Pegasus, a constellation in the northern sky, was one of the 48 constellations listed by the 2nd-century astronomer Ptolemy.
In the Northern Hemisphere, the constellation is high in the sky starting near the end of summer and continuing through autumn. If you are below the Equator, look for Pegasus in late winter and through spring.
The stars α Peg (also known as Markab), β Peg, and γ Peg, and α Andromedae (Alpheratz or Sirrah) form the large asterism known as the Square of Pegasus. The front legs of the winged horse are formed by two crooked lines of stars, one leading from η Peg to κ Peg and the other from μ Peg to 1 Pegasi. Another crooked line of stars form the neck and head.
The brightest star in the constellation is Enif (ε Peg), which forms the nose.
The star Scheat forms the foreleg and the star Algenib, Arabic for wing, defines the wing. Although Algenib’s luminosity is 1,900 times greater than the Sun, it is seen only at a magnitude 2.8 because it is 570 light-years away.
Another star in this constellation, 51 Pegasi, is the first Sun-like star known to have a planet orbiting around it.
Clusters of galaxies
Among Pegasus’ more remarkable features are its numerous galaxies and objects.
A Messier object, M15, is a globular cluster of magnitude 6.4 about 34,000 light-years from Earth. It is one of the most densely packed clusters in the Milky Way galaxy.
NGC 7331 is a spiral galaxy about 38 million light-years away. It was one of the first objects to be described as "spiral."
Einstein's Cross, a quasar, is an excellent example of gravitational lensing. The quasar is about 8 billion light-years from Earth, and sits behind a galaxy that is 400 million light-years away. Four images of the quasar appear around the galaxy because the intense gravity of the galaxy bends the light coming from the quasar.
Stephan's Quintet is actually a cluster of five galaxies that is 300 million light-years away.
Pegasus is best seen in October, at 9 p.m. local time.
- Right ascension: 22 hours
- Declination: 20 degrees
- Visible between latitudes 90 and -60 degrees
The name comes from the winged white horse that was the sire of Poseidon in Greek mythology. The story of Pegasus begins with a battle between Perseus and Medusa. One day the warrior Bellerophon tried to ride Pegasus to Mount Olympus, enraging Zeus so much that he sent a gadfly to bite Pegasus. When the horse was stung, Bellerophon fell to the Earth. Pegasus made it to Olympus. [How the Night Sky Constellations Got Their Names]
— Kim Ann Zimmermann
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