Alpheratz, or α Andromedae, is the brightest star in the Andromeda constellation, which is located immediately northwest of Pegasus. As a connecting star to Pegasus, it is also known as Delta Pegasi, though this name is rarely used. It is located 97 light years from Earth, at a declination of +28d 32m 18s and a right ascension of 00h 03m 13.0s.

A magnitude 2.2 blue-white binary, Alpheratz is composed of two close-orbiting stars that can be distinguished only by careful spectroscopic analysis. The largest of the two is about ten times the size of the smaller, and they orbit each other with a period of 96.7 days. Classified as spectral-type B8, the pair is about 200 times brighter than the Sun, and has a surface temperature of about 13,000 Kelvin.

The larger of the two stars comprising Alpheratz is the brightest known of an odd group of stars known as "mercury-magnesium stars." It displays anomalously high abundances of mercury, gallium, manganese, and europium in its atmosphere, and unusually low abundances of other elements. These anomalies are believed to be the result of separation of elements due to the inward pull of the star's gravity.

Alpheratz is also known as Sirrah or Sirah after the original ancient Arabic name, Al Surrat al Faras (the Horse's Navel).

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