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{{Short description|Star in the constrellation Hydrus}}{{Starbox begin}}{{Starbox image| image = }}{{Starbox observe }} }}}}{hide}Starbox reference {edih}Alpha Hydri, Latinized from α Hydri, is the second brightest star in the southern circumpolar constellation of Hydrus. It is readily visible to the naked eye with an apparent visual magnitude of +2.9. It is sometimes informally known as the Head of Hydrus. This should not be confused with Alpha Hydrae (Alphard) in the constellation Hydra. Alpha Hydri is one of only three stars in the constellation Hydrus that are above the fourth visual magnitude. This star can be readily located as it lies to the south and east of the prominent star Achernar in the constellation Eridanus.Based upon parallax measurements from the Hipparcos mission, Alpha Hydri is located at a distance of about {{Convert|71.8|ly|pc|abbr=off|lk=on}} from Earth. This subgiant star is three times larger and twice as massive as the Sun, with a stellar classification of F0 IV. It is about 810 million years old and is radiating 21 times the Sun’s luminosity from its outer atmosphere at an effective temperature of 7,087 K. Alpha Hydri emits X-rays similar to Altair. The space velocity components of this star are [U, V, W] = {{nowrap|[−14, −14, -2] km/s}}.BOOK

Naming

In Chinese caused by adaptation of the European southern hemisphere constellations into the Chinese system, (), meaning Snake’s Head, refers to an asterism consisting of α Hydri and β Reticuli. Consequently, α Hydri itself is known as (, .){{in lang|zh}} AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 å¹´ 7 月 27 æ—¥

References

{{reflist|refs=JOURNAL JOURNAL, F., van Leeuwen, November 2007, Validation of the new Hipparcos reduction, Astronomy and Astrophysics, 474, 2, 653–664, 2007A&A...474..653V, 10.1051/0004-6361:20078357, 0708.1752, 18759600, JOURNAL, Gutierrez-Moreno, Adelina, A System of photometric standards, Publications of the Department of Astronomy University of Chile, Publicaciones Universidad de Chile, Department de Astronomy, 1, 1–17, 1966, 1966PDAUC...1....1G, etal, JOURNAL, Wilson, R. E., 1953, General Catalogue of Stellar Radial Velocities, Carnegie Institute Washington D.C. Publication, Carnegie Institute of Washington D.C., 1953GCRV..C......0W, {{citation | last1=Malagnini | first1=M. L. | last2=Morossi | first2=C. | title=Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars | journal=Astronomy and Astrophysics Supplement Series | volume=85 | issue=3 | pages=1015–1019 |date=November 1990 | bibcode=1990A&AS...85.1015M }}WEB, LTT 1059, SIMBAD, Centre de Données astronomiques de Strasbourg,simbad.u-strasbg.fr/simbad/sim-basic?Ident=LTT+1059, 2009-10-13, JOURNAL, Lachaume, R., Age determinations of main-sequence stars: combining different methods, Astronomy and Astrophysics, 348, 897–909, August 1999, 1999A&A...348..897L,adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999A%26A...348..897L&link_type=ARTICLE&db_key=AST&high=, 2009-10-13, etal, BOOK, Patrick, Moore, 2005, The observer’s year: 366 nights of the universe,archive.org/details/observersyearnig00moor, limited, 4, 2nd, Springer, 1-85233-884-9, BOOK, Richard Hinckley, Allen, 1963, 377, Star Names, Their Lore and Meaning, Dover, New York, 0-486-21079-0, registration,archive.org/details/starnamestheirlo00alle/page/377, }}{{Stars of Hydrus}}