Markab is Alpha Pegasi, a blue-white star at about 133 light years, and it marks the southwestern corner of the Great Square of Pegasus, the large and useful rectangle of stars that dominates the autumn sky. Its name, from the Arabic markab, means a saddle, a mount or a vehicle, the place on the winged horse where a rider would sit, an apt name for a star set on the body of Pegasus. With Scheat, Algenib and the shared star Alpheratz it forms the four corners of the Square, one of the most recognisable patterns in the northern heavens.
The Great Square's four corners, Markab, Scheat, Algenib and the shared Alpheratz, are not all equally bright, and Alpheratz's eventual reassignment wholly to Andromeda left the Square's fourth corner permanently borrowed from a neighbouring constellation, a quirk that makes the Square, for all its usefulness as a signpost, technically not a figure contained within Pegasus alone under the modern boundaries. No delineation earlier than the compiling tradition survives for Markab specifically beyond the general character Ptolemy gives Pegasus as a whole, the ordinary situation for a corner star of an otherwise well-known asterism. Markab's position at a corner of so widely recognised a pattern has made it one of the more useful practical signposts for amateur observers new to the autumn sky.