Alkaid

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Template:Short description

Alkaid
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) +1.86[2]
Characteristics
Evolutionary stage main sequence[3]
Spectral type B3 V[4]
U−B color index −0.68[2]
B−V color index −0.19[2]
Astrometry
Radial velocity (Rv)−10.9[5] km/s
Proper motion (μ) RA: −121.17[1] mas/yr
Dec.: −14.91[1] mas/yr
Parallax (π)31.38±0.24 mas[1]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)−0.67[6]
Details[3]
Mass5.071±0.023 M☉
Radius2.894 (equatorial)
2.665 (polar) R☉
Luminosity574 L☉
Surface gravity (log g)3.78[7] cgs
Temperature16,329 (equatorial)
17,720 (polar) K
Rotation14.6 (equatorial) days
15.6 (polar) days
Rotational velocity (v sin i)154.3±9.1 km/s
Age6+2
−4 Myr
Other designations
Alkaid, Benetnash, Benetnasch,[8] Elkeid, η UMa, 85 UMa, BD+50°2027, FK5 509, GC 18643, HD 120315, HIP 67301, HR 5191, PPM 53742, SAO 44752.
Database references
SIMBADdata

Alkaid /ælˈkeɪd/, also called Eta Ursae Majoris (Latinised from η Ursae Majoris, abbreviated Eta UMa, η UMa),[9][10] is a star in the constellation of Ursa Major. It is the easternmost star in the Big Dipper (or Plough) asterism. However, unlike most stars of the Big Dipper, it is not a member of the Ursa Major moving group.[11] With an apparent visual magnitude of +1.86, it is the third-brightest star in the constellation and one of the brightest stars in the night sky.

Physical properties

File:Alkaid and Sun from 0,23 UA.jpg
Comparison of Alkaid (left) and the Sun (right)

Alkaid is a B-type main sequence star with a stellar classification of B3 V.[4] Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[12]

Allaid has 5.07 times the mass of the Sun. It is a young star, roughly six million years old, and is in the beginning of its life in the main sequence (ZAMS). The star rotates rapidly, with a projected rotational velocity of 154.3±9.1 km/s. Correcting for its inclination angle of 42° implies an equatorial rotational velocity of 240 km/s. As a consequence of its rapid rotation, Alkaid is oblate, with a radius of 2.89 solar radii (R☉) at the equator, and 2.66 solar radii at the poles. The effective temperature also vary across latitudes, being of 16,300 K at the equator and 17,700 K at the poles.[3] Such a temperature gives it the blue-white hue of a B-type star.[13] This star is an X-ray emitter with a luminosity of 9.3 × 1028 erg s−1.[14]

Eta Ursae Majoris was listed as a standard star for the spectral type B3 V. It has broadened absorption lines due to its rapid rotation, which is common in stars of this type. However, the lines are very slightly distorted and variable, which may be caused by some emission from a weak disk of material produced by the rapid rotation.[15]

Alkaid is a relatively nearby and bright star and has been examined closely, but no exoplanets or companion stars have been discovered.[16][17]

Nomenclature

η Ursae Majoris (Latinised to Eta Ursae Majoris) is the star's Bayer designation. The International Astronomical Union has formally chosen the proper name Alkaid for this star.[18]

It bore the traditional names Alkaid (or Elkeid from the Arabic القايد القائد) and Benetnasch /ˈbɛnɛtnæʃ/.[9] Alkaid derives from the Arabic phrase meaning "The leader of the daughters of the bier" (Script error: No such module "Lang". Script error: No such module "lang".). The daughters of the bier, i.e. the mourning maidens, are the three stars of the handle of the Big Dipper, Alkaid, Mizar, and Alioth; while the four stars of the bowl, Megrez, Phecda, Merak, and Dubhe, are the bier.

It is known as Běidǒuqī (北斗七 - the Seventh Star of the Northern Dipper) or Yáoguāng (瑤光 - the Star of Twinkling Brilliance) in Chinese.[19]

The Hindus viewed this star as Marīci (Template:Langx), one of the seven Saptarshis (Template:Langx).[20]

In Japan and Korea, Alkaid is known as Hagunsei and Mukokseong respectively ("the military breaking star" or "most corner star"). Both meanings come from ancient China's influence in both countries.[citation needed]

In culture

USS Alkaid (AK-114) was a United States Navy Crater class cargo ship named after the star.[21]

Alkaid is one of the Behenian fixed stars, used in Alchemy.[citation needed]

The fossil starfish Alkaidia is named after Alkaid.[22]

References

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  1. ^ a b c d e Page Module:Citation/CS1/styles.css has no content.van Leeuwen, Floor (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752v1. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600. Note: see VizieR catalogue I/311.
  2. ^ a b c Page Module:Citation/CS1/styles.css has no content.Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
  3. ^ a b c Page Module:Citation/CS1/styles.css has no content.Lazzarotto, Axel; Hui-Bon-Hoa, Alain; Böhm, Torsten; Gent, Matt; Rieutord, Michel (2026-04-24). "Fundamental properties of two rapidly rotating stars: Rasalhague and Alkaid". Astronomy & Astrophysics. arXiv:2604.11189. doi:10.1051/0004-6361/202659029. ISSN 0004-6361.
  4. ^ a b Page Module:Citation/CS1/styles.css has no content.Morgan, W. W.; Keenan, P. C. (1973). "Spectral Classification". Annual Review of Astronomy and Astrophysics. 11: 29. Bibcode:1973ARA&A..11...29M. doi:10.1146/annurev.aa.11.090173.000333.
  5. ^ Page Module:Citation/CS1/styles.css has no content.Wielen, R.; et al. (1999). "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions". Veröff. Astron. Rechen-Inst. Heidelb. 35 (35): 1. Bibcode:1999VeARI..35....1W.
  6. ^ Page Module:Citation/CS1/styles.css has no content.Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  7. ^ Page Module:Citation/CS1/styles.css has no content.Baines, E.; Schmitt, H. R.; Zavala, R. T.; Hutter, D.; van Belle, G. T. (2017). "Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer". The Astronomical Journal. 155 (1): 30. arXiv:1712.08109. Bibcode:2018AJ....155...30B. doi:10.3847/1538-3881/aa9d8b. S2CID 119427037.
  8. ^ Page Module:Citation/CS1/styles.css has no content.Rumrill, H. B. (1936). "Star Name Pronunciation". Publications of the Astronomical Society of the Pacific. 48 (283): 139. Bibcode:1936PASP...48..139R. doi:10.1086/124681. S2CID 120743052.
  9. ^ a b Page Module:Citation/CS1/styles.css has no content.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.
  10. ^ Page Module:Citation/CS1/styles.css has no content."IAU Catalog of Star Names". Retrieved 28 July 2016.
  11. ^ Page Module:Citation/CS1/styles.css has no content.Motz, Lloyd; Nathanson, Carol (1988). The Constellations: An Enthusiast's Guide To The Night Sky. Doubleday. p. 39. ISBN 978-0-385-17600-2.
  12. ^ Page Module:Citation/CS1/styles.css has no content.Garrison, R. F. (December 1993). "Anchor Points for the MK System of Spectral Classification". Bulletin of the American Astronomical Society. 25: 1319. Bibcode:1993AAS...183.1710G. Archived from the original on 2019-06-25. Retrieved 2012-02-04.
  13. ^ Page Module:Citation/CS1/styles.css has no content."The Colour of Stars". Australia Telescope, Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. December 21, 2004. Archived from the original on 2012-03-18. Retrieved 2012-01-16.
  14. ^ Page Module:Citation/CS1/styles.css has no content.Cassinelli, J. P.; et al. (February 1994). "X-ray emission from near-main-sequence B stars". Astrophysical Journal, Part 1. 421 (2): 705–717. Bibcode:1994ApJ...421..705C. doi:10.1086/173683.
  15. ^ Page Module:Citation/CS1/styles.css has no content.Bopp, B. W; Caplinger, J. R; Crosby, N. A; Mahoney, D. F; O'Brien, S. P; Dempsey, R. C (1989). "Is the MK Standard eta UMa an Incipient be Star?". Information Bulletin on Variable Stars. 3347: 1. Bibcode:1989IBVS.3347....1B.
  16. ^ Page Module:Citation/CS1/styles.css has no content.Howard, Andrew W; Fulton, Benjamin J (2016). "Limits on Planetary Companions from Doppler Surveys of Nearby Stars". Publications of the Astronomical Society of the Pacific. 128 (969) 114401. arXiv:1606.03134. Bibcode:2016PASP..128k4401H. doi:10.1088/1538-3873/128/969/114401. S2CID 118503912.
  17. ^ Page Module:Citation/CS1/styles.css has no content.Roberts, Lewis C; Turner, Nils H; Ten Brummelaar, Theo A (2007). "Adaptive Optics Photometry and Astrometry of Binary Stars. II. A Multiplicity Survey of B Stars". The Astronomical Journal. 133 (2): 545. Bibcode:2007AJ....133..545R. CiteSeerX 10.1.1.549.4623. doi:10.1086/510335.
  18. ^ Page Module:Citation/CS1/styles.css has no content."Naming Stars". International Astronomical Union. Archived from the original on 10 March 2025. Retrieved 18 July 2023.
  19. ^ Page Module:Citation/CS1/styles.css has no content.Ridpath, Ian. "Star Tales - Ursa Major 2". Retrieved 29 June 2025.
  20. ^ Page Module:Citation/CS1/styles.css has no content.Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 438. ISBN 978-0-486-21079-7. Retrieved 2012-09-04. {{cite book}}: ISBN / Date incompatibility (help)
  21. ^ Page Module:Citation/CS1/styles.css has no content."Alkaid (AK-114)". Naval History and Heritage Command. 11 December 2016. Retrieved 31 December 2019.
  22. ^ Page Module:Citation/CS1/styles.css has no content.Blake, Daniel B.; Reid, Robert (1998). "Some Albian (Cretaceous) asteroids (Echinodermata) from Texas and their paleobiological implications". Journal of Paleontology. 72 (3): 512–532. Bibcode:1998JPal...72..512B. doi:10.1017/S002233600002429X. ISSN 0022-3360.
  • Alkaid at Jim Kaler's Stars website

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