The Bayer designation Tau Hydrae (τ Hya, τ Hydrae) is shared by two star systems in the equatorial constellation of Hydra. The two stars are separated by 1.74° in the sky.
τ1 Hydrae, triple star system τ2 Hydrae, astrometric binary
The stars τ1 Hya and τ2 Hya, along with ι Hya and the 5th‑magnitude 33 Hya (A Hydrae), were Ptolemy's Καμπή (Kampē); but Kazwini knew them as ʽUḳdah, the Knot. 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: τ1 Hya as Uḳdah I, τ2 Hya as Uḳdah II, 33 Hya as Uḳdah III and ι Hya as Uḳdah IV.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 The name Ukdah is now officially applied to ι Hydrae.
In Chinese, (), meaning Star (asterism), refers to an asterism consisting of τ1 and τ2 Hydrae, Alphard, ι Hydrae, 26 Hydrae, 27 Hydrae, HD 82477 and HD 82428. 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, . Consequently, τ1 and τ2 Hydrae are known as (, ) and (, ) respectively. AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 29 日
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