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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

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


Orion’s Belt

orion the hunter

Photo taken by Rogelio Bernal Andreo in October 2010 of the Orion constellation showing the surrounding nebulas of the Orion Molecular Cloud complex. Also captured is the red supergiant Betelgeuse (top left) and the famous Belt of Orion. To the bottom right can be found the star Rigel. The red crescent shape is Barnard’s Loop.

Orion’s Belt is an asterism consisting of three bright stars in a straight line located in the Orion constellation. It is part of the larger hourglass-shaped asterism that makes Orion one of the easiest constellations to find in the night sky.

The three stars that form the Belt of Orion are Alnitak (Zeta Orionis), Alnilam (Epsilon Orionis) and Mintaka (Delta Orionis).

Alnitak is a triple star 736 light years from Earth that has a blue supergiant star as the primary component. The supergiant is the brightest star belonging to the spectral class O in the sky.

Alnilam is also a blue supergiant and the 30th brightest star in the sky. It lies in the middle of Orion’s Belt. It lies approximately 1,300 light years from Earth.

Mintaka is the right-most star in the asterism. It is in fact a multiple star system. The primary component is a binary star composed of a B-class giant and an O-class star. The stars are approximately 900 light years distant from the Sun.

orion belt,orion constellation

Alnitak, Alnilam, and Mintaka, are the bright bluish stars from east to west (left to right) along the diagonal in this gorgeous cosmic vista. Otherwise known as the Belt of Orion, these three blue supergiant stars are hotter and much more massive than the Sun. Image: Astrowicht