Lambda Sagittarii

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λ Sagittarii
Sagittarius constellation map.svg
Red circle.svg
Location of λ Sagittarii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagittarius
Right ascension  18h 27m 58.24072s[1]
Declination −25° 25′ 18.1146″[1]
Apparent magnitude (V) +2.82[2]
Spectral type K0 IV[3]
U−B color index +0.903[4]
B−V color index +1.045[4]
Radial velocity (Rv)−43.5[2] km/s
Proper motion (μ) RA: −44.76[1] mas/yr
Dec.: −185.66[1] mas/yr
Parallax (π)41.72 ± 0.16[1] mas
Distance78.2 ± 0.3 ly
(23.97 ± 0.09 pc)
Absolute magnitude (MV)1.07±0.008[5]
Mass2.6[6] M
Radius11[7] R
Surface gravity (log g)2.90[8] cgs
Temperature4,770[8] K
Metallicity [Fe/H]–0.20[9] dex
Rotational velocity (v sin i)3.81[8] km/s
Other designations
Kaus Borealis, λ Sagittarii, 22 Sagittarii, CPD-25  6523, FK5 692, GC 25180, HD 169916, HIP 90496, HR 6913, PPM 268438, SAO 186841.
Database references

Lambda Sagittarii (λ Sagittarii, abbreviated Lambda Sgr, λ Sgr), formally named Kaus Borealis /ˈkɔːs bɒriˈælɪs/,[10][11] is a star in the southern constellation of Sagittarius. The star marks the top of the Archer's bow.


With an apparent visual magnitude of +2.82,[2] this is one of the brighter members of the constellation and, according to the Bortle Dark-Sky Scale, it is readily visible to the naked eye. Based upon parallax measurements, it is 78.2 light-years (24.0 parsecs) from the Sun.[1]

Being 2.1 degrees south of the ecliptic, Lambda Sgr is sometimes occulted by the Moon and, rarely, by a planet. The last planet to pass in front of it was Venus, on 19 November 1984. The previous occasion was 5 December 1865, when it was occulted by Mercury.[citation needed]

Kaus Borealis is a subgiant star with a stellar classification of K0 IV.[3] It has a mass 2.6 times that of the Sun.[6] The interferometry-measured angular diameter of this star, after correction for limb darkening, is 4.24 ± 0.05 mas.[12] At the estimated distance of Lambda Sagittarii,[1] this yields a physical size of about 11 times the radius of the Sun.[7] This expanded outer envelope is radiating energy at an effective temperature of 4,770 K,[8] causing it to glow with the cool orange hue of a K-type star.[13] It appears to be rotating at a leisurely rate, with a projected rotational velocity of 3.81 km s−1.[8]


λ Sagittarii (Latinised to Lambda Sagittarii) is the star's Bayer designation.

It bore the traditional name Kaus Borealis, which derives from the Arabic قوس qaws 'bow' and Latin boreālis 'northern'. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[15] included a table of the first two batches of names approved by the WGSN; which included Kaus Borealis for this star.

This star, with Gamma Sagittarii, Delta Sagittarii, Epsilon Sagittarii, Zeta Sagittarii, Sigma Sagittarii, Tau Sagittarii and Phi Sagittarii comprises the Teapot asterism.[16]

In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Rai al Naaim, which was translated into Latin as Pastor Struthionum, meaning keeper of the ostriches.[17]

This star is Al Tizini's Rāʽi al Naʽāïm (ألراع ٱلنعم), the Keeper of the Naʽams (Ostrich), meaning the "keeper" the two asterisms Al Naʽām al Wārid (النعم الوارد), "The Going Ostriches" and Al Naʽām al Ṣādirah (النعم السادرة), "The Returning Ostriches".[18]

In Chinese, (Dǒu), meaning Dipper, refers to an asterism consisting of Lambda Sagittarii, Phi Sagittarii, Mu Sagittarii, Sigma Sagittarii, Tau Sagittarii and Zeta Sagittarii. Consequently, Lambda Sagittarii itself is 斗宿二 (Dǒu Sù èr, English: the Second Star of Dipper.)[19]


  1. ^ a b c d e f g van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. ^ a b c Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, Astronomisches Rechen-Institut Heidelberg, 35 (35): 1, Bibcode:1999VeARI..35....1W.
  3. ^ a b Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637.
  4. ^ a b Gutierrez-Moreno, Adelina; et al. (1966), "A System of photometric standards", Publ. Dept. Astron. Univ. Chile, Publicaciones Universidad de Chile, Department de Astronomy, 1: 1–17, Bibcode:1966PDAUC...1....1G.
  5. ^ Park, Sunkyung; et al. (2013), "Wilson-Bappu Effect: Extended to Surface Gravity", The Astronomical Journal, 146 (4): 73, arXiv:1307.0592, Bibcode:2013AJ....146...73P, doi:10.1088/0004-6256/146/4/73.
  6. ^ a b Edvardsson, B. (January 1988), "Spectroscopic surface gravities and chemical compositions for 8 nearby single sub-giants", Astronomy and Astrophysics, 190 (1–2): 148–166, Bibcode:1988A&A...190..148E.
  7. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3 ed.), Birkhäuser, ISBN 3540296921. The radius (R*) is given by:
  8. ^ a b c d e Hekker, S.; Meléndez, J. (2007), "Precise radial velocities of giant stars. III. Spectroscopic stellar parameters", Astronomy and Astrophysics, 475 (3): 1003–1009, arXiv:0709.1145, Bibcode:2007A&A...475.1003H, doi:10.1051/0004-6361:20078233.
  9. ^ McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances", Astrophysical Journal Supplement Series, 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527.
  10. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  11. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  12. ^ Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.
  13. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 10, 2012, retrieved 2012-01-16.
  14. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  15. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  16. ^ "Teapot". Retrieved 2017-05-13.
  17. ^ Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society. 55: 430. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
  18. ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 355. ISBN 0-486-21079-0. Retrieved 2012-09-04.
  19. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日

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