Alpheratz is Alpha Andromedae, apparent magnitude 2.06, at about 97 light years. It is a blue-white subgiant, and chemically a mercury-manganese star, its atmosphere showing anomalous over-abundances of those and other heavy elements. It marks the northeastern corner of the Great Square of Pegasus and was historically shared between the two constellations, once catalogued as Delta Pegasi before the boundaries were fixed and it was assigned wholly to Andromeda. The Arabic name, surrat al-faras, means the navel of the horse, of Pegasus, not of Andromeda, a reminder that the star belonged to the horse before it belonged to the chained woman.
Alpheratz's Arabic name is a genuine case of a popular etymology gone wrong: it is often glossed loosely as simply "the horse", but surrat al-faras parses precisely as surrat, navel, plus al-faras, the horse, a compound descriptive phrase rather than a single proper name, of exactly the kind the older Arabic star catalogues favour over invented names. Ptolemy catalogued the star in the Almagest as of the second magnitude, close to its true modern value of 2.06, one of the cases where the ancient and modern brightness classes agree well; the star's slow drift in catalogued position across two millennia is precession, not any real change in the star itself.