Epoch J2000 Equinox J2000
|Right ascension||05h 24m 28.61672s|
|Declination||–02° 23′ 49.7311″|
|Apparent magnitude (V)||3.42|
|Spectral type||B1 V + B3 V + B2 V|
|U−B color index||–0.90|
|B−V color index||−0.17|
|Radial velocity (Rv)||+19.8 km/s|
|Proper motion (μ)||RA: −0.71 mas/yr
Dec.: −3.46 mas/yr
|Parallax (π)||3.34 ± 1.07 mas|
|Distance||approx. 1,000 ly
(approx. 300 pc)
|η Ori A|
|Mass||20 M☉|
|Radius||10 R☉|
|Luminosity||38,000 L☉|
|Rotational velocity (v sin i)||60 km/s|
|η Ori B|
|Rotational velocity (v sin i)||45 km/s|
Eta Orionis (η Ori, η Orionis) is a star in the constellation Orion. Other names are Saiph (Arabic for "sword"), Algjebbah (Arabic for "scutum"), and Ensis (Latin for "sword", since the star is taken to represent Orion's sheathed weapon). Eta Orionis lies a little to the west of Orion's belt between Delta Orionis and Rigel, being closer to Delta Orionis than to Rigel. It lies at a distance of around 1,000 light years from Earth and is part of the Orion Arm.
This is a quadruple star system, of which three members can be resolved with a telescope. The primary component is an eclipsing binary star in a triple-star grouping. These stars have orbital periods of 8 days and 9.2 years. It includes a variable star with a pulsation period of around 8 hours. Three of the components are B-type main sequence stars with stellar classifications of B1 V, B3 V and B2 V.
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- Crawford, D. L.; Barnes, J. V.; Golson, J. C. (1971), "Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere", The Astronomical Journal, 76: 1058, Bibcode:1971AJ.....76.1058C, doi:10.1086/111220
- Zasche, P.; et al. (August 2009), "A Catalog of Visual Double and Multiple Stars With Eclipsing Components", The Astronomical Journal, 138 (2): 664–679, arXiv:, Bibcode:2009AJ....138..664Z, doi:10.1088/0004-6256/138/2/664
- AAVSO International Variable Star Index VSX (Watson+, 2006-2012) VizieR
- Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, eds., The Revision of the General Catalogue of Radial Velocities, University of Toronto: International Astronomical Union, retrieved 2009-09-10
- Levato, H. (January 1975), "Rotational velocities and spectral types for a sample of binary systems", Astronomy and Astrophysics Supplement Series, 19: 91–99, Bibcode:1975A&AS...19...91L
- "CCDM J05245-0223AB -- Double or multiple star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-02-09
- Allen, R. H. (1899). Star-Names and Their Meanings. New York: G. E. Stechert. p. 316.
Saiph was also used to indicate Kappa Orionis in the same constellation.
- Moore, P. (1983). The Guinness Book of Astronomy: Facts and Feats (2nd ed.). Middlesex: Guinness Superlatives Limited. p. 230.
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