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Eta Ophiuchi A/B
Observation data
Epoch J2000      Equinox J2000
Constellation Ophiuchus
Right ascension 17h 10m 22.7s
Declination -15° 43′ 29.7″
Apparent magnitude (V) 2.43 (3.0/3.5)
Characteristics
Spectral type A2.5 Va/A3 V
U-B color index 0.09
B-V color index 0.05
Variable type ?
Astrometry
Radial velocity (Rv) -2.4 km/s
Proper motion (μ) RA: 41.16 mas/yr
Dec.: 97.65 mas/yr
Parallax (π) 38.77 ± 0.86 mas
Distance 84.1 ly
(25.79 pc)
Absolute magnitude (MV) 0.37
Details
Mass 2.3/2.0 M
Radius 2.5/2.0 R
Luminosity 35/21 L
Temperature 8900/8600 K
Metallicity ?
Rotation 30 km/s.
Age ? years
Other designations
35 Oph, Gl 656.1A/B, HD 155125, HR 6378, BD -15°4467, GCTP 3895.00, SAO 160332, HIP 84012
Database references
SIMBAD data

Eta Ophiuchi (η Oph / η Ophiuchi) is a star in the constellation Ophiuchus. It also 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 warmer 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 very fast and highly elliptical orbit, making planetary formation impossible in this system and some stellar data imprecise.

η Oph is the northern pole star of the planet Uranus.

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