Beta Sagittarii

Beta¹ Sagittarii

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

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

Beta² Sagittarii

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

• 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.)
• These two Betas star, together with α Sgr too, were Al Ṣuradain (ألسردين), the two Surad, desert birds.

Namesakes

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