Tau1 Hydrae
multiple star system in the constellation Hydra
Tau1 Hydrae is a triple star system in the equatorial constellation of Hydra. Based upon the annual parallax shift of the two visible components as seen from Earth, they are located about 18 parsecs (59 ly) from the Sun. The system has a combined apparent visual magnitude of +4.59, which is bright enough to be visible to the naked eye at night.
The inner pair of stars form a single-lined spectroscopic binary with an orbital period of about 2,807 days and an eccentricity of 0.33. The visible member of the pair, component A, is a visual magnitude 4.60 F-type main sequence star with a stellar classification of F6 V. During the 1990s, it was thought to be a Gamma Doradus variable, but this was later discounted as it shows no short-term photometric variability. The star does show some long-term variability, possibly as a result of a magnetic activity cycle similar to the solar cycle.
The tertiary member, component B, is a visual magnitude 7.15 K-type star with a class of K0. It lies at a separation of 1,120 AU from the primary. As of 2012, it was positioned at an angular separation of 67.5 arc seconds along a position angle of 4°.
This star along with τ2 Hydrae, ι Hydrae and 33 Hydrae (A Hydrae) were traditionally known as Ukdah, Arabic for "knot".
“Tau1 Hydrae” enters the record as multiple star system in the constellation Hydra. Crown Archives preserves that source wording while asking what Tau1, Hydrae and multiple can confirm, complicate or overturn.
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The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Sep 13, 2026. The linked authority identifier is Q3232684. None of the 0 selected statements returned an explicit reference. The first chronological checks are 2012.
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This entry incorporates text from “Tau1 Hydrae” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.