Beta Andromedae

Beta Andromedae

Location of β Andromedae (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Andromeda
Right ascension	01h 09m 43.92388s[1]
Declination	+35° 37′ 14.0075″[1]
Apparent magnitude (V)	2.05[2] (2.01 to 2.10)[3]
Characteristics
Spectral type	M0 III[4]
U−B color index	+1.96[2]
B−V color index	+1.57[2]
V−R color index	0.9[5]
R−I color index	+1.00[6]
Variable type	Semiregular[3]
Astrometry
Radial velocity (Rv)	0.06 ± 0.13[7] km/s
Proper motion (μ)	RA: 175.90[1] mas/yr Dec.: −112.20[1] mas/yr
Parallax (π)	16.52 ± 0.56[1] mas
Distance	197 ± 7 ly (61 ± 2 pc)
Absolute magnitude (MV)	–1.76[8]
Details
Mass	3–4[9] M☉
Radius	100[10] R☉
Luminosity	1,995[10] L☉
Surface gravity (log g)	1.52[11] cgs
Temperature	3,842[11] K
Metallicity [Fe/H]	–0.05[11] dex
Rotational velocity (v sin i)	7.2[10] 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, GJ 9044, HD 6860, HIP 5447, HR 337, LTT 10420, NLTT 3848, SAO 54471, WDS 01097+3537A.[5][12]
Database references
SIMBAD	data

Beta Andromedae (β Andromedae, abbreviated Beta And, β And), also named Mirach,^[13] is a prominent star in the northern constellation of Andromeda. It is located northeast of the Great Square of Pegasus and is theoretically visible to all observers north of 54° S. It is commonly used by stargazers to find the Andromeda Galaxy. The galaxy NGC 404, also known as Mirach's Ghost, is visible seven arc-minutes away.^[14]

This star has an average apparent visual magnitude of 2.05,^[2] which makes it the brightest star in the constellation. However, the luminosity varies slightly from magnitude +2.01 to +2.10.^[3] Based upon parallax measurements, it is located at a distance of roughly 197 light-years (60 parsecs) from the Sun.^[1] The apparent magnitude of this star is reduced by 0.06 from extinction caused by the gas and dust along the line of sight.^[7]

Properties

Relative sizes of the components to the Sun (top right). Circle sizes relate to solar radii, italic numbers are solar mass estimates to 4SF.

Beta Andromedae is a red giant with a stellar classification of M0 III.^[4] Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.^[15] It is suspected of being a semiregular variable star whose apparent visual magnitude varies from +2.01 to +2.10.^[3] At this stage of the star's evolution, the outer envelope has expanded to around 100 times the size of the Sun.^[10] It is radiating 1995^[10] times the luminosity of the Sun at an effective temperature of 3842 K.^[11]

Nomenclature

• 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),^[16] which come from the star's description in the Alfonsine Tables of 1521 as super mizar. Here, mirat is a corruption of the Arabic ميزر mīzar "girdle", which appeared in a Latin translation of the Almagest.^[12] This word refers to Mirach's position at the left hip of the princess Andromeda.^[17]
• In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)^[18] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016^[19] included a table of the first two batches of names approved by the WGSN; which included Mirach for this star.
• Medieval astronomers writing in Arabic called β Andromedae Janb al-Musalsalah (English: The Side of the Chained (Lady)); it was part of the 26th manzil (Arabian lunar mansion) Baṭn al-Ḥūt, the Belly of the Fish, or Qalb al-Ḥūt, the Heart of the Fish.^[12][20] The star has also been called Cingulum and Ventrale.^[12] This al-Ḥūt was an indigenous Arabic constellation, not the Western "Northern Fish" part of the constellation Pisces.^[20] These names are not from the Arabic marāqq, loins, because it was never called al-Marāqq in Arabian astronomy.^[20] Al Rishā', the Cord (of the well-bucket), on al-Sūfī's star map. It is origin of the proper name Alrescha for Alpha Piscium.^[12][21][22]
• In Chinese, 奎宿 (Kuí Sù), meaning Legs (asterism), refers to an asterism consisting of 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, β Andromedae itself is known as 奎宿九 (Kuí Sù jiǔ, English: the Ninth Star of Legs.)^[23]
• The people of Micronesia named this star as Kyyw "The Porpoise", and become once of Micronesian month name.^[24]
• Mirach is listed in MUL.APIN as KA.MUSH.I.KU.E, meaning "the Deleter" (the alternative star is α Cas).^[25]

References

Further reading

• Davis Jr., G. A., (1971) Pronunciations, Derivations, and Meanings of a Selected List of Star Names, (rep.) Cambridge, Sky Publishing Corp.
• Kunitzsch, P., (1959) Arabische Sternnamen in Europa
• Kunitzsch. P., (ed.) (1990) Der Sternkatalog des Almagest, Band II

External links

• Image MIRACH
• Beta Andromedae on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Coordinates: 01^h 09^m 43.9236^s, +35° 37′ 14.008″