Alpha Andromedae

Alpha Andromedae (Alpha And, α And, α Andromedae), which has the traditional names Alpheratz (or Alpherat) and Sirrah (or Sirah), is the brightest star in the constellation of Andromeda. Located immediately northeast of the constellation of Pegasus, it is the northeastern star of the Great Square of Pegasus. As a connecting star to Pegasus, it is also known as δ Pegasi, though this name is no longer used (another such doubly named connecting star is β Tauri). It is located 97 light-years from Earth. Although it appears to the naked eye as a single star, with overall apparent visual magnitude +2.06, it is actually a binary system composed of two stars in close orbit. The chemical composition of the brighter of the two stars is unusual as it is a mercury-manganese star whose atmosphere contains abnormally high levels of mercury, manganese, and other elements, including gallium and xenon. It is the brightest mercury-manganese star known.

This star has for long been treated as being in Pegasus and simultaneously in Andromeda, and Johann Bayer catalogued it as both α Andromedae and δ Pegasi.