Theta Ceti

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Theta Ceti
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cetus
Right ascension  01h 24m 01.40528s[1]
Declination −08° 10′ 59.7212″[1]
Apparent magnitude (V) 3.60[2]
Spectral type K0 III[3]
B−V color index +1.07[2]
Radial velocity (Rv)+17.2±0.5[4] km/s
Proper motion (μ) RA: −77.94[1] mas/yr
Dec.: −206.53[1] mas/yr
Parallax (π)28.66 ± 0.19[1] mas
Distance113.8 ± 0.8 ly
(34.9 ± 0.2 pc)
Absolute magnitude (MV)+0.89[5]
Mass1.80[6] M
Radius10.04 R
Luminosity53 L
Surface gravity (log g)2.70 cgs
Temperature4,660±17[6] K
Metallicity [Fe/H]−0.13±0.15 dex
Rotational velocity (v sin i)2.60 km/s
Age2.20[6] Gyr
Other designations
θ Cet, 45 Cet, BD+08° 244, FK5 47, HD 8512, HIP 6537, HR 402, SAO 129274[7]
Database references

Theta Ceti, Latinized from θ Ceti, is a solitary,[8] orange-hued star in the equatorial constellation of Cetus. It is visible to the naked eye with an apparent visual magnitude of 3.60.[2] Based upon an annual parallax shift of 28.66 mas as seen from Earth,[1] it is located about 114 light years from the Sun. At that distance, the visual magnitude is diminished by an extinction factor of 0.10 due to interstellar dust.[2]

With an age of about 2.2 billion years,[6] this is an evolved, K-type giant star with a stellar classification of K0 III.[3] It is a red clump[9] star on the horizontal branch,[2] which means it is generating energy through helium fusion at its core.[9] The star has an estimated 1.8[6] times the mass of the Sun and has expanded to 10 times the Sun's radius.[2] It is radiating 53[2] times the solar luminosity from its photosphere at an effective temperature of 4,660 K.[6]


In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Thanih al Naamat (ثاني النعامات - thānī al-naʽāmāt), which was translated into Latin as Secunda Struthionum, meaning the second ostrich.[10] This star, along with η Cet (Deneb Algenubi), τ Cet (Thalath Al Naamat), ζ Cet (Baten Kaitos)and υ Cet, were Al Naʽāmāt (النعامات), the Hen Ostriches.[11][12]

In Chinese, 天倉 (Tiān Cāng), meaning Square Celestial Granary, refers to an asterism consisting of θ Ceti, ι Ceti, η Ceti, ζ Ceti, τ Ceti and 57 Ceti.[13] Consequently, the Chinese name for θ Ceti itself is 天倉三 (Tiān Cāng sān, English: the Third Star of Square Celestial Granary.)[14]


  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. ^ a b c d e f g h Jones, M. I.; et al. (December 2011), "Study of the impact of the post-MS evolution of the host star on the orbits of close-in planets. I. Sample definition and physical properties", Astronomy & Astrophysics, 536: 7, arXiv:1110.6459, Bibcode:2011A&A...536A..71J, doi:10.1051/0004-6361/201117887, A71.
  3. ^ a b Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, Ann Arbor, Michigan: Department of Astronomy, University of Michigan, 5, Bibcode:1999MSS...C05....0H.
  4. ^ de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, A61.
  5. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  6. ^ a b c d e f Luck, R. Earle (2015), "Abundances in the Local Region. I. G and K Giants", Astronomical Journal, 150 (3), 88, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88.
  7. ^ "tet Cet -- Horizontal Branch Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-04-25.
  8. ^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  9. ^ a b Laney, C. D.; et al. (January 2012), "A new Large Magellanic Cloud K-band distance from precision measurements of nearby red clump stars", Monthly Notices of the Royal Astronomical Society, 419 (2): 1637–1641, arXiv:1109.4800, Bibcode:2012MNRAS.419.1637L, doi:10.1111/j.1365-2966.2011.19826.x.
  10. ^ 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: 429, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429.
  11. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc, p. 162, ISBN 0-486-21079-0, retrieved 2017-04-26.
  12. ^ η Cet as Aoul al Naamat or Prima Struthionum (the first ostrich), θ Cet as Thanih al Naamat or Secunda Struthionum (the second ostrich), τ Cet as Thalath al Naamat or Tertia Struthionum (the third ostrich), and ζ Cet as Rabah al Naamat or Quarta Struthionum (the fourth ostrich). υ Cet should be Khamis al Naamat or Quinta Struthionum (the fifth ostrich) consistently, but Al Achsasi Al Mouakket designated the title the fifth ostrich to γ Gam with uncleared consideration.
  13. ^ (in 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.
  14. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 10 日