Zeta Andromedae, also named Shimu, is a

binary star 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 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 ...

Andromeda. It is visible to the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...

with 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 ...

that varies from over the course of its 17.7 day orbit. Based on

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 located at a distance of approximately 181

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 from 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 ...

. The system is drifting closer with a heliocentric

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 −24.4 km/s.

Naming

The star's location is in the northern constellation Andromeda, in which it is the second-most southerly of the stars in this often drawn characteristic shape representing the mythical princess asterism, after

η Andromedae Eta Andromedae, also named Kui, is a spectroscopic binary star system in the northern constellation of Andromeda. It consists of two G-type evolved stars orbiting each other with a period of 115.7 days and has an overall apparent ...

. Zeta Andromedae (Zeta And, ζ Andromedae, ζ And) 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 ...

. It also has the

Flamsteed designation A Flamsteed designation is a combination of a number and constellation name that uniquely identifies most naked eye stars in the 88 modern constellations, modern constellations visible from southern England. They are named after John Flamsteed, au ...

34 Andromedae and multiple other designations in stellar catalogues. 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 ''

Legs A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element cap ...

(asterism)'', refers to an asterism consisting of ζ Andromedae,

65 Piscium This is the list of notable stars 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, mythologi ...

ε Andromedae Epsilon Andromedae is a star in the constellation of Andromeda. Its identifier is a Bayer designation that is Latinized from ε Andromedae, and abbreviated eps And or ε And, respectively. This star can be seen with ...

δ Andromedae Delta Andromedae is a triple star system in the northern constellation of Andromeda (constellation), Andromeda. Its identifier is a Bayer designation that is Romanization of Greek, Latinized from δ Andromedae, and abbreviated Delta ...

π Andromedae Pi Andromedae is a binary star system in the northern constellation of Andromeda. Its Bayer designation is latinized from π Andromedae, and abbreviated Pi And or π And, respectively. With an apparent visual magnitude o ...

ν Andromedae Nu Andromedae is a binary star system in the constellation Andromeda. Its Bayer designation is Latinized from ν Andromedae, and abbreviated Nu And or ν And, respectively. The system has an apparent visual magnitude of ...

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 ...

β Andromedae Mirach is a prominent star in the northern constellation of Andromeda. It is pronounced and has the Bayer designation Beta Andromedae, which is Latinized from β Andromedae. This star is positioned northeast of the ''Great Square'' o ...

σ Piscium Sigma Piscium (Sigma Psc, σ Piscium, σ Psc) is a binary star in the zodiac constellation of Pisces. It has an apparent magnitude of +5.50, meaning it is barely visible to the naked eye, according to the Bortle scale ...

τ Piscium Tau Piscium (τ Piscium) is an orange-hued star in the zodiac constellation of Pisces. With an apparent visual magnitude of +4.52, it is a dim star but visible to the naked eye. Based upon an annual parallax shift of 19.32 ...

91 Piscium This is the list of notable stars in the constellation Pisces, sorted by decreasing brightness. See also *List of stars by constellation References * * * * * {{Stars of Pisces *List Pisces Pisces may refer to: *Pisces (astrology), an as ...

υ Piscium Upsilon Piscium is a solitary, white-hued star in the zodiac constellation of Pisces. It is faintly visible to the naked eye, having an apparent visual magnitude of +4.75. Based upon an annual parallax shift of as seen from Earth, it is ...

φ Piscium Phi Piscium, Latinized from φ Piscium, is a quadruple star system approximately 380 light years away in the constellation Pisces. It consists of Phi Piscium A, with a spectral type of K0III, and Phi Piscium B. Phi Piscium A posse ...

χ Piscium Chi Piscium (χ Piscium) is a solitary, orange-hued star in the zodiac constellation of Pisces. It can be seen with the naked eye, having an apparent visual magnitude of +4.64. Based upon an annual parallax shift of 8.50 mas as ...

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 ζ Andromedae itself is (, ). An older Chinese name is ''Tian Shi Mu'', The Eye of the Celestial Pig. Based on this, the

IAU 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 ...

approved the name Shimu for this star on 16 March 2025 and it is now so entered in the IAU Catalog of Star Names.

System

The system 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 ...

whose is classified as an orange K-type

giant In folklore, giants (from Ancient Greek: ''wiktionary:gigas, gigas'', cognate wiktionary:giga-, giga-) are beings of humanoid appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''gia ...

with a mean

apparent magnitude Apparent magnitude () is a measure of the Irradiance, 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 (astronomy), ...

of +4.08. Due to brightness changes caused by the

ellipsoid An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a Surface (mathemat ...

al shape of that object, the system is also an RS Canum Venaticorum-type

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 ...

. It is a magnetically active star with a brightness that varies from magnitude +3.92 to +4.14 over a period of 17.77 days, and its spectrum shows strong and variable Ca II H and K lines. The orbital period of the binary is 17.77 days. The primary component of this binary system, ''Zeta Andromedae Aa'', is one of the few stars who has been resolved using

Doppler imaging Inhomogeneous structures on stellar surfaces, i.e. temperature differences, chemical composition or magnetic fields, create characteristic distortions in the spectral lines due to the Doppler effect. These distortions will move across spectral lin ...

and long-baseline infrared

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 ...

. With resolved images astronomers can recover additional information about this star. Resolved images also allowed observation of

starspot Starspots are stellar phenomena, so-named by analogy with sunspots. Spots as small as sunspots have not been detected on other stars, as they would cause undetectably small fluctuations in brightness. The commonly observed starspots are in gene ...

s (the analogue to

sunspot Sunspots are temporary spots on the Sun's surface that are darker than the surrounding area. They are one of the most recognizable Solar phenomena and despite the fact that they are mostly visible in the solar photosphere they usually aff ...

s), on this star, and their asymmetric distribution showed that the magnetic field of the star is generated by a mechanism different from the

solar dynamo The solar dynamo is a physical process that generates the Sun's magnetic field. It is explained with a variant of the dynamo theory. A naturally occurring electric generator in the Sun's interior produces electric currents and a magnetic field, ...

. A

-like

differential rotation Differential rotation is seen when different parts of a rotating object move with different angular velocities (or rates of rotation) at different latitudes and/or depths of the body and/or in time. This indicates that the object is not rigi ...

of the star was observed instead.

Visual companions

The WDS notes three

visual companion In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a ...

s to the eclipsing binary (Aa and Ab, forming binary A). The parallax of the D star has been measured by ''Gaia'' proving its distance to be much greater than Zeta Andromedae, probably a distant red giant. The closest companion, B, is likewise a background object. The companion C at shares a

common proper motion This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of astronomical object, celestial objects and phenomena ...

and a similar parallax.

Notes

References

External links

Zeta Andromedae
at Alcyone Software's Star Data Pages
Image ζ Andromedae
* Rachael Roettenbacher
"How the face of a distant star reveals our place in the cosmos
" Aeon Magazine etrieved July 27, 2016 {{DEFAULTSORT:Zeta Andromedae K-type giants K-type main-sequence stars Spectroscopic binaries RS Canum Venaticorum variables Rotating ellipsoidal variables 5 Andromeda (constellation) Andromedae, Zeta 0215 BD+23 0106 Andromedae, 34 004502 003693 Shimu