Alpheratz

Alpheratz, also designated as Alpha Andromedae (α And / α Andromedae), is the brightest star in the constellation Andromeda. It was historically considered to be part of both Andromeda and the constellation Pegasus, where it was designated Delta Pegasi (δ Peg / δ Pegasi). Its dual membership reflected its location near the intersection of the two constellations.

Properties:

Alpheratz is a binary star system located approximately 97 light-years from Earth. The primary component, Alpha Andromedae A, is a mercury-manganese star, a chemically peculiar star with strong spectral lines of mercury, manganese, silicon, and chromium in its atmosphere. These elements appear in unusual abundances due to radiative diffusion, a process where certain elements are supported by radiation pressure while others sink below the surface layer. Alpha Andromedae A is also a hot, rapidly rotating star, classified as a B8 IVpMnHg star, indicating it is a B-type subgiant.

The secondary component, Alpha Andromedae B, is a much fainter, cooler star and little is currently known about its characteristics.

Nomenclature:

The name "Alpheratz" is derived from the Arabic name Al Surrat al Faras, meaning "the navel of the mare," referring to its historical association with Pegasus, the winged horse. The name reflects its former location within the constellation. Other historical names include Sirrah, a shortened version of the same Arabic phrase.

Historical Significance:

Due to its brightness, Alpheratz has been an important navigational star for centuries. It also holds cultural significance in various mythologies and astronomical traditions. Its location at the corner of the Great Square of Pegasus made it a prominent marker in the night sky. Following the standardization of constellation boundaries in the 20th century, Alpheratz was definitively assigned to Andromeda.