# Zeta Hydrae

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Star in the constellation Hydra

ζ Hydrae Location of ζ Hydrae (circled) Observation data Epoch J2000.0 Equinox J2000.0 Constellation Hydra Right ascension 08h 55m 23.62614s[1] Declination +05° 56′ 44.0354″[1] Apparent magnitude (V) 3.10[2] Characteristics Spectral type G9 II-III[3] U−B color index +0.82[2] B−V color index +1.00[2] Astrometry Radial velocity (Rv) +22.8[4] km/s Proper motion (μ) RA: –100.06[1] mas/yr Dec.: +15.46[1] mas/yr Parallax (π) 19.51±0.18 mas[1] Distance 167 ± 2 ly (51.3 ± 0.5 pc) Absolute magnitude (MV) –0.24[5] Details[6] Mass 3.09±0.1 M☉ Radius 17.61±0.19 R☉ Luminosity 174.2±9.3 L☉ Surface gravity (log g) 2.48[7] cgs Temperature 4,996±30 K Metallicity [Fe/H] –0.21[8] dex Rotational velocity (v sin i) 2.5[8] km/s Age 370±40 Myr Other designations 16 Hydrae, BD+06 2060, FK5 334, HD 76294, HIP 43813, HR 3547, SAO 117264[9] Database references SIMBAD data

**Zeta Hydrae** (ζ Hya, ζ Hydrae) is a solitary [star](/source/Star) in the [equatorial](/source/Celestial_equator) [constellation](/source/Constellation) of [Hydra](/source/Hydra_(constellation)). This is a generally faint constellation, so, at an [apparent visual magnitude](/source/Apparent_visual_magnitude) of +3.10,[2] this is the [third-brightest member](/source/List_of_stars_in_Hydra) after [Alphard](/source/Alphard) and [Naga](/source/Gamma_Hydrae).

## Distance

The distance to this star has been measured using the [parallax](/source/Parallax) technique, yielding a value of roughly 167 [light-years](/source/Light-year) (51 [parsecs](/source/Parsec)).[1] At this distance, the [visual magnitude](/source/Visual_magnitude) of the star is diminished by 0.03 as a result of [extinction](/source/Extinction_(astronomy)) from intervening gas and dust.[5] [Delta Hydrae](/source/Delta_Hydrae) is about 12.9 light-years (4.0 parsecs) from Zeta Hydrae and may be a largely co-moving object.[10] The star has one of the lower-error margin readings among those of the [Gaia spacecraft](/source/Gaia_spacecraft) which computes a parallax of 20.7182 ± 0.3925 mas and, if correct, a distance of 157 ± 3 light years.[11]

## Characteristics

With a [stellar classification](/source/Stellar_classification) of G9 II-III,[3] this is an [evolved](/source/Stellar_evolution) [giant star](/source/Giant_star) that is radiating 174 times the [luminosity of the Sun](/source/Solar_luminosity) from its [outer envelope](/source/Stellar_atmosphere) at an [effective temperature](/source/Effective_temperature) of around 5,000 K.[6] At this heat, the star glows with the yellow hue of a [G-type star](/source/Stellar_classification#Class_G).[12] The radius of this star, measured using [interferometry](/source/Interferometry), is 17.6 times the Sun's radius. It has an estimated 3.1 times the mass of the Sun and is around 370 million years old.[6]

## Name and etymology

This star, along with [δ Hya](/source/Delta_Hydrae) (Lisan al Sudja), [ε Hya](/source/Epsilon_Hydrae), [η Hya](/source/Eta_Hydrae), [ρ Hya](/source/Rho_Hydrae) and [σ Hya](/source/Sigma_Hydrae) (Minchir), were Ulug Beg's *Min al Azʽal*, "Belonging to the Uninhabited Spot".[13] 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](/source/Delta_Hydrae) as *Minazal I*, [η Hya](/source/Eta_Hydrae) as *Minazal II*, [ε Hya](/source/Epsilon_Hydrae) as *Minazal III*, [ρ Hya](/source/Rho_Hydrae) as *Minazal IV* and ζ Hya as *Minazal V* (exclude [σ Hya](/source/Sigma_Hydrae)).[14]

In [Chinese](/source/Chinese_language), 柳宿 (*Liǔ Sù*), meaning *[Willow](/source/Willow_(Chinese_constellation))*, refers to an [asterism](/source/Asterism_(astronomy)) consisting of ζ Hydrae, [δ Hydra](/source/Delta_Hydrae), [σ Hydrae](/source/Sigma_Hydrae), [η Hydrae](/source/Eta_Hydrae), [ρ Hydrae](/source/Rho_Hydrae), [ε Hydrae](/source/Epsilon_Hydrae), [ω Hydrae](/source/Omega_Hydrae) and [θ Hydrae](/source/Theta_Hydrae)[15] Consequently, ζ Hydrae itself is known as 柳宿六 (*Liǔ Sù liù*, English: the Sixth Star of Willow).[16]

The people of [Groote Eylandt](/source/Groote_Eylandt) called *Unwala*, "The Crab", for the star cluster including this star, [δ Hya](/source/Delta_Hydrae) (Lisan al Sudja), [ε Hya](/source/Epsilon_Hydrae) (Ashlesha), [η Hya](/source/Eta_Hydrae), [ρ Hya](/source/Rho_Hydrae) and [σ Hya](/source/Sigma_Hydrae) (Minchir).[17]

## References

1. ^ [***a***](#cite_ref-aaa474_2_653_1-0) [***b***](#cite_ref-aaa474_2_653_1-1) [***c***](#cite_ref-aaa474_2_653_1-2) [***d***](#cite_ref-aaa474_2_653_1-3) [***e***](#cite_ref-aaa474_2_653_1-4) [***f***](#cite_ref-aaa474_2_653_1-5) van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", *Astronomy and Astrophysics*, **474** (2): 653–664, [arXiv](/source/ArXiv_(identifier)):[0708.1752](https://arxiv.org/abs/0708.1752), [Bibcode](/source/Bibcode_(identifier)):[2007A&A...474..653V](https://ui.adsabs.harvard.edu/abs/2007A&A...474..653V), [doi](/source/Doi_(identifier)):[10.1051/0004-6361:20078357](https://doi.org/10.1051%2F0004-6361%3A20078357), [S2CID](/source/S2CID_(identifier)) [18759600](https://api.semanticscholar.org/CorpusID:18759600)

1. ^ [***a***](#cite_ref-mnras172_667_2-0) [***b***](#cite_ref-mnras172_667_2-1) [***c***](#cite_ref-mnras172_667_2-2) [***d***](#cite_ref-mnras172_667_2-3) Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants.", *[Monthly Notices of the Royal Astronomical Society](/source/Monthly_Notices_of_the_Royal_Astronomical_Society)*, **172** (3): 667–679, [Bibcode](/source/Bibcode_(identifier)):[1975MNRAS.172..667J](https://ui.adsabs.harvard.edu/abs/1975MNRAS.172..667J), [doi](/source/Doi_(identifier)):[10.1093/mnras/172.3.667](https://doi.org/10.1093%2Fmnras%2F172.3.667)

1. ^ [***a***](#cite_ref-araa11_29_3-0) [***b***](#cite_ref-araa11_29_3-1) Morgan, W. W.; Keenan, P. C. (1973), "Spectral Classification", *Annual Review of Astronomy and Astrophysics*, **11** (1): 29–50, [Bibcode](/source/Bibcode_(identifier)):[1973ARA&A..11...29M](https://ui.adsabs.harvard.edu/abs/1973ARA&A..11...29M), [doi](/source/Doi_(identifier)):[10.1146/annurev.aa.11.090173.000333](https://doi.org/10.1146%2Fannurev.aa.11.090173.000333)

1. **[^](#cite_ref-scfs_4-0)** Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", *Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg*, **35** (35), Astronomisches Rechen-Institut Heidelberg: 1, [Bibcode](/source/Bibcode_(identifier)):[1999VeARI..35....1W](https://ui.adsabs.harvard.edu/abs/1999VeARI..35....1W)

1. ^ [***a***](#cite_ref-pasj60_4_781_5-0) [***b***](#cite_ref-pasj60_4_781_5-1) Takeda, Yoichi; Sato, Bun'ei; Murata, Daisuke (August 2008), "Stellar parameters and elemental abundances of late-G giants", *Publications of the Astronomical Society of Japan*, **60** (4): 781–802, [arXiv](/source/ArXiv_(identifier)):[0805.2434](https://arxiv.org/abs/0805.2434), [Bibcode](/source/Bibcode_(identifier)):[2008PASJ...60..781T](https://ui.adsabs.harvard.edu/abs/2008PASJ...60..781T), [doi](/source/Doi_(identifier)):[10.1093/pasj/60.4.781](https://doi.org/10.1093%2Fpasj%2F60.4.781), [S2CID](/source/S2CID_(identifier)) [16258166](https://api.semanticscholar.org/CorpusID:16258166)

1. ^ [***a***](#cite_ref-Baines2018_6-0) [***b***](#cite_ref-Baines2018_6-1) [***c***](#cite_ref-Baines2018_6-2) Baines, Ellyn K.; et al. (2018), "Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer", *The Astronomical Journal*, **155** (1), 30, [arXiv](/source/ArXiv_(identifier)):[1712.08109](https://arxiv.org/abs/1712.08109), [Bibcode](/source/Bibcode_(identifier)):[2018AJ....155...30B](https://ui.adsabs.harvard.edu/abs/2018AJ....155...30B), [doi](/source/Doi_(identifier)):[10.3847/1538-3881/aa9d8b](https://doi.org/10.3847%2F1538-3881%2Faa9d8b), [S2CID](/source/S2CID_(identifier)) [119427037](https://api.semanticscholar.org/CorpusID:119427037).

1. **[^](#cite_ref-pasj62_4_1117_7-0)** Ando, Hiroyasu; Tsuboi, Yusuke; Kambe, Eiji; Sato, Bun'ei (August 2010), "Oscillations in G-Type Giants", *Publications of the Astronomical Society of Japan*, **62** (4): 1117–1126, [arXiv](/source/ArXiv_(identifier)):[1007.1286](https://arxiv.org/abs/1007.1286), [Bibcode](/source/Bibcode_(identifier)):[2010PASJ...62.1117A](https://ui.adsabs.harvard.edu/abs/2010PASJ...62.1117A), [doi](/source/Doi_(identifier)):[10.1093/pasj/62.4.1117](https://doi.org/10.1093%2Fpasj%2F62.4.1117), [S2CID](/source/S2CID_(identifier)) [118677219](https://api.semanticscholar.org/CorpusID:118677219)

1. ^ [***a***](#cite_ref-aj135_1_209_8-0) [***b***](#cite_ref-aj135_1_209_8-1) Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", *The Astronomical Journal*, **135** (1): 209–231, [Bibcode](/source/Bibcode_(identifier)):[2008AJ....135..209M](https://ui.adsabs.harvard.edu/abs/2008AJ....135..209M), [doi](/source/Doi_(identifier)):[10.1088/0004-6256/135/1/209](https://doi.org/10.1088%2F0004-6256%2F135%2F1%2F209), [S2CID](/source/S2CID_(identifier)) [121883397](https://api.semanticscholar.org/CorpusID:121883397)

1. **[^](#cite_ref-SIMBAD_9-0)** ["zet Hya"](http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=zet+Hya). *[SIMBAD](/source/SIMBAD)*. [Centre de données astronomiques de Strasbourg](/source/Centre_de_donn%C3%A9es_astronomiques_de_Strasbourg). Retrieved 2006-11-05.

1. **[^](#cite_ref-apjss192_1_2_10-0)** Shaya, Ed J.; Olling, Rob P. (January 2011), "Very Wide Binaries and Other Comoving Stellar Companions: A Bayesian Analysis of the Hipparcos Catalogue", *The Astrophysical Journal Supplement*, **192** (1): 2, [arXiv](/source/ArXiv_(identifier)):[1007.0425](https://arxiv.org/abs/1007.0425), [Bibcode](/source/Bibcode_(identifier)):[2011ApJS..192....2S](https://ui.adsabs.harvard.edu/abs/2011ApJS..192....2S), [doi](/source/Doi_(identifier)):[10.1088/0067-0049/192/1/2](https://doi.org/10.1088%2F0067-0049%2F192%2F1%2F2), [S2CID](/source/S2CID_(identifier)) [119226823](https://api.semanticscholar.org/CorpusID:119226823)

1. **[^](#cite_ref-dr2_11-0)** [Brown, A. G. A.](/source/Anthony_Brown_(scientist)); et al. ([Gaia collaboration](/source/Data_Processing_and_Analysis_Consortium)) (August 2018). ["*Gaia* Data Release 2: Summary of the contents and survey properties"](https://doi.org/10.1051%2F0004-6361%2F201833051). *[Astronomy & Astrophysics](/source/Astronomy_%26_Astrophysics)*. **616**. A1. [arXiv](/source/ArXiv_(identifier)):[1804.09365](https://arxiv.org/abs/1804.09365). [Bibcode](/source/Bibcode_(identifier)):[2018A&A...616A...1G](https://ui.adsabs.harvard.edu/abs/2018A&A...616A...1G). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/201833051](https://doi.org/10.1051%2F0004-6361%2F201833051). [Gaia DR2 record for this source](https://vizier.u-strasbg.fr/viz-bin/VizieR-S?Gaia%20DR2%2020583588100208201984) at [VizieR](/source/VizieR).

1. **[^](#cite_ref-csiro_12-0)** ["The Colour of Stars"](https://web.archive.org/web/20131203222826/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html), *Australia Telescope, Outreach and Education*, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from [the original](http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html) on 2013-12-03, retrieved 2012-01-16

1. **[^](#cite_ref-allen1963_13-0)** [Allen, R. H.](/source/Richard_Hinckley_Allen) (1963), [*Star Names: Their Lore and Meaning*](https://archive.org/details/starnamestheirlo00alle/page/249) (Reprint ed.), New York, NY: Dover Publications Inc, p. [249](https://archive.org/details/starnamestheirlo00alle/page/249), [ISBN](/source/ISBN_(identifier)) [0-486-21079-0](https://en.wikipedia.org/wiki/Special:BookSources/0-486-21079-0), retrieved 2010-12-12 {{[citation](https://en.wikipedia.org/wiki/Template:Citation)}}: ISBN / Date incompatibility ([help](https://en.wikipedia.org/wiki/Help:CS1_errors#invalid_isbn_date))

1. **[^](#cite_ref-rhoads1971_14-0)** Rhoads, Jack W. (November 15, 1971), [*Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars*](https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720005197_1972005197.pdf) (PDF), Jet Propulsion Laboratory, California Institute of Technology

1. **[^](#cite_ref-15)** (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](/source/ISBN_(identifier)) [978-986-7332-25-7](https://en.wikipedia.org/wiki/Special:BookSources/978-986-7332-25-7).

1. **[^](#cite_ref-16)** (in Chinese) [AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 28 日](http://aeea.nmns.edu.tw/2006/0605/ap060528.html) [Archived](https://web.archive.org/web/20110522112415/http://aeea.nmns.edu.tw/2006/0605/ap060528.html) 2011-05-22 at the [Wayback Machine](/source/Wayback_Machine)

1. **[^](#cite_ref-selin1997_17-0)** [Selin, Helaine](/source/Helaine_Selin), ed. (1997), [*Encyclopaedia of the history of science, technology, and medicine in non-western cultures*](https://books.google.com/books?id=raKRY3KQspsC), Dordrecht: Kluwer Academic Publishers, p. 105, [ISBN](/source/ISBN_(identifier)) [9780792340669](https://en.wikipedia.org/wiki/Special:BookSources/9780792340669)

v t e Constellation of Hydra List of stars in Hydra Hydra in Chinese astronomy Stars Bayer α (Alphard) β γ (Naga) δ ε (Ashlesha) ζ η θ ι (Ukdah) κ λ μ ν ξ ο π ρ σ (Minchir) τ1 τ2 υ1 (Zhang) υ2 φ1 φ2 φ3 χ1 χ2 ψ ω b1 b3 C F Flamsteed 1 2 3 6 (a) 9 10 12 (D) 14 15 17 19 20 21 23 24 25 26 27 (P) 28 29 33 (A) 34 37 44 47 48 50 51 (k) 52 (l) 54 (m) 55 56 57 58 (Solitaire) 59 60 10 Crt 17 Crt 20 Crt 2 Sex Variable R U V W TW EX HS KU LQ V361 V419 V421 V478 V484 HR 3378 3538 3749 (G) 3750 3858 (I) 3862 3919 3923 (Felis) 4162 4328 4339 (β Ant) 4445 5265 HD 72659 74156 82943 86226 86264 90156 (γ Ant) Other 2MASS 1114−2618 ESO 439-26 Gliese 328 Gliese 357 Gliese 433 Gliese 453 GJ 3634 HAT-P-30 HE 1256−2738 HE 1327−2326 LHS 2065 LHS 3003 LTT 3780 SDSS J090745.0+024507 WASP-25 WASP-36 WASP-84 WASP-166 (Filetdor) WISE 0855−0714 WISEA J1141−3326 Exoplanets Gliese 357 d HD 72659 b HD 74156 b c HD 82943 b c HD 86226 b HD 86264 b TW Hydrae b (unconfirmed) WASP-193b Star clusters Messier 48 Messier 68 NGC 5694 Price-Whelan 1 Nebulae Abell 33 Abell 35 NGC 3242 Southern Owl Nebula Galaxies Messier 83 NGC 2617 2642 2697 2708 2758 2835 2848 2865 2890 2935 2936 2937 2960 2962 2986 2992 3030 3052 3054 3081 3109 3124 3200 3285 3285B 3290 3305 3307 3308 3309 3311 3312 3313 3314 3315 3316 3336 3369 3383 3393 3402 3463 3464 3585 3621 3673 3717 3904 3923 3936 4980 4993 5042 5061 5078 5085 5101 5135 5260 5264 5495 5626 Other 3C 196.1 AM 1316−241 Arp 7 CTQ 327 ESO 510-G13 GAMA202627 GLEAM J0917−0012 Hydra A IC 535 MRC 1138−262 Peekaboo Galaxy PKS 1151−348 RX J0911.4+0551 SDSS J0841+0101 TN J0924−2201 Tololo 1247−232 ZwCl 1693 BCG Galaxy clusters Abell 754 Abell 3411 Abell 3412 Bullet Group Hickson 40 Astronomical events GW170817 Category

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Adapted from the Wikipedia article [Zeta Hydrae](https://en.wikipedia.org/wiki/Zeta_Hydrae) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Zeta_Hydrae?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.