Hubbry Logo
MirachMirachMain
Open search
Mirach
Community hub
Mirach
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Mirach
Mirach
Mirach
View on Wikipedia
from Wikipedia
Mirach
Location of Mirach (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Andromeda
Right ascension 01h 09m 43.91s[1]
Declination +35° 37′ 13.8″[1]
Apparent magnitude (V) 2.067[1] (2.01 to 2.10)[2]
Characteristics
Evolutionary stage Asymptotic giant branch[3]
Spectral type M0 III[4][5]
U−B color index +1.96[6]
B−V color index +1.57[6]
V−R color index 0.9[7]
R−I color index +1.00[8]
Variable type Semiregular[2]
Astrometry
Radial velocity (Rv)0.06±0.13[9] km/s
Proper motion (μ) RA: 175.90[10] mas/yr
Dec.: −112.20[10] mas/yr
Parallax (π)16.52±0.56 mas[10]
Distance197 ± 7 ly
(61 ± 2 pc)
Absolute magnitude (MV)−1.76[11]
Details
Mass2.49[12] M☉
Radius86.4[13] R☉
Luminosity1,675[13] L☉
Surface gravity (log g)0.91±0.10[14] cgs
Temperature3,762±40[14] K
Metallicity [Fe/H]−0.46±0.03[14] dex
Rotation<7900 d (<21.6 years)[5]
Rotational velocity (v sin i)6[5] km/s
Other designations
Mirach, Merach, Mirac, Mizar, β And, Beta Andromedae, Beta And, 43 Andromedae, 43 And, BD+34°198, FK5 42, GJ 53.3, 9044, HD 6860, HIP 5447, HR 337, SAO 54471, PPM 66010, WDS 01097+3537A, LTT 10420, NLTT 3848[7][15]
Database references
SIMBADdata

Mirach is a prominent star in the northern constellation of Andromeda. It is pronounced /ˈmaɪræk/[16][17] and has the Bayer designation Beta Andromedae, which is Latinized from β Andromedae. This star is positioned northeast of the Great Square of Pegasus and is potentially visible to all observers north of latitude 54° S. It is commonly used by stargazers to find the Andromeda Galaxy. The galaxy NGC 404, also known as Mirach's Ghost, is seven arcminutes away from Mirach.[18]

This star has an apparent visual magnitude of around 2.07,[1] varying between 2.01 and 2.10,[2] which at times makes it the brightest star in the constellation. Based upon parallax measurements, it is roughly 197 light-years (60 parsecs) from the Solar System.[10] Its apparent magnitude is reduced by 0.06 by extinction due to gas and dust along the line of sight.[9] The star has a negligible radial velocity of 0.1 km/s,[9] but with a relatively large proper motion, traversing the celestial sphere at an angular rate of 0.208″·yr−1.[19]

Properties

[edit]
A light curve for Mirach, plotted from Hipparcos data[20]

Mirach is a single,[21] aging red giant with a stellar classification of M0 III.[4] It is currently on the asymptotic giant branch of its evolution.[3] The star has an estimated 2.49 times the mass of the Sun.[12] Having exhausted the supply of hydrogen at its core, 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[13] at an effective temperature of 3,762 K.[14] Mirach is suspected of being a semiregular variable star, with an apparent visual magnitude varies from +2.01 to +2.10.[2] Since 1943 the spectrum of this star has been one of the stable anchor points by which other stars are classified.[22]

Nomenclature

[edit]

Beta Andromedae is the star's Bayer designation. 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),[23] which come from the star's description in the Alfonsine Tables of 1521 as super mizar. Here, mirat is a corruption of the Arabic مئزر mīzar "girdle", which appeared in a Latin translation of the Almagest.[15] This word refers to Mirach's position at the left hip of the princess Andromeda.[24] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[25] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[26] 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).[27] Medieval astronomers writing in Arabic called Mirach Janb al-Musalsalah (English: The Side of the Chained (Lady)); it was part of the 28th manzil (Arabian lunar mansion) Baṭn al-Ḥūt, the Belly of the Fish, or Qalb al-Ḥūt, the Heart of the Fish.[15][28] The star has also been called Cingulum and Ventrale.[15] This al-Ḥūt was an indigenous Arabic constellation, not the Western "Northern Fish" part of the constellation Pisces.[28] These names are not from the Arabic marāqq, loins, because it was never called al-Marāqq in Arabian astronomy.[28] 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.[15][29]

In Chinese, 奎宿 (Kuí Sù), 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, σ Piscium, τ Piscium, 91 Piscium, υ Piscium, φ Piscium, χ Piscium and ψ1 Piscium. Consequently, the Chinese name for β Andromedae itself is 奎宿九 (Kuí Sù jiǔ, English: the Ninth Star of Legs).[30] Mirach was considered the standard "black" star; black could mean "dark red" in this context, especially in comparison to Antares, the standard red star.[31]

The people of Micronesia named this star Kyyw, meaning "The Porpoise", and this was used as one of the names of the months in Micronesia.[32]

Substellar companion

[edit]

A 2023 study detected radial velocity variations in Mirach (HD 6860), showing evidence of a substellar companion, likely a brown dwarf.[5]

The Mirach planetary system[5]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b ≥28.26+2.05
−2.17 MJ 		2.03±0.01 663.87+4.61
−4.31 		0.28+0.10
−0.09 		— —

References

[edit]

Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Mirach

View on Grokipedia
from Grokipedia
Mirach, designated Beta Andromedae (β Andromedae), is a prominent in the constellation Andromeda, located approximately 197 light-years from . It shines with an apparent visual magnitude of 2.06, varying between 2.01 and 2.10, often ranking it as the second-brightest in its constellation after Alpha Andromedae (Alpheratz), though sometimes the brightest, and the 55th brightest in the , visible to the under clear conditions. Classified as an M0 IIIa spectral type giant, Mirach has a surface of about 3,762 , giving it a distinctive orange-red hue, and it possesses a mass estimated at about 2.5 times that of the Sun while expanding to a roughly 85 times the Sun's —equivalent to about 0.4 AU, roughly the orbit of Mercury. This evolved star emits around 1,700 times the luminosity of the Sun, though its light output shows slight semiregular variability. Mirach is accompanied by a faint 14th-magnitude companion star approximately 1,700 AU distant, which is a low-mass, hydrogen-fusing dwarf. Astronomically, it serves as a key guidepost for locating deep-sky objects, including the (M31) by extending a line from Mirach through Mu Andromedae, the (M33) in the opposite direction, and especially the lenticular galaxy NGC 404—nicknamed "Mirach's Ghost"—which lies just 7 arcminutes away and is visible in small telescopes despite its 11th-magnitude faintness. The name "Mirach" derives from an term meaning "the loin" or "the girdle," originally part of Andromeda's mythological depiction as a chained princess in Greek lore, though historical records show early confusions with the name "."

Nomenclature and Cultural Significance

Traditional Names and Etymology

The traditional name Mirach for Beta Andromedae derives from medieval astronomy, stemming from the word mīzar (مئزر), meaning "" or "loin cloth," which alludes to the star's position at the waist or hip of the constellation figure representing Andromeda. This nomenclature reflects the descriptive practices of early Islamic astronomers who mapped stars relative to mythological or human-like forms in the sky. Historical variants of the name include Merach, Mirac, Mirar, Mirath, and Mirak, arising from differences in Latin and European texts adapting sources. In medieval treatises, the star was also designated Janb al-Musalsalah (جَنْب الْمُسَلْسَلَة), translating to "the side of the chained lady," further highlighting its anatomical placement on Andromeda's chained posture in the asterism. The Beta Andromedae, assigned in the early , provided the foundation for adopting Mirach as the standardized proper name. On June 30, 2016, the (IAU), through its Working Group on Star Names (WGSN), officially approved Mirach as the proper name for this star, drawing from its long-established traditional usage to promote global consistency in astronomical . Beyond Arabic traditions, Mirach holds cultural significance in Micronesian societies, where it is known as Kyyw, meaning "the ," a name that also denoted one of the months in their and contributed to the employed by navigators for across the Pacific.

Astronomical Designations

Mirach holds the Beta Andromedae (β And), identifying it as the second-brightest star in the constellation Andromeda after Alpha Andromedae. It also bears the Flamsteed designation 43 Andromedae, assigned in the early 18th-century star atlas Historia Coelestis Britannica. In modern catalogs, Mirach is entry HD 6860 in the Henry Draper Catalogue, a comprehensive 20th-century compilation of stellar spectra and positions. Its equatorial coordinates in the J2000.0 epoch are 01ʰ 09ᵐ 43.92ˢ and +35° 37′ 14.0″. Additionally, the Hipparcos Catalogue designates it as HIP 5447, based on astrometric data from the 1990s ESA mission that refined positions for over 100,000 stars. The formally approved Mirach as the proper name for Beta Andromedae in 2016.

Role in Mythology and Navigation

In , Mirach (Beta Andromedae) forms a key part of the constellation Andromeda, representing the chained princess sacrificed to a as punishment for her mother Cassiopeia's ; the star specifically marks the waist or girdle of the figure, emphasizing her bound and vulnerable posture in ancient depictions. This positioning aligns with Ptolemy's second-century catalog, where Mirach is described as the southernmost of three stars draping over Andromeda's girdle, reinforcing the mythological narrative of captivity and rescue by . In Arabic astronomy, Mirach was integral to the "girdle" asterism within Andromeda, known as al-mi'zar (girdle or loincloth), and featured prominently in navigational star catalogs such as the Zij al-Sindhind and Abd al-Rahman al-Sufi's Book of Fixed Stars (ca. 964 CE), where it served as a reference for determining celestial positions during maritime voyages. Additionally, it formed the 28th lunar mansion (manzil), termed Baṭn al-Ḥūt (Belly of the Fish) or Qalb al-Hūt (Heart of the Fish), used by navigators like Ahmad ibn Majid in the 15th century to track lunar progress and orient ships across the Indian Ocean. Micronesian voyagers, particularly from the Carolinian islands, incorporated Mirach into their system for trans-Pacific , identifying it as part of the Igulig (whale) asterism where it represents the whale's body, aiding in directional orientation alongside swells and winds during long voyages. This usage was preserved and taught by master navigator of , who employed such stellar patterns to guide non-instrument voyages, including the 1976 Hōkūleʻa expedition from to . During the medieval period in , Mirach appeared in star atlases derived from sources, such as the 13th-century Latin translations of al-Sufi's work, where it helped locate the (now known as the ) as a "nebulous spot" near the girdle stars of the constellation's asterism. These references, illustrated in manuscripts with dotted markers, facilitated early European astronomers' identification of the nebula relative to Mirach's position, bridging Islamic and Western celestial traditions.

Physical Characteristics

Stellar Parameters

Mirach possesses an apparent visual magnitude of 2.067, rendering it the 54th brightest star in the night sky. The star lies at a of 197 ± 7 light-years from the Solar System, as determined by measurements from the mission. As a , Mirach has expanded dramatically, attaining a radius of 86.4 solar radii (R⊙R_\odot) and a of 2.49 solar masses (M⊙M_\odot). Its luminosity reaches 1,675 solar luminosities (L⊙L_\odot), derived from its measured and bolometric magnitude. The of Mirach's is 3,762 ± 40 K.

Spectral Classification and Atmosphere

Mirach is classified as an III in the Morgan-Keenan (MK) system, characterized by strong molecular absorption bands typical of cool, evolved red giants. This classification has remained stable since its establishment as a spectral standard in , serving as a reference point for classifying other late-type stars. The star's orange-red appearance arises from its relatively cool of 3,762 K, which shifts its peak emission into the while producing a hue in visible light. Prominent (TiO) absorption bands dominate its optical spectrum, particularly around 5900 Å and 6200 Å, contributing to the characteristic features of M-type giants. Mirach exhibits levels near solar, with an iron abundance of [Fe/H] ≈ -0.30, indicating a composition broadly similar to the Sun's despite slight depletion in heavier elements. As a , its atmosphere is expanded, resulting in low (log g ≈ 1.1), which influences the broadening of lines and the overall atmospheric structure.

Evolutionary Stage

Mirach is currently located on the (AGB) of its evolutionary track, a phase that follows the ascent of the (RGB), during which the experiences thermal pulses driven by helium shell fusion surrounding an inert carbon-oxygen core. This stage marks a period of instability and enhanced loss as the 's envelope expands dramatically. The 's progenitor was a main-sequence A-type with an initial of approximately 2.5 solar masses, from which it evolved roughly 100 million years ago after exhausting its core hydrogen fuel. models for such intermediate- stars place Mirach's total age at 0.5–1 billion years. Looking ahead, Mirach will continue to expand into a , intensifying its stellar winds and shedding outer layers, ultimately ejecting material to form a while leaving a remnant as its core cools. Its substantial radius and underscore this late giant phase in the star's lifecycle.

Variability and Orbital Properties

Semiregular Variability

Mirach is classified as a suspected , typical for late-type giants exhibiting irregular or poorly defined pulsational cycles. This type is characterized by small-amplitude brightness variations without a dominant periodicity, often spanning periods longer than 30 days but lacking consistent repetition. The star's apparent visual magnitude shows fluctuations of 0.09 magnitudes, ranging from +2.01 to +2.10, as reported in observational catalogs. These variations arise from intrinsic pulsations associated with the star's status on the , where thermal instabilities and convective motions in the extended envelope drive irregular expansions and contractions. Long-term monitoring by the American Association of Observers (AAVSO) has documented these irregular changes through visual and photometric observations spanning decades, confirming the lack of a stable period despite short-term fluctuations around 41 days noted in some datasets. The modest amplitude of Mirach's variability ensures that it remains steadily visible to the , with changes too subtle to be discerned without instrumental aid, preserving its utility as a reliable guide star in the constellation Andromeda.

Proper Motion and Space Velocity

Mirach has a of 175.90 mas/year in and -112.20 mas/year in , according to data from the DR3 catalog. This transverse motion across the sky corresponds to a tangential of approximately 60 km/s at its distance of about 61 pc, providing insight into the star's path through the local stellar neighborhood. The of Mirach is measured at +0.06 ± 0.13 km/s, indicating negligible motion along the relative to the Solar System. Combining this with the yields space velocity components relative to the local standard of rest that position Mirach on a typical within the Way's , characterized by low eccentricity and no substantial peculiar motion that might indicate dynamical influences from an undetected massive companion beyond the known substellar object.

System Components

Stellar Companion

Mirach has a faint visual companion, a low-mass hydrogen-fusing dwarf star with an apparent magnitude of 14, located at a projected separation of approximately 1,700 AU. This companion is over 60,000 times less luminous than Mirach and is visible in moderate-sized telescopes. The nature of their orbit is not fully determined, but they form a wide binary system.

Substellar Companion

In 2023, a substellar companion to Mirach (Beta Andromedae, HD 6860) was discovered through long-term radial velocity monitoring conducted at the Bohyunsan Observatory using the high-resolution Bohyunsan Observatory Echelle Spectrograph (BOES). This detection revealed periodic variations in the star's radial velocity, confirming the presence of an orbiting substellar object with a minimum mass of 28.26−2.17+2.0528.26^{+2.05}_{-2.17} Jupiter masses (MJM_J), placing it firmly in the brown dwarf regime given the hydrogen-burning mass limit of approximately 13 MJM_J. The companion's orbit was characterized using a Keplerian model fitted to 44 high-precision spectra spanning from December 2005 to December 2021, yielding an of 663.87−4.31+4.61663.87^{+4.61}_{-4.31} days, a semi-major axis of 2.03−0.01+0.012.03^{+0.01}_{-0.01} AU, and an eccentricity of 0.28−0.09+0.100.28^{+0.10}_{-0.09}. These parameters were derived via simulations, assuming a host star mass of 2.49 solar masses (M⊙M_\odot), which scales the companion's gravitational influence on the primary's motion. No direct of the companion has been achieved to date, limiting confirmation of its true mass and inclination, though the minimum mass suggests a likely nature rather than a . This discovery highlights the potential for substellar companions around evolved M giants like Mirach, contributing to understanding companion survival during stellar expansion.

Association with Nearby Celestial Objects

Mirach, the bright red giant star Beta Andromedae, appears in close visual proximity to the NGC 404, separated by an of about 7 arcminutes. This faint object, with an of 10.3, is often obscured by Mirach's glare in visible light, earning it the nickname "Mirach's Ghost." The was discovered by in 1784, who described it as a nebulous patch near the star. NGC 404 lies approximately 10 million light-years distant, far beyond Mirach's own distance of 197 light-years, confirming no physical connection and attributing their alignment to a mere line-of-sight coincidence.

Observation and Significance

Visibility and Location in the Sky

Mirach, also known as Beta Andromedae, occupies a prominent position in the constellation Andromeda, lying approximately halfway along the figure's "body" between the stars Alpheratz (Alpha Andromedae) and Almach (). It appears just below the northeastern side of the Great Square asterism in the neighboring constellation , making it a distinctive orange-red point of light in that region of the sky. This second-magnitude star is easily visible to the from all locations north of about 54° south , owing to its of approximately +35.6°. For observers in the , Mirach culminates—reaching its highest point in the sky—around , when it transits the meridian near . It is best observed during autumn evenings, from through , when the constellation rises early in the evening and arcs high overhead. In mid-northern latitudes (around 40° to 50° N), Mirach can reach altitudes of approximately 76° to 86° above the horizon at , providing excellent viewing conditions with minimal atmospheric distortion. Its apparent visual magnitude of 2.06 ensures minimal interference from , allowing detection even in suburban skies, though darker sites enhance the experience. For precise locating with star charts or apps, Mirach's equatorial coordinates are 01h 09m 44s and +35° 37'.

Use as a Guide Star

Mirach serves as a primary guide star for locating the (M31), one of the most prominent deep-sky objects visible to amateur astronomers. M31 lies approximately 8° northwest of Mirach and can be located by star-hopping from Mirach northwest about 3.5° to the magnitude 4.5 star ν Andromedae, then continuing a similar distance further northwest; this positions M31 as a faint fuzzy patch accessible even under moderate with or the on clear nights. The star also aids in spotting other nearby galaxies using or small telescopes. For the (M33), a fainter spiral, one extends a line from Mu Andromedae through Mirach and continues roughly twice that distance, revealing M33 as a challenging but rewarding target for . Similarly, NGC 404—known as Mirach's due to its proximity—lies just 7 arcminutes north of the star, allowing contextual pointing in telescopic setups where the bright Mirach helps frame the faint for observation. In , Mirach's magnitude 2.06 brightness and strategic position facilitate field alignment and focusing for imaging nearby objects, such as NGC 404, which has been captured using modest equipment like 120 mm refractor telescopes centered on the star. Recent observations in 2025 highlighted Mirach's utility when C/2025 F2 (SWAN) passed just south of it in April, enabling observers to track the comet's path eastward through Andromeda by using the star as a reference point in the morning sky.

References

  1. https://www.stellarcatalog.com/stars/beta-andromedae
  2. https://theskylive.com/sky/stars/mirach-beta-andromedae-star
  3. https://www.star-facts.com/mirach/
  4. https://nineplanets.org/mirach/
  5. https://earthsky.org/brightest-stars/mirach-guide-star-to-three-galaxies/
  6. http://stars.astro.illinois.edu/sow/mirach.html
  7. http://judy-volker.com/StarLore/Myths/AncientMiddleEast_A-D.html
  8. https://iauarchive.eso.org/public/themes/naming_stars/
  9. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=Beta+Andromedae
  10. http://www.ianridpath.com/startales/andromeda.html
  11. https://www.constellationsofwords.com/mirach/
  12. https://rutter-project.org/wp-content/uploads/2021/09/acevedo_benard_tn8.pdf
  13. https://www.perditaphillips.com/curiosity/curious-facts/star-compass-from-the-knowledge-of-pius-mau-piailug-834/
  14. https://hokulea.com/polynesian-wayfinding/
  15. https://www.eso.org/sci/publications/messenger/archive/no.49-sep87/messenger-no49-42-43.pdf
  16. https://ui.adsabs.harvard.edu/abs/2017MNRAS.471..770M/abstract
  17. https://www.aanda.org/articles/aa/full_html/2023/10/aa43725-22/aa43725-22.html
  18. https://arxiv.org/abs/1812.07185
  19. https://doi.org/10.1051/0004-6361/202243725
  20. https://apod.[nasa](/page/NASA).gov/apod/ap031029.html
  21. https://academic.oup.com/mnras/article/496/4/4061/5870560
  22. https://www.skyatnightmagazine.com/advice/mirach
  23. https://lovethenightsky.com/andromeda-constellation-guide/
  24. https://www.skyledge.net/Messier31-hop.htm
  25. https://www.astronomy.com/observing/c-2025-f2-swan-a-new-comet-is-in-the-spring-sky/
  26. https://www.skyatnightmagazine.com/news/c-2025-f2-swan
Add your contribution
Related Hubs
User Avatar
No comments yet.