Beta Sagittarii

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Beta¹ Sagittarii
Diagram showing star positions and boundaries of the Sagittarius constellation and its surroundings
Cercle rouge 100%.svg

Location of β¹ Sagittarii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagittarius
Right ascension 19h 22m 38.3s
Declination −44° 27' 32"
Apparent magnitude (V) +3.96
Distance 378 ± 42 ly
(116 ± 13 pc)
Spectral type B9V
Other designations
Arkab Prior, β¹ Sagittarii, β¹ Sgr, Beta¹ Sgr, CCDM J19226-4428A, CPD-40  8955, FK5 1502, GC 26703, HD 181454, HIP 95241, HR 7337, PPM 325041 , SAO 229646, WDS J19226-4428A

The Bayer designation Beta Sagittarii (Beta Sgr, β Sagittarii, β Sgr) is shared by two star systems, β¹ Sagittarii and β² Sagittarii, in the constellation Sagittarius. The two stars are separated by 0.36° in the sky. Beta Sagittarii also has the traditional name Arkab.

β¹ Sagittarii[edit]

Beta¹ Sagittarii (Beta¹ Sgr, β¹ Sagittarii, β¹ Sgr), also called Arkab Prior since it leads β² across the sky, is a binary star lying 378 light years from Earth. Arkab Prior A is a spectral type B9 main sequence dwarf which has an apparent magnitude of +3.96. Arkab Prior 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[edit]

Beta² Sagittarii
Diagram showing star positions and boundaries of the Sagittarius constellation and its surroundings
Cercle rouge 100%.svg

Location of β² Sagittarii (circled)
Observation data
Epoch       Equinox
Constellation Sagittarius
Right ascension 19h 23m 13.2s
Declination -44° 47' 59"
Apparent magnitude (V) +4.27
Distance 139 ± 5 ly
(43 ± 2 pc)
Spectral type F2III
Other designations
Arkab Posterior, β² Sagittarii, β² Sgr, Beta² Sgr, CPD-45  9701, GC 26718, HD 181623, HIP 95294, HR 7343, PPM 325051, SAO 229654,

Beta² Sagittarii (Beta² Sgr, β² Sagittarii, β² Sgr), also called Arkab Posterior since it trails β¹ across the sky, is a spectral type F2 giant which has an apparent magnitude of +4.27. It is 137 light years from Earth.

Name and etymology[edit]

  • The name Arkab is from the Arabic عرقوب carqūb meaning hamstring
  • *In Chinese, 天淵 (Tiān Yuān), meaning Celestial Spring, refers to an asterism consisting of β¹ Sagittarii, β² Sagittarii, and α Sagittarii, . Consequently, β¹ Sagittarii 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.)[1]
  • These two Betas star, together with α Sgr too, were Al Ṣuradain (ألسردين), the two Surad, desert birds.[2]

Namesakes[edit]

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

References[edit]

  1. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 2 日
  2. ^ 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.