Fall Constellation Spotlight: Pegasus
October 4, 2024
Night has become noticeably longer, with Fall in full swing in the Northern Hemisphere. It’s the perfect time to focus on Pegasus, the white-winged stallion. Let’s explore the constellation’s history, star patterns, and the prominent celestial objects in or around its boundaries.
Pegasus is the seventh largest of the 88 constellations, sharing a border with Andromeda, Cygnus, and Pisces. The Greek astronomer Ptolemy cataloged Pegasus in the second century. There are a few myths about Pegasus’ origins. According to classic Greek mythology, Pegasus was born when the hero Perseus cut off the head of the gorgon Medusa, who had venomous snakes for hair. Perseus used Medusa’s ugly head to turn the sea monster Cetus into stone before it could feast upon the beautiful Princess Andromeda, who was chained to a rock. When Medusa’s blood dripped and mixed into the foaming seawater, Pegasus emerged as an elegant white-winged stallion with a golden mane who could fly quickly and gracefully.
Asterism
|
|
The Great Square of Pegasus is a prominent asterism high in the sky during October and November evenings that is easily recognizable to stargazers. It forms Pegasus’ body and comprises four medium-bright stars: Alpheratz (Alpha Andromedae), Algenib (Gamma Pegasi), Markab (Alpha Pegasi), and Scheat (Beta Pegasi). Alpha Andromedae, known as Alpheratz, is a tight binary star system. Although it is officially one of the brighter stars of Andromeda at magnitude +2.06, it marks the northeastern corner square of Pegasus. Alpheratz is derived from an Arabic phrase meaning the horse’s navel, but it is now commonly called “the horse’s shoulder.” |
Notable Star
|
|
In addition to the four stars of the Great Square, there is another noteworthy star in Pegasus. Enif (Epsilon Pegasi), an orange supergiant star with an apparent magnitude of +2.39, is the brightest star in Pegasus. In Arabic, enif means “the nose” or the “muzzle” of the mythical winged horse. It lies approximately 670 light years from Earth and has a total luminosity of 6,700 suns. |
Deep-Sky Objects
|
|
Messier 15 is a well-known globular cluster in Pegasus. Jean-Dominique Maraldi discovered it in 1746, and Charles Messier included it in his catalog in 1764. With an apparent magnitude of +6.2, M15 appears as a fuzzy star in binoculars or small telescopes. In larger aperture telescopes, especially when viewed from dark skies, this cluster comes alive with a blazing center and arms of stars radiating away from its core. M15 lies approximately 33,600 light years from Earth and is one of the Milky Way galaxy’s most densely packed globular clusters. Interestingly, M15 is the first globular cluster in which a planetary nebula, Pease 1, was first identified in 1928. |
|
|
Stephan's Quintet is a famous group of five faint galaxies showing gravitational interactions. Located in the constellation of Pegasus, it was discovered in 1878 by French astronomer Édouard Stephan in 1877 at the Marseille Observatory. Located roughly 290 million light-years away, Stephan's Quintet is invisible in most backyard telescopes from suburban skies. Observing this galaxy group will require a telescope with 11 inches or larger apertures and very dark skies to resolve its members. |
|
 |
NGC 7331 is a beautiful, unbarred spiral galaxy about 49 million light-years from Earth. Sir William Herschel discovered it in 1784. Some astronomers refer to NGC 7331 as the Milky Way’s “twin” due to its comparable size and structure. Surrounding this galaxy are four smaller galaxies, known as the “fleas,” which are much further away. The entire grouping of galaxies has earned the nickname the “Deer Lick Group.” NGC 7331 has an apparent magnitude of +10.4—within reach of most telescopes from a dark-sky site. Interestingly, this galaxy was one of 18 key galaxies chosen to calibrate the galactic distance scale, using the Hubble Space Telescope to obtain an accurate distance via Cepheid variable observations. |
|
 |
The Propeller Galaxy (NGC 7479), also known as the Superman Galaxy, is a barred spiral galaxy about 105 million light-years away. Discovered by William Herschel in 1784, it features a prominent bar structure with spiral arms that appear in opposite directions, like the letter “S.” It resides close to the celestial equator and is visible from both hemispheres at certain times of the year. The Propeller Galaxy has an apparent magnitude of +11.6 and is visible in a telescope with at least 6 inches of aperture or larger in dark skies. |
Pegasus has remarkable features and is known for its numerous galaxies and celestial objects. In 1995, astronomers discovered an exoplanet orbiting one of the constellation’s stars, 51 Pegasi. Later, astronomers discovered exoplanets orbiting two other stars in Pegasus. One of the stars, HR 8799, is at the center of a system of at least four massive planets!
Fall is a transitional season that lacks the brilliant stars and distinct constellations of Winter, Spring, and Summer. That’s because, during Fall, we look out of the plane of our galaxy and away from many Milky Way objects. Even so, the exciting celestial objects in Pegasus make excellent targets to observe when conditions are favorable. Enjoy the Fall sky with your family and friends before the cold sets in.
Clear skies and happy observing!
