Magnitude 3.96 Apparent magnitude (V) 3.96 | Constellation Sagittarius | |
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Similar Delta Sagittarii, Gamma2 Sagittarii, Lambda Sagittarii, Epsilon Sagittarii, Zeta Sagittarii | ||
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.
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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.
Nomenclature
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.
β¹ and β² Sagittarii, together with Alpha Sagittarii, were Al Ṣuradain (السردين), the two Surad, "desert birds".
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.)
Namesakes
USS Arkab (AK-130) was a United States Navy Crater class cargo ship named after the system.
Properties
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.
β² Sagittarii is a spectral type F2 giant which has an apparent magnitude of +4.27.