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Orion constellation map.svg
Red circle.svg

Location of Saiph (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Orion
Right ascension 05h 47m 45.38884s[1]
Declination −09° 40′ 10.5777″[1]
Apparent magnitude (V) 2.09[2]
Spectral type B0.5 Ia[3]
U−B color index –1.02[2]
B−V color index –0.18[2]
Variable type Suspected[4]
Radial velocity (Rv) +20.5[5] km/s
Proper motion (μ) RA: +1.46[1] mas/yr
Dec.: –1.28[1] mas/yr
Parallax (π) 5.04 ± 0.22[1] mas
Distance 650 ± 30 ly
(198 ± 9 pc)
Absolute magnitude (MV) –6.1[6]
Mass 15.50 ± 1.25[7] M
Radius 22.2[6] R
Luminosity 56,881[7] L
Surface gravity (log g) 2.9[6] cgs
Temperature 26,500[6] K
Rotational velocity (v sin i) 83[6] km/s
Age 11.1 ± 0.5[8] Myr
Other designations
κ Orionis, 53 Orionis, 141 G. Orionis, BD–09 1235, FK5 220, HD 38771, HIP 27366, HR 2004, SAO 132542.[9]
Database references

Saiph, also designated Kappa Orionis (κ Orionis, abbreviated Kappa Ori, κ Ori) and 53 Orionis (53 Ori), is the sixth-brightest star in the constellation of Orion. Of the four bright stars that compose Orion's main quadrangle, it is the star at the south-eastern corner. A northern-hemisphere observer facing south would see it at the lower left of Orion, and a southern-hemisphere observer facing north would see it at the upper right. Parallax measurements yield an estimated distance of 650 light-years (198 parsecs) from the Sun, which is about the same as Betelgeuse.[1] However, despite being a hotter star, it is smaller and less luminous than Rigel with an apparent visual magnitude of 2.1.[2] The luminosity of this star changes slightly, varying by 0.04 magnitudes.[4]


Kappa Orionis is the star's Bayer designation and 53 Orionis its Flamsteed designation. The traditional name Saiph is from the Arabic saif al jabbar, 'سیف الجبّار' literally sword of the giant. This name was originally applied to Eta Orionis.[10] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[11] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[12] included a table of the first two batches of names approved by the WGSN; which included Saiph for this star. It is now so entered in the IAU Catalog of Star Names.[13]

In the 17th century catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Rekbah al Jauza al Yemeniat, which was translated into Latin as Genu Dextrum Gigantis "right knee of the giant".[14]


Saiph has a stellar classification of B0.5 Ia. The luminosity class 'Ia' represents a bright supergiant star that has exhausted the supply of hydrogen at its core and evolved away from the main sequence. Saiph has a strong stellar wind and is losing mass at the rate of 9.0 × 10−7 times the mass of the Sun per year, or the equivalent of the Sun's mass every 1.1 million years.[6] Using a combination of parallax as determined by HIPPARCOS and spectrum yields a mass 15.50 ± 1.25 times and luminosity 56,881 times that of the Sun.[7] Analysis of the spectra and age of the members of the Orion OB1 association yields a mass 28 times that of the Sun (from an original mass 31.8 times that of the Sun) and an age of 6.2 million years.[15] Large stars such as Saiph (and many other stars in Orion) are destined to collapse on themselves and explode as supernovae.[16]

Cultural significance[edit]

The Wardaman people of northern Australia know Saiph as the Guman digging stick, used to make a canyon by Black-headed Python.[17]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c d 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 
  3. ^ Morgan, W. W.; Keenan, P. C. (1973). "Spectral Classification". Annual Review of Astronomy and Astrophysics. 11: 29. Bibcode:1973ARA&A..11...29M. doi:10.1146/annurev.aa.11.090173.000333. 
  4. ^ a b Lefèvre, L.; et al. (November 2009), "A systematic study of variability among OB-stars based on HIPPARCOS photometry", Astronomy and Astrophysics, 507 (2): 11411201, Bibcode:2009A&A...507.1141L, doi:10.1051/0004-6361/200912304 
  5. ^ Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, Astronomisches Rechen-Institut Heidelberg, 35 (35), Bibcode:1999VeARI..35....1W 
  6. ^ a b c d e f Crowther, P. A.; Lennon, D. J.; Walborn, N. R. (January 2006), "Physical parameters and wind properties of galactic early B supergiants", Astronomy and Astrophysics, 446 (1): 279–293, arXiv:astro-ph/0509436Freely accessible, Bibcode:2006A&A...446..279C, doi:10.1051/0004-6361:20053685 
  7. ^ a b c Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten, 331 (4): 349, arXiv:1003.2335Freely accessible, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355 
  8. ^ Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883Freely accessible, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x 
  9. ^ "SAIPH -- Variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-12 
  10. ^ Allen, Richard Hinckley (1899). Star-names and their meanings. G. E. Stechert. p. 317. 
  11. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016. 
  12. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016. 
  13. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  14. ^ 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. 
  15. ^ Voss, R.; Diehl, R.; Vink, J. S.; Hartmann, D. H. (2010). "Probing the evolving massive star population in Orion with kinematic and radioactive tracers". Astronomy and Astrophysics. 520: 10. arXiv:1005.3827Freely accessible. Bibcode:2010A&A...520A..51V. doi:10.1051/0004-6361/201014408. A51. 
  16. ^ Kaler, James B., "SAIPH (Kappa Orionis)", Stars, University of Illinois, retrieved 2012-01-27 
  17. ^ Harney, Bill Yidumduma; Cairns, Hugh C. (2004) [2003]. Dark Sparklers (Revised ed.). Merimbula, New South Wales: Hugh C. Cairns. p. 139. ISBN 0-9750908-0-1. 

Coordinates: Sky map 05h 47m 45.4s, −09° 40′ 11″