Beta Andromedae

Beta Andromedae, officially named Mirach is a star in the northern constellation of Andromeda. It is located northeast of the Great Square of Pegasus and is commonly used by stargazers to find the Andromeda Galaxy. The galaxy NGC 404, also known as Mirach's Ghost, is seven arc minutes away from Mirach.

This star has an apparent visual magnitude of 2.05, making it the second brightest star in Andromeda. The luminosity varies slightly from magnitude +2.01 to +2.10. Based upon parallax measurements, it is roughly 197 light-years from the Sun. Its apparent magnitude is reduced by 0.06 by extinction due to gas and dust along the line of sight.

Name
Beta Andromedae (abbreviated to β And) is the star's bayer designation, a stellar designation where a greek letter is followed by the genitive form of its constellation name. Its official or tradition name, Mirach or Mirac and many other corruptions (Mirar, Mirath, Mirak, Merach) comes from the star's description in the Alfonsine Tables of 1521 as super mizar. Mirach and the other names are corruptions of the word مئزر mizar which means "girdle". The name Mizar was given to another star which bayer designation is ζ Ursae Majoris.

Medieval astronomers called this star Janb al-Musalsalah (English: The Side of the Chained Lady). The star has also been called Cingulum and Ventrale. 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. 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.

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, the Chinese name for β Andromedae itself is 奎宿九 (Kuí Sù jiǔ, English: the Ninth Star of Legs.)

Properties
Beta Andromedae is a red giant with a stellar classification of M0 III. Since 1943, the spectrum of this star has been one of the stable anchor points by which other stars are classified. It is a semiregular variable star whose apparent visual magnitude varies from +2.01 to +2.10. Because of this, there is confusion whether Alpheratz or Mirach is the brightest star in the constellation. At this stage of the star's evolution, the outer envelope has expanded to around 100 times the size of the Sun. It is radiating 1995 times the luminosity of the Sun at a temperature of 3,842 K.

Position
The location of Mirach in the sky is shown on the left. It is theoretically visible to all observers north of 54° S. It is commonly used by stargazers to find the Andromeda Galaxy.

Its coordinate is around 01h 09m 43.9236s, +35° 37′ 14.008″.