Pegasus is the seventh largest constellation in the night sky and belongs to the Perseus family of constellations. It is named after a mythical winged horse from greek mythology in which Zeus used the horse to carry his thunder and lightning.
The shape of the Pegasus Constellation includes only the front half of the horse. The body of the horse is represented by a large square formed by four stars, known as the Great Square of Pegasus asterism.
Pegasus is famous for being the first constellation to have an exoplanet. Though it is not included in the stars that make up the shape of the winged-horse constellation, 51 Pegasi was the first ever sun-like star discovered that had an exoplanet, 51 Pegasi b.
The constellation Pegasus rises in the eastern horizon.
Symbolism: Winged Horse
Brightest Star: Epsilon Pegasi
Number of stars: 12 stars with planets
Size: 1,121 sq. deg. (7th largest)
Right Ascension: 21h 12.6m to 00h 14.6m
Declination: +2.33° to +36.61°
Pegasus Constellation Stars
Bayer had originally cataloged 23 stars in this constellation, which all received Bayer designations.
Below are the main stars that make up the winged-horse shape of the Pegasus constellation according to the International Astronomical Union (IAU).
- Epsilon Pegasi (Enif): muzzle
- Theta Pegasi (Biham): eye
- Zeta Pegasi (Homam): neck
- Xi Pegasi: neck
- Alpha Pegasi (Markab): back
- Gamma Pegasi (Algenib): wing
- Beta Pegasi (Scheat): shoulder
- Mu Pegasi (Sadalbari): upper right arm
- Lambda Pegasi: mid right arm
- Iota Pegasi: lower right arm
- Eta Pegasi (Matar): left arm
- Pi Pegasi: left hoof
Pegasus Constellation | IAU
The brightest stars in the Pegasus constellation are:
- Enif (Epsilon Pegasi): an orange supergiant star that is the brightest star in the constellation with a visual magnitude of 2.399.
- Scheat (Beta Pegasi): a red giant star that is the second brightest star that is 1,500 more luminous than the Sun.
- Markab (Alpha Pegasi): a blue giant star that is the third brightest star that is enlarging and cooling to eventually become a red giant.
Alpheratz (formally Sirrah/Delta Pegasi) was originally considered a shared star between Pegasus and Andromeda until the IAU standardized the boundaries of the constellations.
Since then, the star is now considered part of the Andromeda constellation and is named ‘Alpha Andromedae’ or Alpheratz. It is one of four stars that form the square body of the horse, which is known as the Great Square of Pegasus.
The Great Square of Pegasus
The Great Square of Pegasus is an asterism that dominates the autumn sky in the northern hemisphere. It is made up of four stars, three of which are part of the winged-horse constellation Pegasus.
The stars that make up the Great Square are:
- Alphgeratz (from the Andromeda constellation)
Observers can use the Great Square to aid in finding other constellations and objects in the night sky including the Andromeda galaxy.
You can also use Alpheratz, the star that joins the Pegasus to Andromeda constellations, to find Andromeda. From Alpheratz, there are two ‘streams’ of stars extending in the opposite direction of the Great Square as part of the Andromeda constellation. Find Mirach and Mu, and connect them with a vertical line through both stars that points to Andromeda.
How to find the Pegasus Constellation
An easy way to locate Pegasus is to look for the Great Square of Pegasus.
You can also use the ‘pointer stars’ (i.e. Merak and Dubhe) in the Big Dipper, which are typically used to help find Polaris. Use the pointer stars to draw an imaginary line through Polaris, past Caph in Cassiopeia to reach Pegasus.
The constellation is also surrounded by several other constellations, including Cygnus (northwest), Andromeda (north and east), Aquarius (south), Pisces (south and east), and Vulpecula, Delphinus and Equuleus (west).
When is Pegasus Visible?
In the northern hemisphere, the Pegasus constellation is visible near the end of summer through autumn. If you are below the equator, look for Pegasus in late winter through spring.
The month of October is the best time to view the constellation in the northern hemisphere. Look to the eastern horizon on autumn evenings with the constellation nearing overhead by late fall.
Deep-sky Objects in the Pegasus Constellation
There are a number of deep-sky objects in the constellation Pegasus, below are a few noteworthy targets.
- M15 (NGC 7078): a dense globular cluster located near the stars that make up the head and neck of Pegasus. At 6.4 magnitude, and a distance of approximately 33,600 light-years away, you can spot this target using a pair of binoculars. It is one of the oldest known globular clusters, believed to be 12 billion years old.
- NGC 7742: an unbarred spiral galaxy seen face-on. This galaxy is unique in that with its ring there is no bar which is typically needed to produce a ring structure. This suggests the galaxy was formed another way, perhaps through a collision with a smaller gas-rich dwarf galaxy.
- Stephan’s Quintet: is a cluster of five galaxies (NGC 7317-7320) at a distance of about 280 million light-years away. It is said to be the most studied of all compact galaxy groups. The brightest galaxy of the group is NGC 7320 which has large HII regions of active star formation.
- Einstein Cross: is a gravitationally lensed quasar that is approximately 8 billion light-years away. According to NASA, the unique shape of this object is caused by “the light from the quasar which is bent to produce four bright in its path by the gravitational field of the galaxy. This bending has produced the four bright outer images seen in the photograph.”
In Greek mythology, Pegasus is an immortal winged horse that sprang from the neck of Medusa after she was beheaded by Perseus. He became the horse for Bellerophon, the greatest hero and slayer of monsters. Eventually Bellerophon would ask Pegasus to take him to Mount Olympus, which angered Zeus. Pegasus would arrive to Olympus alone and would eventually be stabled by Zeus and tasked with drawing the chariot of his thunderbolts.
In Hindu culture, the Great Square of Pegasus represented a resting place for the Moon.