Mirach

Mirach is Beta Andromedae, apparent magnitude about 2.05, at roughly 197 light years. It is a red giant of spectral type M0, cooler and vastly larger than the Sun, and it varies slightly and irregularly as red giants do. It sits at the hip of Andromeda and serves observers as a signpost: a line through Mirach points toward both the Andromeda Galaxy and the smaller Triangulum Galaxy. A faint lenticular galaxy, NGC 404, lies so close to the star in the sky that it is nicknamed Mirach's Ghost, an unrelated background object glimpsed past the foreground glare.

At magnitude 2.05 it sits almost exactly on the traditional boundary between Ptolemy's first and second magnitude classes, and indeed ancient sources are not perfectly consistent about which class they place it in, a reminder that the six-step Hellenistic magnitude scale was always a judgment by eye rather than a measured quantity, and stars near a class boundary could be sorted differently by different observers centuries apart. Modern photometry places it steady at 2.05 without the variability sometimes claimed for it in older amateur reports, which most likely arose from comparison-star error rather than any real change in the star.

The tradition assigns Mirach the nature of Venus, reading it for personal charm, love of company, marriage and success won through others, a delineation that comes principally from Robson and the nineteenth-century sources he compiled rather than from any second-century text. The name has nothing to do with any of this: Mirach descends through Arabic and a scribal path from a word for a girdle or loincloth, marking the star's place on the figure. Its astrological reputation is entirely of the benefic, Venusian kind, with none of the martial or Saturnine menace attached to the red stars nearer the ecliptic.

Mirach anchors one of the more useful practical asterisms for locating deep-sky objects: a line drawn from Mirach through the fainter Mu Andromedae, extended the same distance again, lands almost exactly on the Andromeda Galaxy, a star-hopping method amateur observers have used for generations before digital go-to telescopes made the search trivial. The girdle sense of the name is shared with Zosma in Leo and Mirzam near Sirius, part of a small family of Arabic star-names built on the same word for a belt or waistband, applied to quite different constellations by different compilers.