Alpha Persei (
Latinized from α Persei, abbreviated Alpha Per, α Per), formally named Mirfak
(pronounced or ), 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
northern 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
Perseus
In Greek mythology, Perseus (, ; Greek language, Greek: Περσεύς, Romanization of Greek, translit. Perseús) is the legendary founder of the Perseid dynasty. He was, alongside Cadmus and Bellerophon, the greatest Greek hero and slayer of ...
, outshining the constellation's best-known star,
Algol (β Persei). Alpha Persei 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 1.8,
[ and is a ]circumpolar star
A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets below the horizon due to its apparent proximity to one of the celestial poles. Circumpolar stars are therefore visible from said location toward the nearest p ...
when viewed from mid-northern latitudes.
Alpha Persei lies in the midst of a cluster of stars named as the eponymous Alpha Persei Cluster
The Alpha Persei Cluster, also known as Melotte 20 or Collinder 39, is an open cluster of stars in the northern constellation of Perseus (constellation), Perseus. To the naked eye, the cluster consists of several blue-hued spectral type B stars. ...
, or ''Melotte 20'', which is easily visible in binoculars
Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...
and includes many of the fainter stars in the constellation.[ Determined distance using the trigonometric ]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 ...
, places the star away.[
]
Nomenclature
''α Persei'' 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 star also bore the traditional names Mirfak and Algenib, which are 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 ...
in origin. The former, meaning 'Elbow' and also written Mirphak, Marfak or Mirzac, comes from the Arabic ''Mirfaq al-Thurayya'', while Algenib, also spelt Algeneb, Elgenab, Gęnib, Chenib or Alchemb, is derived from الجنب ''al-janb'', or الجانب ''al-jānib'', 'the flank' or 'side'. and was also the traditional name for Gamma Pegasi
Gamma Pegasi is a binary star in the constellation of Pegasus
Pegasus (; ) is a winged horse in Greek mythology, usually depicted as a white stallion. He was sired by Poseidon, in his role as horse-god, and foaled by the Gorgon Med ...
. 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 ''Mirfak'' for this star (Gamma Pegasi was given the name ''Algenib'').
''Hinaliʻi'' is the name of the star in Native Hawaiian
Native Hawaiians (also known as Indigenous Hawaiians, Kānaka Maoli, Aboriginal Hawaiians, or simply Hawaiians; , , , and ) are the Indigenous peoples of Oceania, Indigenous Polynesians, Polynesian people of the Hawaiian Islands.
Hawaiʻi was set ...
astronomy. The name of the star is meant to commemorate a great tsunami
A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...
and mark the beginning of the migration of Maui. According to some Hawaiian folklore
Folklore in Hawaii in modern times is a mixture of various aspects of Hawaiian mythology and various urban legends that have been passed on regarding various places in the Hawaiian islands. The following is a partial list of some of these legend ...
, Hinaliʻi is the point of separation between the Earth and the sky that happened during the creation of the Milky Way
The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
.
Assemani alluded to a title on the Borgian globe, ''Mughammid'' (مغمد), or ''Muliammir al Thurayya'' (ملىمرٱلطرى), the Concealer of the Pleiades
The Pleiades (), also known as Seven Sisters and Messier 45 (M45), is an Asterism (astronomy), asterism of an open cluster, open star cluster containing young Stellar classification#Class B, B-type stars in the northwest of the constellation Tau ...
, which, from its location, may be for this star.
This star, together with γ Persei
Gamma Persei (Gamma Per, γ Persei, γ Per) is a binary star system in the constellation Perseus (constellation), Perseus. The combined apparent visual magnitude of the pair is +2.9, making it the fourth-brightest member of ...
, δ Persei
Delta Persei (Delta Per, δ Persei, δ Per) is a double star in the northern constellation of Perseus. It has an apparent visual magnitude of 3.01, making it readily visible with the naked eye. Parallax measurements give i ...
, η Persei
Eta Persei (η Persei, abbreviated Eta Per, η Per), is a red supergiant in the constellation of Perseus. Parallax measurements by the Gaia spacecraft imply that it is 1,000 is light-years away from Earth. At such distance, interstellar ...
, σ Persei
Sigma Persei (Sigma Per, σ Persei, σ Per) is an orange stellar classification, K-type giant star, giant star with an apparent magnitude of +4.36. It is approximately 343 light-years from Earth.
Sigma Persei is mov ...
and ψ Persei
Psi Persei (Psi Per, ψ Persei, ψ Per) is a single Be star in the northern constellation of Perseus. It has an apparent visual magnitude of about 4.2, so it is visible to the naked eye at night under suitably dark skies ...
, has been called ''the Segment of Perseus''.
In Chinese, (), meaning '' Celestial Boat'', refers to an asterism consisting of α Persei, γ Persei, δ Persei, η Persei, μ Persei, ψ Persei
Psi Persei (Psi Per, ψ Persei, ψ Per) is a single Be star in the northern constellation of Perseus. It has an apparent visual magnitude of about 4.2, so it is visible to the naked eye at night under suitably dark skies ...
, 48 Persei
48 Persei (also known as c Persei, 48 Per, HR 1273, HIP 19343, or ) is a Be star in the constellation Perseus, approximately the 500th brightest of the visible stars in apparent magnitude. It is "well known for its complex spectrum and ...
and HD 27084
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 H ...
. Consequently, the Chinese name
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-ethni ...
for α Persei itself is (, ).[AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 11 日]
Physical properties
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 ...
of Alpha Persei 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 F5 Ib,[ revealing it to be a ]supergiant
Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute visual magnitudes between about −3 and −8. The temperatures of supergiant stars range ...
star in the latter stages of its evolution
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 ...
. It has a similar spectrum to Procyon
Procyon () is the brightest star in the constellation of Canis Minor and usually the list of brightest stars, eighth-brightest star in the night sky, with an apparent visual magnitude of 0.34. It has the Bayer designation α Canis Min ...
A, though the latter star is much less luminous. This difference is highlighted in their spectral designation under the Yerkes spectral classification, published in 1943, where stars are ranked on luminosity as well as spectral typing. Procyon A is thus F5 IV,[ a ]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 ...
star. Since 1943, the spectrum of Alpha Persei has served as one of the stable anchor points by which other stars are classified.[
Alpha Persei has about 7.3 times the ]Sun's mass
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 has expanded to roughly 53 times the size of the Sun.] It is radiating 4,020 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 s ...
from its photosphere
The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...
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 ,[ which creates the yellow-white glow of an ]F-type star
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
.[
In the ]Hertzsprung–Russell diagram
The Hertzsprung–Russell diagram (abbreviated as H–R diagram, HR diagram or HRD) is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities and their stellar classifications or effective temp ...
, Alpha Persei lies inside the region in which Cepheid variable
A Cepheid variable () is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period (typically 1–100 days) and amplitude. Cepheids are important cosmi ...
s are found.[ It is thus useful in the study of these stars, which are important ]standard candle
The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible ...
s.[ Despite Mirfak being not a Cepheid, ]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 ...
photometry show a 0.006-magnitude
Magnitude may refer to:
Mathematics
*Euclidean vector, a quantity defined by both its magnitude and its direction
*Magnitude (mathematics), the relative size of an object
*Norm (mathematics), a term for the size or length of a vector
*Order of ...
variation with a period of 9.5 days.[
]
Search for planets
Alpha Persei has periodic radial velocity
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 ...
variations, with an amplitude of 70.8 ± 1.6 m/s. These variations are of uncertain origin; a 2012 study considered the possibility of them being caused by an orbiting exoplanet
An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...
, estimated to have a minimum mass of approximately 6.6 times that of Jupiter and an orbital period of 128 days, but the claimed period may not be stable over 20 years so the exoplanet was considered doubtful. The authors suggested rotational modulation due to surface activity such as starspots as a more likely explanation of the radial velocity variations. In previous publications, periodic radial velocity variations of 87.7 or 77.7 days have been reported, but these have not been confirmed.[
A further study, published in 2025, analysing radial velocity observations, found that the period of ~130 days weakened and disappeared during a time, while a 66-day period appeared. The hypothesis of a planet around Mirfak can now be discarded, considering the period changes over time. Variations with periods of 9.8 and 77.7 days, reported in previous studies, have not been detected. The most reasonable explanation to the radial velocity variations is stellar oscillations.][
]
References
{{Portal bar, Astronomy, Stars, Outer space
F-type supergiants
Perseus (constellation)
Alpha Persei Cluster
Persei, Alpha
BD+49 0917
Persei, 33
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015863
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Mirfak