Pegasus Constellation

The Pegasus Constellation resides in the Northern Hemisphere. First cataloged by Claudius Ptolemy, an ancient Greek mathematician and astronomer, today, Pegasus is recognized as the seventh largest of the International Astronomical Union’s (IAU) 88 constellations. This constellation resides south of Cassiopeia.

How Did Pegasus Constellation Get Its Name? 

This massive constellation got its name from Greek mythology’s magical, winged horse, Pegasus. It is generally pictured upside down in relation to the surrounding constellations, with its nose star Enif shining brightly at the lower right.  

Pegasus Constellation
Image Credit: WikiCommons

The Pegasus Constellation Details

A constellation is a named area in the sky with visible stars inside it. Ancient astronomers grouped stars into “figures” to commonly address specific celestial locations. Since constellations remain in virtually the same area for many years, they form astronomical landmarks for scientists.

The Pegasus Constellation hosts many fascinating deep-sky objects within its vast boundaries.  

  • Name: Pegasus, The Winged Horse
  • Type: Constellation
  • Size: 7th largest of the 88 known constellations
  • Brightest Star: Epsilon Pegasi, also called Enif
  • Distance From Earth: Enif is about 690 light-years away from Earth
  • Contains 1st Sun-like star (51 Pegasi) to host an exoplanet outside the Solar System. (An exoplanet is any planet that’s located outside our own solar system.)

Pegasus Constellation Characteristics

How Big Is the Pegasus Constellation?

Pegasus is the seventh largest of the 88 known constellations. It covers 1121 square degrees, the scale measure for all celestial areas. 

Given the three-letter designation “Peg” by the IAU in 1922, Pegasus is bordered by 

  • Andromeda to the north and east
  • Lacerta to the north
  • Cygnus to the northwest
  • Vulpecula, Delphinus and Equuleus to the west
  • Aquarius to the south
  • Pisces to the south and east.

How Old is the Pegasus Constellation?

Pegasus is one of the oldest known constellations. Ptolemy listed it in his group of 48 constellations during the second century. Earlier, Babylonians mentioned the Pegasus Constellation as containing a field with four bright stars. 

Neighbors of Pegasus

Pegasus belongs to the Perseus Constellation family, whose members include:

  • Andromeda
  • Auriga
  • Cassiopeia
  • Cephus
  • Cetus
  • Lacerta
  • Perseus
  • Triangulum

Where Is the Constellation Pegasus Located?  

Find Pegasus south of the Cassiopeia Constellation and east of the asterism.  This area is known as the “Summer Triangle.” Pegasus’ location is within the NQ4 Quadrant.

When Can You See the Pegasus Constellation? 

Pegasus rides high in Northern Hemisphere skies in the late summer months and continues through the Fall. Star gazers in the Southern Hemisphere have the best viewing from late winter through the Spring.

On August evenings, look for the Great Square of Pegasus as a starting point. Finding a constellation’s brightest stars helps viewers zero in on the correct location. You can see the Great Square with your unaided eyes, but you’ll appreciate using a telescope for more clarity.

Only three of the four star’s in the Great Square actually reside in Pegasus.

  • Markab (Alpha Pegasi) – A-type sub-giant star
  • Scheat (Beta Pegasi) – a red giant
  • Algenib (Gamma Pegasi) – sub giant star

The fourth star, Alperatz (Alpha Andromedae), is actually the constellation Andromeda’s brightest member.

When Can You See the Pegasus Constellation?
Image Credit: JPL, NASA

Another great viewing time for Pegasus is around 9:00 pm local time in the Northern Sky during the month of October. See it between latitudes +90 degrees and -60 degrees. 

Pegasus Constellation Stars, Galaxies, and Dark Sky Objects

The constellation Pegasus is home to many notable celestial objects. From a Milky Way-like spiral galaxy to a quintet of famous galaxies, astronomers find a rich interstellar environment.

Stephan’s Quintet

Stephan’s Quintet lies in the Pegasus Constellation, about 270 million light-years from Earth. These five galaxies gained fame after their appearance in “It’s A Wonderful Life.” They represent the voices of angelic figures, including Clarence, George Bailey’s guardian angel. 

According to the Hubble Space Telescope images, these galaxies are anything but angelic! Two of the galaxies have collided with other deep sky objects, causing space chaos while ejecting stars and gasses into space.

Four galaxies in the Quintet interact on a regular basis. NASA says they are “locked in a cosmic dance of repeated close encounters.” These violent interactions create strings of star clusters and also distort the galaxies’ shapes. 

  • NGC 7319
  • NGC 7318A 
  • NGC 7318B
  • NGC 7317
  • NGC 7320 (non-interacting)

The image below depicts the Quintet from Hubble Legacy Archive data. The dancing partners appear with a yellow tint, while the stand-alone galaxy appears predominantly in blue tones. NGC 7320 is the closest to Earth, at about 40,000 light-years away.

Quintet
Image Credit: NASA, ESA, Hubble Legacy Archive

NGC 7331

NGC 7331 is a big spiral galaxy close in size to the Milky Way. It resides within the Pegasus Constellation, about 50 million light-years distant from Earth. NGC 7331 has vast spiral arms with dark cosmic dust lanes. It contains massive young stars in bluish clusters and active star-forming HII regions. 

There are also older, cooler stars within the central galaxy regions. There is enough cosmic gas and dust in this area to birth about four billion Suns. 

See this galaxy in the upper right of the image below while also noting Stephan’s Quintet in the lower left Quadrant. 

NGC 7331
Image Credit: NASA 

Pegasus’ Brightest Star: Epsilon Pegasi – “Enif”

Epsilon Pegasi is the constellation’s brightest star, with an apparent magnitude varying between 2.37 and 2.45. This orange supergiant marks the spot on the winged horse’s nose. It is visible to your unaided eyes in a dark sky area.

  • Due to its location within the constellation, Epsilon Pegasi gained the name Enif from the Arabic word for “nose.” 
  • Approximately seven times the Sun’s mass
  • It’s about 20 million years old, much younger than the Sun.
  • 4,000 times brighter than the Sun
  • It ranks 82 on the Abrams Planetarium, Michigan State University’s top 100 brightest stars list.
  • About 690 light-years distant

51 Pegasi

Star 51 Pegasi is a Sun-like star about 51 light-years from Earth and estimated at six to eight billion years old. It was the first main-sequence star astronomers found with an orbiting planet. 

Called an exoplanet because it exists outside the Solar System, scientists discovered 51 Pegasi b in 1995. 51 Pegasi b (the planet) orbits 51 Pegasi (the star.) Their discovery changed the way astronomers see the universe.

  • Unofficially named Bellerophon
  • Now officially called Dimidiam

Dimidiam only has about half the mass of Jupiter but twice its size. It orbits its star in 4.2 Earth days. Those two distinctions helped scientists identify a new planet class called Hot Jupiters. These are scorching giant planets that orbit closer to their stars than Mercury.

Conclusion

Early Babylonians noted the Pegasus Constellation during the seventh and sixth centuries B.C.E. Later; it was cataloged as one of 48 constellations in Ptolomy’s Algamest. Pegasus currently is the seventh largest of the 88 known constellations.

Although it contains endless interesting dark sky objects, find this celestial area by locating The Great Square of Pegasus with your naked eye. From there, look for the brightest star of the upside-down winged horse’s nose, Enif. 

Backyard astronomers and movie buffs alike enjoy peering at Stephan’s Quintet. This galaxy group became famous in the holiday movie “It’s a Wonderful Life,” when the five galaxies represented angelic voices from beyond.