Gamma Geminorum (γ Geminorum, abbreviated Gamma Gem, γ Gem), formally named Alhena , is the third-brightest object in the

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 ...

Gemini Gemini most often refers to: * Gemini (constellation), one of the constellations of the zodiac * Gemini (astrology), an astrological sign Gemini may also refer to: Science and technology Space * Gemini in Chinese astronomy, the Gemini constellat ...

. It has 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 1.9, making it easily visible to the naked eye even in urban regions. Based upon

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

measurements with the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions and distances of ...

satellite, it is located at a distance of roughly .

Properties

Alhena is an

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

star that is exhausting the supply of hydrogen at its core and has entered the

subgiant A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...

stage. The

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 ...

matches 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 A0 IV. Compared to the Sun it has 2.8 times the mass and five times the radius. It is radiating around 200 times the luminosity of the Sun from its outer envelope 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 9,190 K. This gives it a white hue typical of an A-class star. Alhena is a

spectroscopic binary A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

system with a period of 12.6 years (4,614.51 days) in a highly

eccentric Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off- center, in geometry * Eccentricity (graph theory) of a ...

Keplerian orbit In celestial mechanics, a Kepler orbit (or Keplerian orbit, named after the German astronomer Johannes Kepler) is the motion of one body relative to another, as an ellipse, parabola, or hyperbola, which forms a two-dimensional orbital plane in ...

. The secondary, with 1.07 times the mass of the Sun, is likely a

G-type main-sequence 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, main-sequence star (luminosity class V) of stellar classification, spectral type G. Such a star has about 0.9 to ...

Etymology

''γ Geminorum'' ( Latinised to ''Gamma Geminorum'') 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 ''Alhena'' is 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 ...

الهنعة ''Al Han'ah'', 'the brand' (on the neck of the camel), whilst the alternate name ''Almeisan'' is from the Arabic المیسان ''Al Maisan'', 'the shining one.' ''Al Hanʽah'' was the name of star association consisting of this star, along with

Mu Geminorum Mu Geminorum or μ Geminorum, formally named Tejat (), is a single star in the northern constellation of Gemini. From parallax measurements obtained during the Hipparcos mission, it is roughly distant from the Sun. The position of the st ...

(Tejat Posterior),

Nu Geminorum Nu Geminorum, Latinized from ν Geminorum, is a triple star system in the constellation Gemini. It has an apparent visual magnitude of 4.16, which is bright enough to be visible to the naked eye on a dark night. Based upon an annual ...

Eta Geminorum Eta Geminorum (η Geminorum, abbreviated Eta Gem, η Gem), formally named Propus , is a triple star system in the constellation of Gemini. It is a variable star visible to the naked eye, around 380 light years from the Sun. The positi ...

(Tejat Prior) and

Xi Geminorum Xi Geminorum (ξ Geminorum, abbreviated Xi Gem, ξ Gem), formally named Alzirr , is a star in the zodiac constellation of Gemini. It forms one of the four feet of the outline demarcating the Gemini twins. The star has an apparent visual m ...

(Alzirr). They also were associated in ''Al Nuḥātai'', the dual form of ''Al Nuḥāt'', 'a Camel's Hump'. 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 ''Alhena'' for this star. In the catalogue of stars in the ''Calendarium of Al Achsasi Al Mouakket'', this star was designated ''Nir al Henat'', 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 ''Prima του al Henat'', meaning 'the brightest of Al Henat'. 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 ''

Well A well is an excavation or structure created on the earth by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. The ...

(asterism)'', refers to an asterism consisting of γ Geminorum, ε Geminorum,

ζ Geminorum Zeta Geminorum (ζ Geminorum, abbreviated Zeta Gem, ζ Gem) is a bright star with cluster components, distant optical components and a likely spectroscopic partner in the zodiac constellation of Gemini — in its south, on the left 'leg' ...

, λ Geminorum, μ Geminorum, ν Geminorum, ξ Geminorum and 36 Geminorum. Consequently, γ Geminorum itself is known as (, .)香港太空館 – 研究資源 – 亮星中英對照表
, Hong Kong Space Museum. Accessed on line November 23, 2010.

Conjunctions

Gamma Geminorum is 6° south of the

ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

, far enough so that the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

never occults it. Similarly,

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

s in conjunction with this star almost always pass several degrees to the north, but

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

will have a series of close conjunctions with Gamma Geminorum starting in August 2143, and continuing every eight years after over the remainder of that century. The Sun passes Gamma Geminorum on or around June 30 every year.

In culture

''Alhena'' was the name of a

Dutch Dutch or Nederlands commonly refers to: * Something of, from, or related to the Netherlands ** Dutch people as an ethnic group () ** Dutch nationality law, history and regulations of Dutch citizenship () ** Dutch language () * In specific terms, i ...

ship that rescued many people from an Italian cruise liner, the '' SS Principessa Mafalda'', in October 1927. In addition, the American

attack cargo ship Attack may refer to: Warfare and combat * Attack (fencing) * Charge (warfare) * Offensive (military) * Strike (attack) Books and publishing * ''The Attack'' (novel), a book * '' Attack No. 1'', comic and animation * Attack! Books, a publis ...

was named after the star.

References

{{DEFAULTSORT:Gamma Geminorum Geminorum, Gamma Geminorum, 24 Gemini (constellation) A-type subgiants Spectroscopic binaries Alhena 2421 047105 031681 Durchmusterung objects