Sigma Hydrae (σ Hydrae, abbreviated Sigma Hya, σ Hya), also named Minchir , is a solitary

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

in the equatorial

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

of Hydra. It is visible to the naked eye with an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of 4.48. The estimated distance to this star from the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

, based upon an annual parallax shift of 8.75 mas, is around 370

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s. At that distance, the visual magnitude of the star is diminished by an interstellar extinction factor of 0.16, due to intervening dust.

Nomenclature

''σ Hydrae'' ( Latinised to ''Sigma Hydrae'') is the system's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

. It bore the traditional name ''Minchir'', appearing as ''Minchir es-schudscha'' in Bode's large

star atlas Celestial cartography, uranography, astrography or star cartography is the aspect of astronomy and branch of cartography concerned with mapping stars, galaxies, and other astronomical objects on the celestial sphere. Measuring the position ...

, ''Uranographia''. The name which derived from the

Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...

appelationمنخر الشجاع ''minkhar ash-shujāʽ'' "the nostril brave one" (the hydra) for this star. The name is erroneously spelt as ''Al Minliar al Shuja'' in the

Yale Yale University is a private Ivy League research university in New Haven, Connecticut, United States. Founded in 1701, Yale is the third-oldest institution of higher education in the United States, and one of the nine colonial colleges ch ...

Bright Star Catalogue The Bright Star Catalogue, also known as the Yale Catalogue of Bright Stars, Yale Bright Star Catalogue, or just YBS, is a star catalogue that lists all stars of stellar magnitude 6.5 or brighter, which is roughly every star visible to the na ...

''. In 2016, the IAU organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(WGSN) to catalog and standardize proper names for stars. The WGSN approved the name ''Minchir'' for this star on 5 September 2017 and it is now so included in the List of IAU-approved Star Names. This star, along with

Delta Hydrae Delta Hydrae, Latinized from δ Hydrae, is a triple star in the equatorial constellation of Hydra. It is visible to the naked eye with an apparent visual magnitude of 4.146. Based upon an annual parallax shift of 20.34 mas, it ...

(Lisan al Shudja),

Epsilon Hydrae Epsilon Hydrae (ε Hydrae, abbreviated Epsilon Hya, ε Hya) is a multiple star system of a combined third magnitude in the constellation of Hydra. Based upon parallax measurements obtained during the Hipparcos mission, it is located ro ...

Zeta Hydrae Zeta Hydrae (ζ Hya, ζ Hydrae) is a solitary star in the equatorial constellation of Hydra. This is a generally faint constellation, so, at an apparent visual magnitude of +3.10, this is the third-brightest member after Alphard and Ga ...

Eta Hydrae Eta Hydrae (η Hydrae) is a star in the equatorial constellation of Hydra (constellation), Hydra. With an apparent visual magnitude of 4.3, it is visible to the naked eye. However, it is the faintest of the five stars that form the "head" ...

and

Rho Hydrae Rho Hydrae, equally written ρ Hydrae, is a binary star in the equatorial constellation of Hydra. It is visible to the naked eye with an apparent visual magnitude of 4.34. The distance to this system, based upon an annual parallax shift ...

, were Ulug Beg's ''Min al Azʽal'', "Belonging to the Uninhabited Spot". (According to a 1971

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

memorandum, ''Min al Azʽal'' or ''Minazal'' were the title for five stars : Delta Hydrae as ''Minazal I'', Eta Hydrae as ''Minazal II'', Epsilon Hydrae as ''Minazal III'', Rho Hydrae as ''Minazal IV'' and Zeta Hydrae as ''Minazal V''.) In

Chinese Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethnic ...

, (), meaning ''

Willow Willows, also called sallows and osiers, of the genus ''Salix'', comprise around 350 species (plus numerous hybrids) of typically deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions. Most species are known ...

(asterism)'', refers to an asterism consisting of Sigma Hydrae, Delta Hydrae, Eta Hydrae, Rho Hydrae, Epsilon Hydrae, Zeta Hydrae, Omega Hydrae and

Theta Hydrae Theta Hydrae, Latinized from θ Hydrae, is a binary star system in the constellation Hydra. It is visible to the naked eye with an apparent visual magnitude of 3.9. The star system has a high proper motion with an annual parallax shift o ...

. Consequently, Sigma Hydrae itself is known as (, ).
AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 28 日
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" ...

, used the name ''Unwala'' ("The Crab") for the star cluster including this star, Delta Hydrae (Lisan al Shudja), Epsilon Hydrae, Zeta Hydrae, Eta Hydrae and Rho Hydrae.

Properties

This is an

evolved Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

K-type

giant star A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsp ...

with a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

of K2 III. The measured

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular separation (in units of angle) describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the ''visual an ...

of this star, after correction for

limb darkening Limb darkening is an optical effect seen in stars (including the Sun) and planets, where the central part of the disk appears brighter than the edge, or '' limb''. Its understanding offered early solar astronomers an opportunity to construct mode ...

, is . At its estimated distance, this yields a physical size of about 27.6 times the

radius of the Sun Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: 1\,R_ = 6.957\ti ...

. It has about three times the

mass of the Sun The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies a ...

and radiates 295 times the

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

from its outer atmosphere at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 4,491 K. Sigma Hydrae is around 430 million years old.

References

{{DEFAULTSORT:Sigma Hydrae K-type giants Hydrae, Sigma Hydra (constellation) Minchir Durchmusterung objects Hydrae, 05 073471 042402 3418