Mirach (Beta Andromedae)

Mirach (Beta Andromedae) is the joint equal brightest star (with Alpheratz) in the constellation Andromeda. A giant M star, Mirach measures about 0.8 astronomiical units (AU) across or roughly the size of Mercury's orbit. Its core may be largely filled with helium or with carbon; whatever the state, it will soon die as a dense white dwarf. Like many cool red giants, Mirach seems to be slightly variable, though the variations are not well documented. It also has a low-mass main-sequence companion, of only 14th magnitude, that is over 60,000 times fainter than Mirach proper. At minimum, the two are 1,700 AU apart, over 40 times Pluto's average distance from the Sun.


visual magnitude 2.07
absolute magnitude -1.87
spectral type M0IIa
surface temperature 3,800 K
luminosity 1,900 Lsun
mass 3 to 4 Msun
distance 199 light-years
position RA 01h 09m 43.9s,
Dec +35° 37' 14"