Theta Ophiuchi,
Latinized from θ Ophiuchi, is a
multiple star system in the
equatorialconstellation of
Ophiuchus. It lies on the "right foot" of the serpent-bearer, just southwest of
Kepler's Star, the nova of 1604. According to Richard H. Allen's Star Names: Their Lore and Meaning (1899), θ Oph together with
ξ Oph formed the Sogdian Wajrik "the Magician", the Khorasmian Markhashik "the Serpent-bitten" and with
η Oph the Coptic Tshiō, "the Snake", and Aggia, "the Magician".[12] This star has an
apparent visual magnitude of +3.3,[6] making it
readily visible to the naked eye. Based upon
parallax measurements from the
Hipparcos mission, it is roughly 436
light-years (134
parsecs) from Earth.[1] It is 1.8 degrees south of the ecliptic and therefore subject to
lunaroccultations and less frequently occulted by a planet.
The primary component of this system is a
variable star of the
Beta Cephei type with a period of just 3h 22m.[15] It has nearly nine[3] times the mass of the Sun and more than six[7] times the Sun's radius. Although only 21 million years old,[3] it has begun to
evolve away from the
main sequence and has become a
subgiant star with a
stellar classification of B2 IV.[3] This massive star is radiating around 5,000 times the luminosity of the Sun from its outer atmosphere at an
effective temperature of about 22,260 K,[8] giving it the blue-white hue of a
B-type star.[16]
^
abJohnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99,
Bibcode:
1966CoLPL...4...99J
^Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick (eds.), "The Revision of the General Catalogue of Radial Velocities", Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, vol. 30, University of Toronto:
International Astronomical Union, p. 57,
Bibcode:
1967IAUS...30...57E
^
abcdde Geus, E. J.; de Zeeuw, P. T.; Lub, J. (June 1989), "Physical parameters of stars in the Scorpio-Centaurus OB association", Astronomy and Astrophysics, 216 (1–2): 44–61,
Bibcode:
1989A&A...216...44D
^
abUnderhill, A. B.; et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society, 189 (3): 601–605,
Bibcode:
1979MNRAS.189..601U,
doi:10.1093/mnras/189.3.601
^"The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from
the original on 2013-12-03, retrieved 2012-01-16