Eta Boötis

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η Boötis
Boötes constellation map.svg
Red circle.svg

Location of η Boötis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Boötes
Right ascension 13h 54m 41.07892s[1]
Declination +18° 23′ 51.7946″[1]
Apparent magnitude (V) 2.680[2]
Spectral type G0 IV[3]
U−B color index +0.207[4]
B−V color index +0.585[4]
R−I color index 0.2
Radial velocity (Rv) -1.6[2] km/s
Proper motion (μ) RA: -60.95[1] mas/yr
Dec.: -356.29[1] mas/yr
Parallax (π) 87.75 ± 1.24[1] mas
Distance 37.2 ± 0.5 ly
(11.4 ± 0.2 pc)
Absolute magnitude (MV) 2.41[2]
Mass 1.71 ± 0.05[5] M
Radius 2.672 ± 0.028[5] R
Luminosity 8.89 ± 0.16[5] L
Surface gravity (log g) 3.817 ± 0.015[5] cgs
Temperature 6,100 ± 28[5] K
Metallicity [Fe/H] +0.27[2] dex
Rotational velocity (v sin i) 11.8[6] km/s
Age 2.7[3] Gyr
Other designations
Muphrid, Mufride, Muphride, Mufrid, Saak, 8 Boötis, Gl 534, HR 5235, BD +19°2725, HD 121370, LTT 14060, GCTP 3175.00, SAO 100766, FK5 513, HIP 67927
Database references

Eta Boötis (η Boötis, abbreviated Eta Boo, η Boo), also named Muphrid,[7] is a star in the constellation of Boötes. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[8]


η Boötis (Latinised to Eta Boötis) is the star's Bayer designation. It also bears the Flamsteed designation of 8 Boötis.

It bore the traditional names Muphrid and Saak.[9] Muphrid is from the Arabic مفرد الرامح mufrid ar-rāmiħ "the (single) one of the lancer".[10] In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Ramih al Ramih (رمح الرامح rumḥ al rāmiḥ), which was translated into Latin as Lancea Lanceator, possibly meaning the lance of the lancer.[11] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[12] to catalogue and standardize proper names for stars. The WGSN approved the name Muphrid for this star on 12 September 2016 and it is now so entered in the IAU Catalog of Star Names.[7]

In Chinese, 右攝提 (Yòu Niè Dī), meaning "the Right Conductor", refers to an asterism consisting of Eta Boötis, Tau Boötis and Upsilon Boötis.[13] Consequently, Eta Boötis itself is known as 右攝提一 (Yòu Niè Dī yī, English: "the First Star of the Right Conductor").[14]


Eta Boötis is a subgiant that has begun the process of evolving from a main sequence star into a red giant. It has about 1.7 times the mass of the Sun and 2.7 times the Sun's radius. The estimated age of this star is about 2.7 billion years.[3] Based on its spectra, it has a significant excess of elements heavier than helium.[2] In fact the ratio of iron to hydrogen is considered close to the upper limit for dwarf stars in the galactic disk.[15] The star is a suspected spectroscopic binary with a reported period of 494 days, but the companion was not confirmed through speckle interferometry. This measurement does not rule out a low mass stellar companion of spectral class M7.[5]

Eta Boötis appears close to the prominent star Arcturus (Alpha Bootis) in Earth's sky, and Arcturus is in fact its closest stellar neighbor, as both stars are nearly identical in distance from the Sun. The two stars are about 3.24 light years apart,[16] and each would appear bright in the other's sky. Arcturus would appear as roughly magnitude -5.2 (about 120 times brighter than it appears from Earth, or close to twice the brightness of Venus) in the night sky of a hypothetical planet orbiting Eta Boötis, while Eta Boötis would appear at about magnitude −2.4 (absolute magnitude −2.41 at 0.99 parsec) in the sky of a hypothetical planet orbiting Arcturus, or over twice the brightness of Sirius in the night sky.

See also[edit]


  1. ^ a b c d e van Leeuwen, Floor (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752v1Freely accessible, doi:10.1051/0004-6361:20078357  Note: see VizieR catalogue I/311.
  2. ^ a b c d e Holmberg, J.; Nordström, B.; Andersen, J. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, Bibcode:2009A&A...501..941H, arXiv:0811.3982Freely accessible, doi:10.1051/0004-6361/200811191 
  3. ^ a b c Thévenin, F.; et al. (June 2005), "VLTI/VINCI diameter constraints on the evolutionary status of δ Eri, ξ Hya, η Boo", Astronomy and Astrophysics, 436 (1): 253–262, Bibcode:2005A&A...436..253T, arXiv:astro-ph/0501420Freely accessible, doi:10.1051/0004-6361:20042075 
  4. ^ a b Oja, T., "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series, 65 (2): 405–4 
  5. ^ a b c d e f van Belle, Gerard T.; Ciardi, David R.; Boden, Andrew F. (March 2007), "Measurement of the Surface Gravity of η Bootis", The Astrophysical Journal, 657 (2): 1058–1063, Bibcode:2007ApJ...657.1058V, arXiv:astro-ph/0701120Freely accessible, doi:10.1086/510830 
  6. ^ Schröder, C.; Reiners, A.; Schmitt, J. H. M. M. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo", Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377 
  7. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  8. ^ 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, retrieved 2012-02-04 
  9. ^ Rumrill, H. B. (June 1936), "Star Name Pronunciation", Publications of the Astronomical Society of the Pacific, 48 (283): 139–154, 150, Bibcode:1936PASP...48..139R, doi:10.1086/124681 
  10. ^ Cannon, Garland Hampton (1994), The Arabic contributions to the English language: an historical dictionary, Otto Harrassowitz Verlag, p. 264, ISBN 3-447-03491-2 
  11. ^ 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 (8): 429, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429 
  12. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016. 
  13. ^ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  14. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived January 30, 2011, at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.
  15. ^ Bensby, T.; Zenn, A. R.; Oey, M. S.; Feltzing, S. (2007). "Tracing the Galactic Thick Disk to Solar Metallicities". The Astrophysical Journal. 663: L13. Bibcode:2007ApJ...663L..13B. arXiv:0705.2060Freely accessible. doi:10.1086/519792. 
  16. ^

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