Mirach is a prominent

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 Andromeda. It is pronounced and has the

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 ...

Beta Andromedae, which is Latinized from β Andromedae. This star is positioned northeast of the ''Great Square'' 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 Medusa. Pegasus was the brother of Chrysaor, both born from Medusa's blood w ...

and is potentially visible to all observers north of

latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

54° S. It is commonly used by stargazers to find the

Andromeda Galaxy The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a Galaxy#Isophotal diameter, D25 isop ...

. The

galaxy A galaxy is a Physical system, system of stars, stellar remnants, interstellar medium, interstellar gas, cosmic dust, dust, and dark matter bound together by gravity. The word is derived from the Ancient Greek, Greek ' (), literally 'milky', ...

NGC 404, also known as Mirach's Ghost, is seven

arcminutes A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

away from Mirach. This star 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 around 2.07, varying between 2.01 and 2.10, which at times makes it the brightest star in the constellation. 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, it is roughly from the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

. Its apparent magnitude is reduced by 0.06 by

extinction Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

due to gas and dust along the line of sight. The star has a negligible

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 ...

of 0.1 km/s, but with a relatively large

proper motion Proper motion is the astrometric measure of changes in the apparent places of stars or other celestial objects as they move relative to the center of mass of the Solar System. It is measured relative to the distant stars or a stable referenc ...

, traversing the

celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...

at an

angular rate In physics, angular frequency (symbol ''ω''), also called angular speed and angular rate, is a scalar measure of the angle rate (the angle per unit time) or the temporal rate of change of the phase argument of a sinusoidal waveform or sine f ...

of ·yr⁻¹.

Properties

Mirach is a single, aging

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...

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 M0 III. It is currently on the

asymptotic giant branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

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 ...

. The star has an estimated 2.49 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 ...

. Having exhausted the supply of hydrogen at its

core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (laboratory), a highly specialized shared research resource * Core (manufacturing), used in casting and molding * Core (optical fiber ...

, the outer envelope of the star has expanded to around 86 times the size of the Sun. It is radiating 1,675 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 ...

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 . Mirach is suspected of being a semiregular

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

, with an

varies from +2.01 to +2.10. Since 1943 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 this star has been one of the stable anchor points by which other stars are classified.

Nomenclature

''Beta Andromedae'' is the star's

. It had the traditional name of ''Mirach'', and its variations, such as ''Mirac'', ''Mirar'', ''Mirath'', ''Mirak'', etc. (the name is spelled ''Merach'' in Burritt's ''The Geography of the Heavens''), which come from the star's description in the '' Alfonsine Tables'' of 1521 as ''super mizar''. Here, ''mirat'' is a corruption of 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 ...

مئزر '' mīzar'' "girdle", which appeared in a

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 ...

translation of the ''

Almagest The ''Almagest'' ( ) is a 2nd-century Greek mathematics, mathematical and Greek astronomy, astronomical treatise on the apparent motions of the stars and planetary paths, written by Ptolemy, Claudius Ptolemy ( ) in Koine Greek. One of the most i ...

''. This word refers to Mirach's position at the left hip of the princess Andromeda. 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 ''Mirach'' for this star. Mirach is listed in the Babylonian MUL.APIN as KA.MUSH.I.KU.E, meaning "the Deleter" (the alternative star is α Cas). Medieval astronomers writing in Arabic called Mirach ''Janb al-Musalsalah'' (); it was part of the 28th ''manzil'' (Arabian

lunar mansion Often called lunar mansion, a lunar station or lunar house is a segment of the ecliptic through which the Moon passes in orbit of the Moon, its orbit around the Earth. The concept was used by several ancient cultures as part of their calendrical ...

) ''Baṭn al-Ḥūt'', the Belly of the Fish, or ''Qalb al-Ḥūt'', the Heart of the Fish. The star has also been called ''Cingulum'' and ''Ventrale''. This ''al-Ḥūt'' was an indigenous Arabic constellation, not the Western "Northern Fish" part of the constellation Pisces. These names are not from the Arabic ''marāqq'', loins, because it was never called ''al-Marāqq'' in Arabian astronomy. ''Al Rishā, the Cord (of the well-bucket), on al-Sūfī's star map. It is the origin of the proper name Alrescha for Alpha Piscium. In Chinese, (), meaning '' Legs'', refers to an asterism consisting of Mirach (β Andromedae), η Andromedae, 65 Piscium, ζ Andromedae, ε Andromedae, δ Andromedae, π Andromedae, ν Andromedae,

μ Andromedae Mu Andromedae is a binary star system in the northern constellation of Andromeda (constellation), Andromeda. Its Bayer designation is Romanization of Greek, Latinized from μ Andromedae, and abbreviated Mu And or μ And, r ...

, σ Piscium, τ Piscium, 91 Piscium, υ Piscium, φ Piscium, χ Piscium and ψ¹ Piscium. 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 β Andromedae itself is (, ). Mirach was considered the standard "black" star; ''black'' could mean "dark red" in this context, especially in comparison to

Antares Antares is the brightest star in the constellation of Scorpius. It has the Bayer designation α Scorpii, which is Latinisation of names, Latinised to Alpha Scorpii. Often referred to as "the heart of the scorpion", Antares is flanked by ...

, the standard red star. The people of

Micronesia Micronesia (, ) is a subregion of Oceania, consisting of approximately 2,000 small islands in the Northwestern Pacific Ocean. It has a close shared cultural history with three other island regions: Maritime Southeast Asia to the west, Poly ...

named this star ''Kyyw'', meaning "The Porpoise", and this was used as one of the names of the months in Micronesia.

Substellar companion

A 2023 study detected

variations in Mirach (HD 6860), showing evidence of a substellar companion, likely a

brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...

References

External links

*
Image MIRACH
* {{Stars of Andromeda M-type giants Asymptotic-giant-branch stars Semiregular variable stars Andromeda (constellation) Andromedae, Beta BD+34 0198 Andromedae, 43 0053.3 006860 005447 0337 Mirach Brown dwarfs

Properties

Nomenclature

Substellar companion

References

Further reading

External links