Eta Ophiuchi

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Eta Ophiuchi
Ophiuchus constellation map.svg
Red circle.svg

Location of η Ophiuchi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ophiuchus
Right ascension 17h 10m 22.68689s[1]
Declination –15° 43′ 29.6639″[1]
Apparent magnitude (V) 2.43[2] (3.05/3.27)[3]
Spectral type A1 IV + A1 IV[3]
U−B color index +0.09[2]
B−V color index +0.05[2]
Radial velocity (Rv) –0.9[4] km/s
Proper motion (μ) RA: +40.13[1] mas/yr
Dec.: +99.17[1] mas/yr
Parallax (π) 36.91 ± 0.80[1] mas
Distance 88 ± 2 ly
(27.1 ± 0.6 pc)
Period (P) 87.58 ± 1.00 yr
Semi-major axis (a) 1.396 ± 0.010"
Eccentricity (e) 0.950 ± 0.020
Inclination (i) 95.2 ± 2.0°
Longitude of the node (Ω) 38.9 ± 1.0°
Periastron epoch (T) 2024.68 ± 0.50
Argument of periastron (ω)
274.8 ± 2.0°
Metallicity [Fe/H] −0.01[5] dex
η Oph A
Mass 2.966[3] M
Radius 2.5/2.0[citation needed] R
Luminosity 35/21[citation needed] L
Temperature 8900/8600[citation needed] K
Rotational velocity (v sin i) 23[6] km/s
η Oph B
Mass 3.478[3] M
Other designations
35 Oph, BD–15°4467, GCTP 3895.00, Gl 656.1A/B, HD 155125, HIP 84012, HR 6378, SAO 160332, WDS J17104-1544AB.
Database references

Eta Ophiuchi, also known as η Oph or η Ophiuchi, is a star in the constellation Ophiuchus. It has the traditional name Sabik.


η Oph is actually a binary star system that is difficult to resolve in amateur telescopes but whose true nature has been determined through use of more advanced techniques. The "primary" star (whose observational data make up the table in this article), which could nominally be referred to as η Oph A, is actually only slightly larger and hotter than its companion, η Oph B. Individually each star is a fairly unremarkable A class main sequence star, but as a binary pair they are unusual. Each star orbits around a common center in a close and highly elliptical orbit, making planetary formation unlikely in this system and some stellar data imprecise.[citation needed]

η Oph is the northern pole star of the planet Uranus.[citation needed]

In culture[edit]

In Chinese, this star is considered part of 天市左垣 (Tiān Shì Zuǒ Yuán), meaning Left Wall of Heavenly Market Enclosure, which refers to an asterism (pattern of stars) representing eleven old states in China that mark the left borderline of the enclosure, consisting of η Ophiuchi, δ Herculis, λ Herculis, μ Herculis, ο Herculis, 112 Herculis, ζ Aquilae, θ1 Serpentis, η Serpentis, ν Ophiuchi and ξ Serpentis.[7] Consequently, η Ophiuchi itself is known as 天市左垣十一 (Tiān Shì Zuǒ Yuán shíyī, English: the Eleventh Star of Left Wall of Heavenly Market Enclosure), representing the state Song(宋).[8][9]

USS Sabik (AK-121) was a United States Navy Crater class cargo ship named after the star.


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752free to read, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c Hoffleit, D.; Warren, Jr., W. H. (1991). "Entry for HR 2491". Bright Star Catalogue, 5th Revised Ed. (Preliminary Version). CDS.  ID V/50.
  3. ^ a b c d e Docobo, J. A.; Ling, J. F. (April 2007), "Orbits and System Masses of 14 Visual Double Stars with Early-Type Components", The Astronomical Journal, 133 (4): 1209–1216, Bibcode:2007AJ....133.1209D, doi:10.1086/511070 
  4. ^ Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Washington, Washington: Carnegie Institution of Washington: 0, Bibcode:1953GCRV..C......0W 
  5. ^ Gray, R. O.; Corbally, C. J.; Garrison, R. F.; McFadden, M. T.; Bubar, E. J.; McGahee, C. E.; O'Donoghue, A. A.; Knox, E. R. (2006). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc--The Southern Sample". The Astronomical Journal. 132: 161. arXiv:astro-ph/0603770free to read. Bibcode:2006AJ....132..161G. doi:10.1086/504637. 
  6. ^ Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785free to read, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224 
  7. ^ (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.
  8. ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
  9. ^ (Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name Archived August 10, 2010, at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.