Alphard (
), designated Alpha Hydrae (α Hydrae, abbreviated Alpha Hya, α Hya), is the brightest
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 constellation of
Hydra. It is a single
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 ...
, cooler than 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 ...
but larger and more luminous. It is about 177
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 away.
Nomenclature
''α Hydrae'' (
Latinised to ''Alpha Hydrae'') is the star'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 ...
.
The traditional name ''Alphard'' is 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 ...
الفرد (''al-fard''), "the individual", there being no other bright stars near it. It was also known as the "backbone of the Serpent" to the
Arabs
Arabs (, , ; , , ) are an ethnic group mainly inhabiting the Arab world in West Asia and North Africa. A significant Arab diaspora is present in various parts of the world.
Arabs have been in the Fertile Crescent for thousands of yea ...
. In the catalogue of stars in the ''Calendarium of Al Achsasi Al Mouakket'', it was designated ''Soheil al Fard'', which was translated into
Latin
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
as ''Soheil Solitarius'', meaning ''the bright solitary one''. In 2016, the
International Astronomical Union
The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...
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's first bulletin of July 2016
included a table of the first two batches of names approved by the WGSN; which included ''Alphard'' for this star. It is now so entered in the IAU Catalog of Star Names.
The Danish astronomer
Tycho Brahe
Tycho Brahe ( ; ; born Tyge Ottesen Brahe, ; 14 December 154624 October 1601), generally called Tycho for short, was a Danish astronomer of the Renaissance, known for his comprehensive and unprecedentedly accurate astronomical observations. He ...
dubbed it ''Cor Hydræ'', Latin for 'the heart of Hydra'.
In
Chinese, (), meaning ''
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 ...
'', refers to an
asterism consisting of Alphard,
τ1 Hydrae,
τ2 Hydrae,
ι Hydrae
Iota Hydrae (ι Hydrae, abbreviated Iota Hya, ι Hya), formally named Ukdah , is a star in the constellation of Hydra, about 8° to the north-northwest of Alphard (Alpha Hydrae) and just to the south of the celestial equator. Visible to ...
,
26 Hydrae
26 Hydrae is a binary star system located 334 light years away from the Sun in the equatorial constellation of Hydra. It is visible to the naked eye as a faint, yellow-hued point of light with a combined apparent visual magnitude of ...
,
27 Hydrae
27 Hydrae is a triple star system system in the equatorial constellation of Hydra, located 222 light years away from the Sun. It is visible to the naked eye as a faint, orange-hued star with a combined apparent visual magnitude of ...
,
HD 82477
HD may refer to:
Business
* H-D or Harley-Davidson, a motorcycle manufacturer
* The Home Depot, NYSE stock symbol: HD
Chemistry
* Hydrogen deuteride, a diatomic compound of hydrogen and deuterium
* Mustard gas
Codes
* Air Do, formerly Ho ...
and
HD 82428
HD may refer to:
Business
* H-D or Harley-Davidson, a motorcycle manufacturer
* The Home Depot, NYSE stock symbol: HD
Chemistry
* Hydrogen deuteride, a diatomic compound of hydrogen and deuterium
* Mustard gas
Codes
* Air Do, formerly Ho ...
. Consequently, Alphard itself is known as (), "the First Star of Star". In
ancient China
The history of China spans several millennia across a wide geographical area. Each region now considered part of the Chinese world has experienced periods of unity, fracture, prosperity, and strife. Chinese civilization first emerged in the Y ...
it formed part of an asterism called the "red bird".
Properties

Alphard has 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 ...
.
Its estimated age is 420 million years
and it has evolved away from the
main sequence
In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
to become a
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
spectral classification
''Spectral'' is a 2016 Hungarian-American military science fiction action film co-written and directed by Nic Mathieu. Written with Ian Fried & George Nolfi, the film stars James Badge Dale as DARPA research scientist Mark Clyne, with Max M ...
of K3 and
luminosity class
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 ...
III.
The angular diameter has been measured using
interferometry
Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important inves ...
, 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 ...
, it yields a value of . Assuming the distance of , it yields a physical size of 57.6 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 ...
.
[
Alphard's ]spectrum
A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...
shows a mild excess of barium
Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.
Th ...
, an element that is normally produced by the s-process
The slow neutron-capture process, or ''s''-process, is a series of nuclear reactions, reactions in nuclear astrophysics that occur in stars, particularly asymptotic giant branch stars. The ''s''-process is responsible for the creation (nucleosynt ...
of nucleosynthesis
Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in ...
. Typically a barium star belongs to a binary system
A binary system is a system of two astronomical bodies of the same kind that are comparable in size. Definitions vary, but typically require the center of mass to be located outside of either object. (See animated examples.)
The most common ki ...
and the anomalies in abundances are explained by mass transfer from a companion white dwarf
A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
star.
Precise radial velocity measurements have shown variations in the stellar radial velocities
The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity on ...
and spectral line
A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission (electromagnetic radiation), emission or absorption (electromagnetic radiation), absorption of light in a narrow frequency ...
profiles. The oscillation
Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...
s are multi-periodic with periods from several hours up to several days. The short-term oscillations were assumed to be a result of stellar pulsations, similar to the solar ones. A correlation between the variations in the asymmetry of the spectral line profile and the radial velocity has also been found. The multi-periodic oscillations make HD 81797 (Alphard) an object of interest for asteroseismologic investigations.
Modern legacy
Alphard appears on the flag of Brazil
The national flag of Brazil is a blue disc depicting a starry sky (which includes the Crux, Southern Cross) spanned by a curved band inscribed with the List of national mottos, national motto ('Order and Progress'), within a yellow rhombus, on ...
, symbolising the state of Mato Grosso do Sul
Mato Grosso do Sul ( ) is one of Federative units of Brazil, Brazil's 27 federal units, located in the southern part of the Central-West Region, Brazil, Central-West Region, bordering five Brazilian states: Mato Grosso (to the north), Goiás and ...
.
The Toyota Alphard
The is a minivan produced by the Japanese automaker Toyota since 2002. It is available as a seven or eight-seater with petrol and hybrid engine options. Hybrid variants have been available since 2003, which incorporates Toyota's Hybrid Syne ...
is a minivan
Minivan (sometimes called simply a van) is a car classification for vehicles designed to transport passengers in the rear seating row(s), with reconfigurable seats in two or three rows . The equivalent classification in Europe is MPV (multi-p ...
named after this star.
The character Roy Alphard from Japanese light novel
A is a type of Genre fiction, popular literature novel from Japan usually classified as young adult fiction, generally targeting Adolescence, teens to Young adult, twenties or older. The definition is very vague, and wide-ranging.
The abbr ...
series '' Re:Zero'' is named after this star.
Notes
References
{{Stars of Hydra
Hydrae, Alpha
Hydra (constellation)
K-type bright giants
K-type giants
Alphard
Hydrae, 30
046390
081797
BD-08 2680
3748