Zeta Hydrae (ζ Hya, ζ Hydrae) is a solitary star in the

equatorial Equatorial may refer to something related to: *Earth's equator **the tropics, the Earth's equatorial region **tropical climate *the Celestial equator ** equatorial orbit **equatorial coordinate system ** equatorial mount, of telescopes * equatorial ...

constellation of Hydra. This is a generally faint constellation, so, at an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of +3.10, this is the third-brightest member after

Alphard Alphard , designated Alpha Hydrae (α Hydrae, abbreviated Alpha Hya, α Hya), is the brightest star in the constellation of Hydra. It is a single giant star, cooler than the Sun but larger and more luminous. It is about 177 light-year ...

and Gamma Hydrae.

Distance

The distance to this star has been measured using the parallax technique, yielding a value of roughly . At this distance, the

visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of the star is diminished by 0.03 as a result of

extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

from intervening gas and dust. Delta Hydrae is about from Zeta Hydrae and may be a largely co-moving object. The star has one of the lower-error margin readings among those of the

Gaia spacecraft ''Gaia'' is a space observatory of the European Space Agency (ESA), launched in 2013 and expected to operate until 2025. The spacecraft is designed for astrometry: measuring the positions, distances and motions of stars with unprecedented preci ...

which computes a parallax of 20.7182 ± 0.3925 mas and, if correct, a distance of 157 ± 3 light years.

Characteristics

With a stellar classification of G9 II-III, this is an

evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

giant star A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...

that is radiating 132 times the

luminosity of the Sun The solar luminosity (), is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal ...

from its outer envelope at an effective temperature of 4,925 K. At this heat, the star glows with the yellow hue of a

G-type star A G-type main-sequence star (Spectral type: G-V), also often, and imprecisely called a yellow dwarf, or G star, is a main-sequence star (luminosity class V) of spectral type G. Such a star has about 0.9 to 1.1 solar masses and an effective temp ...

. The radius of this star, as measured using interferometry, is about 18 times the Sun's radius. It has an estimated 4.2 times the mass of the Sun and is around old.

Name and etymology

This star, along with δ Hya (Lisan al Sudja), ε Hya, η Hya, ρ Hya and σ Hya (Minchir), were Ulug Beg's ''Min al Azʽal'', "Belonging to the Uninhabited Spot". 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). In

Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of ...

, (), meaning ''

Willow Willows, also called sallows and osiers, from the genus ''Salix'', comprise around 400 speciesMabberley, D.J. 1997. The Plant Book, Cambridge University Press #2: Cambridge. of typically deciduous trees and shrubs, found primarily on moist so ...

'', refers to an asterism consisting of ζ Hydrae, δ Hydra, σ Hydrae, η Hydrae, ρ Hydrae, ε Hydrae, ω Hydrae and θ Hydrae Consequently, ζ Hydrae itself is known as (, en, the Sixth Star of Willow).
AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 28 日
/ref> The people of

Groote Eylandt Groote Eylandt ( Anindilyakwa: ''Ayangkidarrba'' meaning "island" ) is the largest island in the Gulf of Carpentaria and the fourth largest island in Australia. It was named by the explorer Abel Tasman in 1644 and is Dutch for "Large Island" i ...

called ''Unwala'', "The Crab", for the star cluster including this star, δ Hya (Lisan al Sudja), ε Hya, η Hya, ρ Hya and σ Hya (Minchir).

References

{{DEFAULTSORT:Zeta Hydrae Hydrae, Zeta Hydra (constellation) Minazal V Hydrae, 16 043813 G-type bright giants 076294 3547 Durchmusterung objects