The [[Bayer designation]] '''Tau Hydrae''' (τ Hya, τ Hydrae) is shared by two [[star system]]s in the equatorial [[constellation]] of [[Hydra (constellation)|Hydra]]. The two stars are separated by 1.74° in the sky.
* [[Tau1 Hydrae|τ<sup>1</sup> Hydrae]], [[triple star system]] * [[Tau2 Hydrae|τ<sup>2</sup> Hydrae]], [[astrometric binary]]
The stars τ<sup>1</sup> Hya and τ<sup>2</sup> Hya, along with [[Iota Hydrae|ι Hya]] and the 5th‑magnitude [[33 Hydrae|33 Hya]] (A Hydrae), were Ptolemy's Καμπή (Kampē); but Kazwini knew them as ʽUḳdah, the Knot.<ref>{{cite book | last=Allen | first=R. H. | year=1963 | authorlink=Richard Hinckley Allen | title=Star Names: Their Lore and Meaning | url=https://archive.org/details/starnamestheirlo00alle/page/250 | accessdate=2010-12-12 | edition=Reprint | publisher=Dover Publications Inc | location=New York, NY | isbn=0-486-21079-0 | page=[https://archive.org/details/starnamestheirlo00alle/page/250 250] | url-access=registration }}</ref> According to the catalogue of stars in the ''Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars'', ''Uḳdah'' was the title for four stars: τ<sup>1</sup> Hya as ''Uḳdah I'', τ<sup>2</sup> Hya as ''Uḳdah II'', 33 Hya as ''Uḳdah III'' and [[Iota Hydrae|ι Hya]] as ''Uḳdah IV''.<ref>[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720005197_1972005197.pdf 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]</ref> The name Ukdah is now officially applied to ι Hydrae.
In [[Chinese language|Chinese]], {{lang|zh|柳宿}} ({{lang|zh-Latn|Xīng Sù}}), meaning ''[[Star (Chinese constellation)|Star]] (asterism)'', refers to an asterism consisting of τ<sup>1</sup> and τ<sup>2</sup> Hydrae, [[Alphard]], [[Iota Hydrae|ι Hydrae]], [[26 Hydrae]], [[27 Hydrae]], [[HD 82477]] and [[HD 82428]].<ref>{{in lang|zh}} ''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}}.</ref> Consequently, τ<sup>1</sup> and τ<sup>2</sup> Hydrae are known as {{lang|zh|星宿二}} ({{lang|zh-Latn|Xīng Sù èr}}, {{langx|en|the Second Star of Star}}) and {{lang|zh|星宿三}} ({{lang|zh-Latn|Xīng Sù sān}}, {{langx|en|the Third Star of Star}}) respectively.<ref>{{in lang|zh}} [http://aeea.nmns.edu.tw/2006/0605/ap060529.html AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 29 日] {{Webarchive|url=https://web.archive.org/web/20110522120541/http://aeea.nmns.edu.tw/2006/0605/ap060529.html |date=2011-05-22 }}</ref>
== References == {{reflist}}
{{Stars of Hydra|state=collapsed}}
{{SIA |astronomical objects}}
[[Category:Bayer objects|Hydrae, Tau]] [[Category:Hydra (constellation)]]