Delta Hydrae

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Delta Hydrae
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Hydra
Right ascension 8h 37m 39.4s
Declination 5° 42′ 13″
Apparent magnitude (V) 4.14
Distance 179 ly
(54.91 pc)
Spectral type A1V
Other designations
4 Hydrae, BD+06 2001, FK5 1223, HD 73262, HIP 42313, HR 3410, SAO 116965.[1]

Delta Hydrae (δ Hya, δ Hydrae) is a Class A1, fourth-magnitude star in the constellation Hydra. Delta Hydrae is a binary double star, located about 180 light-years from Earth. It has 2.2 times the mass of the Sun, 1.5 times the Sun's radius and is radiating 17 times the luminosity of the Sun.[2]

Name and etymology[edit]

In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Lisan al Shudja, which was translated into Latin as Lingua Hydri, meaning the snake's tongue.[3] This star, along with ε Hya, ζ Hya, η Hya, ρ Hya and σ Hya (Minhar al Shija), were Ulugh Beg's Min al Azʽal, "Belonging to the Uninhabited Spot".[4]

According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Min al Azʽal or Minazal were the title for five stars :δ Hya as Minazal I, η Hya as Minazal II, ε Hya as Minazal III, ρ Hya as Minazal IV and ζ Hya as Minazal V (exclude σ Hya)[5]

In Chinese, 柳宿 (Liǔ Sù), meaning Willow (asterism), refers to an asterism consisting of δ Hydrae, σ Hydrae, η Hydrae, ρ Hydrae, ε Hydrae, ζ Hydrae, ω Hydrae and θ Hydrae[6] Consequently, δ Hydrae itself is known as 柳宿一 (Liǔ Sù yī, English: the First Star of Willow.)[7]

The people of Groote Eylandt called Unwala, "The Crab", for the star cluster including this star, ε Hya, ζ Hya, η Hya, ρ Hya and σ Hya (Minhar al Shija).[8]


  1. ^ "HD 73262 -- Variable Star". SIMBAD Astronomical Database. Retrieved 2006-11-05. 
  2. ^ Malagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M 
  3. ^ 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. 
  4. ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 249. ISBN 0-486-21079-0. Retrieved 2010-12-12. 
  5. ^ Jack W. Rhoads - Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars, Jet Propulsion Laboratory, California Institute of Technology; November 15, 1971
  6. ^ (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.
  7. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 28 日
  8. ^ Helaine Selin, ed., Encyclopaedia of the history of science, technology, and medicine in non-western cultures, Dordrecht, Kluwer Academic Publishers, 1997, p.105.