Theta Cancri

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Theta Cancri
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cancer
Right ascension  08h 31m 35.73082s[1]
Declination +18° 05′ 39.9166″[1]
Apparent magnitude (V) +5.323[2]
Spectral type K5 III[3]
U−B color index +1.949[2]
B−V color index +1.565[2]
Radial velocity (Rv)+44.47±0.19[4] km/s
Proper motion (μ) RA: −60.438[1] mas/yr
Dec.: −57.331[1] mas/yr
Parallax (π)7.3204 ± 0.1826[1] mas
Distance450 ± 10 ly
(137 ± 3 pc)
Absolute magnitude (MV)−0.19[5]
[1] R
Luminosity353.1±10.1[1] L
[1] K
Other designations
θ Cnc, 31 Cancri, BD+18° 1963, FK5 2667, HD 72094, HIP 41822, HR 3357, SAO 97881[6]
Database references

Theta Cancri, Latinized from θ Cancri, is a multiple star[7][3] system in the zodiac constellation of Cancer. It is visible to the naked eye as a dim point of light with an apparent visual magnitude of +5.32.[2] The system is located at a distance of approximately 450 light years away from the Sun, based on parallax,[1] and is drifting further away with a radial velocity of +44 km/s.[4] Since it is near the ecliptic, it can be occulted by the Moon[8] and, very rarely, by planets.

The primary, designated component A, is K-type giant star with a stellar classification of K5 III,[3] having exhausted the supply of hydrogen at its core, then cooled and expanded. At present it has 40[1] times the girth of the Sun. It is radiating 353[1] times the luminosity of the Sun at an effective temperature of 3,955 K.[1]

In Chinese astronomy, Ghost (Chinese: 鬼宿; pinyin: Guǐ Xiù) refers to an asterism consisting of Theta Cancri, Eta Cancri, Gamma Cancri and Delta Cancri.[9] Theta Cancri is the first star of Ghost (Chinese: 鬼宿一; pinyin: Guǐ Xiù yī), as it is also the determinative star for that asterism.[10]


  1. ^ a b c d e f g h i j k l Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. ^ a b c d Gutierrez-Moreno, Adelina; et al. (1966), "A System of photometric standards", Publications of the Department of Astronomy University of Chile, Publicaciones Universidad de Chile, Department de Astronomy, 1: 1–17, Bibcode:1966PDAUC...1....1G.
  3. ^ a b c 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.
  4. ^ a b 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. ^ "tet Cnc -- Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-06-19.
  7. ^ Hartkopf, W. I.; McAlister, H. A. (January 1984), "Binary stars unresolved by speckle interferometry. III", Publications of the Astronomical Society of the Pacific, 96: 105–116, Bibcode:1984PASP...96..105H, doi:10.1086/131309.
  8. ^ White, Nathaniel M.; Feierman, Barry H. (September 1987), "A Catalog of Stellar Angular Diameters Measured by Lunar Occultation", Astronomical Journal, 94: 751, Bibcode:1987AJ.....94..751W, doi:10.1086/114513.
  9. ^ 陳久金 (2005). Zhōngguó Xīngzuò Shénhuà 中國星座神話 [Chinese Constellation Mythology]. 台灣古籍出版有限公司. p. 394. ISBN 978-986-7332-25-7.
  10. ^ 陳久金 (2005). Zhōngguó Xīngzuò Shénhuà 中國星座神話 [Chinese Constellation Mythology]. 台灣古籍出版有限公司. p. 193. ISBN 978-986-7332-25-7.