 2 日