The Great Square of Pegasus

The Great Square of Pegasus is a well-known asterism in Pegasus constellation formed by three stars in Pegasus – Markab (Alpha Pegasi), Scheat (Beta Pegasi), and Algenib (Gamma Pegasi) – and Alpheratz (Alpha Andromedae), the brightest star in Andromeda constellation.

Markab is a class B giant star with a radius almost five times that of the Sun, about 133 light years distant from the solar system.

Scheat is the second brightest star in Pegasus. It is a red giant or subgiant star approximately 196 light years distant from Earth.

Algenib is a B class subgiant about nine times more massive than the Sun. It is approximately 390 light years distant from Earth.

Alpheratz (sometimes also known as Sirrah) is a double star, with two components closely orbiting each other. The star used to be known as Delta Pegasi, but is now treated as a star in Andromeda constellation. It is about 97 light years distant.

The Great Square of Pegasus can be seen rising above the horizon in the eastern sky in late September.

The Great Square of Pegasus and Pegasus constellation. Image: fdecomite at wikipedia.org

The Great Square of Pegasus and Pegasus constellation. Image: fdecomite at wikipedia.org

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