Pegasus the Flying Horse, and the best sky story ever

Pegasus the Flying Horse

Pegasus the Flying Horse rises in the east on autumn evenings in the Northern Hemisphere (spring evenings in the Southern Hemisphere). It dominates the sky with its giant square asterism, fittingly called the Great Square. In mythology, Pegasus figured into the greatest – surely the most elaborate – of all sky myths. This one is from ancient Greece some 3,000 years ago. According to the myth, Pegasus was the flying horse ridden by Perseus the Hero, as he swooped in to save Princess Andromeda from a sea monster. There’s more to the story, which you’ll find in the video at the top of this page.

Today, we see Pegasus as the 7th-largest of the 88 official constellations. And Pegasus is easy to find. On fall evenings in the Northern Hemisphere, this constellation climbs above the eastern horizon, reaching a spot nearly overhead by late fall.

Its asterism – the Great Square of Pegasus – is huge. The square alone is 20 degrees wide from top to bottom. That’s the span of two fist-widths held at arm’s length.

The 2024 lunar calendars are here! Best Christmas gifts in the universe! Check ’em out here.

Sky chart with numerous labeled stars and lines between them making a large square with legs.
On autumn evenings in the Northern Hemisphere – spring evenings in the Southern Hemisphere – Pegasus the Flying Horse is ascending in the east in the evening hours. You’ll most easily notice the giant, square-shaped asterism within Pegasus, called the Great Square.

Stars of Pegasus

As it rises in the evening, the star in the Great Square closest to the horizon is Algenib, with a magnitude of 2.8. It lies 333 light-years away. The star on the opposite corner of the square from Algenib is Scheat, a magnitude 2.4 star lying 199 light-years away. The star to the south in the square is Markab, a magnitude 2.5 star at a distance of 140 light-years. And the final star in the square is Alpheratz. Technically, Alpheratz lies just across the border of Pegasus and is actually a member of the constellation Andromeda. Alpheratz is the brightest of the four stars at magnitude 2.1 and lies 97 light-years away.

The Great Square marks the body of the flying horse. Trails leading off the west side of the square mark the front legs and head of Pegasus. Extending out from Markab, two stars at magnitude 3.4 and 3.5, Homam and Biham, lead the way to the head star, magnitude 2.4 Enif. This star will be helpful in finding the globular cluster M15.

Find the forelegs of Pegasus off of Scheat. Five degrees west of Scheat is magnitude 3.0 Matar. As the brightest leg star in Pegasus, it’s helpful in finding a couple of notable galaxies.

Star chart with pictures of Pegasus the Flying Horse and neighboring constellations.
Pegasus the Flying Horse is a giant constellation that rises in the east on October evenings. Image via Stellarium. Used with permission.

The asterism of the Great Square

The Great Square of Pegasus can look like a huge diamond. Think of it as a giant baseball diamond rising during playoffs month in the east after dark. Asterisms, such as the Great Square, are groups of stars that aren’t labeled as constellations but are easy to recognize.

Night sky photo with lines between stars and a man pointing up at the constellation.
View at EarthSky Community Photos. | Prateek Pandey in Bhopal, India, captured this photo of Pegasus on October 8, 2021. He wrote: “Pegasus is named after the winged horse in Greek mythology. Curiously, the constellation Pegasus only represents the top half of the horse. In some depictions, the horse is shown rising out of the water. Viewed best in autumn, turn your eyes to the east as the night falls, and see the winged horse rising high up in the sky.” Thank you, Prateek!

Using Pegasus to find the Andromeda Galaxy

Pegasus is close to the constellation Andromeda, so it’s useful for star-hopping to the Andromeda galaxy. You’ll need a dark-sky site to track down Andromeda without optical aid. It’s much easier to spot with binoculars or a telescope. Follow this link for more information on how to use Pegasus to find Andromeda.

Star chart: Lines showing constellations with large square and arrow pointing to galaxy symbol.
Find the Andromeda Galaxy (M31) by star-hopping from the Great Square of Pegasus. Chart via Chelynne Campion/ EarthSky.

Stephan’s Quintet

Pegasus is home to many galaxy clusters. The most famous is probably Stephan’s Quintet, a favorite target among astrophotographers. This tight gathering of five galaxies has a magnitude of 13.6. The largest and brightest, NGC 7320, has a small redshift compared to the other four, revealing that it is probably not a physical member of the group and just a line-of-sight coincidence.

Fun fact: In the 1946 movie It’s a Wonderful Life, angels in heaven discussing George Bailey are depicted as the galaxies in Stephan’s Quintet.

A cluster of galaxies including large colorful spirals and two galaxies merging.
This image of Stephan’s Quintet is from 2009, courtesy of the Hubble Space Telescope. Image via Wikimedia Commons (public domain)/ NASA/ ESA/ and the Hubble SM4 ERO Team.

Other galaxies in Pegasus the Flying Horse

Three other notable galaxy clusters lie in Pegasus. The brightest is magnitude 9.5 and is just half a degree from Stephan’s Quintet. The cluster has the curious name Deer Lick Group. Follow Scheat to Matar and then about 4.5 degrees farther and slightly north of the direction you were heading. This will bring you to the Deer Lick Group, NGC 7331. Here you’ll find one large spiral galaxy and a spattering of smaller ones.

Large, oblique spiral galaxy and some smaller spiral and elliptical galaxies nearby in star field.
The Deer Lick Group contains one large spiral galaxy and other smaller galaxies. It lies in the constellation Pegasus. Image via W4sm astro/ Wikimedia Commons (CC BY-SA 4.0).

The Pegasus I Cluster lies on the southern edge of the constellation not far from the circlet of Pisces. At a distance of 8 degrees from Markab on the sky’s dome, the Pegasus I Cluster is a magnitude 11.1 grouping. The galaxy cluster requires a large telescope to see or a long-exposure photograph, but it reveals a beautiful and striking number of galaxies.

The Pegasus II Cluster lies back within the square of Pegasus. Halfway between Alpheratz and Scheat, it lies just inside the border of a line that would be drawn connecting these two stars. A bit dimmer at magnitude 12.6, the Pegasus II Cluster (NGC 7720) is a powerful radio source, the target of much scientific study.

Globular Cluster M15 in Pegasus the Flying Horse

One other deep-sky object of note in Pegasus is the globular cluster M15. You can find M15 easily using the head and neck stars of Pegasus. Start with the star Markab and go to the two dimmer stars that mark the neck. From the last star of the neck (Biham) to the brighter head star Enif, continue a line straight out for a little more than 4 degrees. Here you will find the magnitude 6.4 globular cluster M15. It lies about 33,600 light-years away and will show up nicely in a pair of binoculars.

Countless colorful points of light clustered together with a bright center and spilling outward into a starfield.
You can find the globular cluster M15 in the constellation Pegasus. It shines at magnitude 6.4. Image via Mount Lemmon SkyCenter Schulman Telescope/ Adam Block/ Wikimedia Commons (CC BY-SA 4.0).

First exoplanet around a sun-like star

Astronomers discovered the first exoplanet orbiting a sun-like star in the constellation Pegasus. They named the planet 51 Pegasi b after the star it orbits. Didier Queloz and Michel Mayor discovered the planet in 1995 and received the Nobel Prize in Physics for their discovery in 2019.

Yellow, brown, and tan striped planet with distant yellowish-white star.
Artist’s concept of the hot Jupiter exoplanet 51 Pegasi b. The first planet discovered around a sun-like star, 51 Pegasi b lies about 50 light-years from Earth in the constellation Pegasus the Flying Horse. Image via ESO/ M. Kornmesser/ Nick Risinger/ Wikimedia Commons (CC BY 4.0).

Bottom line: Pegasus the Flying Horse is a giant constellation that dominates autumn skies in the Northern Hemisphere (spring skies in the Southern Hemisphere). The constellation contains a famous asterism called the Great Square.

November 12, 2023

Like what you read?
Subscribe and receive daily news delivered to your inbox.

Your email address will only be used for EarthSky content. Privacy Policy
Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.

More from 

Kelly Kizer Whitt

View All