Pegasus: The Winged Horse and the Great Square

Pegasus is one of the largest constellations in the autumn sky, dominated by the Great Square of Pegasus, a vast asterism that serves as the primary signpost for navigating the October and November heavens. The Great Square's nearly empty interior and distinctive shape make it one of the most useful landmarks in the sky. Find it tonight with StarGlobe.

How to Find Pegasus

Look high in the south during autumn evenings (for Northern Hemisphere observers) and search for a large square formed by four second-magnitude stars. The Great Square is roughly 15 degrees on a side, slightly larger than your fist at arm's length. Its sides are oriented roughly along the cardinal directions.

The Great Square is remarkably empty of bright stars. Under dark skies, you might count a handful of faint stars inside it, but from suburban locations, the interior appears completely blank. This emptiness actually helps identify the pattern.

Technically, only three of the four corner stars belong to Pegasus. The northeastern corner, Alpheratz, is formally assigned to Andromeda. The Pegasus stars are Markab (Alpha), Scheat (Beta), and Algenib (Gamma). Lines of stars extending from the western side of the Square form the horse's neck and head.

The Stars of Pegasus

Enif (Epsilon Pegasi) is actually the brightest star in the constellation at magnitude 2.4, located on the horse's muzzle well to the west of the Great Square. It is an orange supergiant about 670 light-years away and has been observed to flare unpredictably, briefly brightening by several magnitudes on rare occasions.

Scheat (Beta Pegasi), at the northwestern corner of the Square, is a red giant that varies between magnitudes 2.4 and 2.8. Its warm reddish color is visible to the naked eye and contrasts with the whiter corner stars. Markab (Alpha Pegasi), at the southwestern corner, is a blue-white subgiant at a steady magnitude 2.5.

Algenib (Gamma Pegasi), at the southeastern corner, is a hot blue-white star that pulsates slightly in brightness. It is a Beta Cephei variable, changing brightness by a small amount over a period of about 3.6 hours.

Deep Sky Objects

M15 is one of the finest globular clusters in the sky, located about 4 degrees northwest of Enif. At magnitude 6.2, it is visible in binoculars and resolves beautifully in telescopes. M15 is about 33,600 light-years away and is one of the most densely packed globular clusters known, having undergone core collapse. It also contains a planetary nebula, Pease 1, one of only four known planetary nebulae within globular clusters.

NGC 7331 is a spiral galaxy often called the Milky Way's twin because of its similar size and structure. It lies about 40 million light-years away and is bright enough for small telescopes. Nearby, the Stephan's Quintet (NGC 7317-7320) is a famous group of five galaxies, four of which are physically interacting at a distance of about 300 million light-years. Stephan's Quintet was beautifully imaged by the James Webb Space Telescope, becoming one of its iconic early images.

The Pegasus Dwarf, a small satellite galaxy of the Andromeda Galaxy, lies within the constellation's boundaries.

Mythology and Cultural Heritage

In Greek mythology, Pegasus was a winged horse born from the blood of Medusa when Perseus beheaded her. The horse flew to Mount Olympus, where he was tamed by the hero Bellerophon, who rode Pegasus to slay the Chimera. When Bellerophon attempted to ride Pegasus to Olympus, he was thrown off, but the horse continued and was placed among the stars by Zeus.

The constellation depicts only the front half of the horse, appearing upside down in the sky for Northern Hemisphere observers. The wings would extend from the area of the Great Square. The connection between Pegasus and the nearby mythological constellations of Perseus, Andromeda, Cassiopeia, and Cepheus creates one of the richest story arcs in the sky.

Best Time to Observe

Pegasus is best observed during October and November evenings, when the Great Square passes nearly overhead for mid-northern latitude observers. The constellation is visible from August through January. From the Southern Hemisphere, Pegasus appears in the northern sky during spring months but is lower and less impressive.

Neighboring Constellations

Andromeda extends from the northeastern corner of the Great Square. Pisces wraps around the southern and eastern sides. Aquarius lies to the south, and Cygnus sits to the west. Lacerta fills the space between Pegasus and Cassiopeia. Use the Great Square as your starting point and explore the autumn sky with StarGlobe.

Quick Facts

Pegasus covers 1,121 square degrees, ranking 7th in size. It contains one Messier object (M15). Enif shines at magnitude 2.4. The constellation's right ascension ranges from about 21h 08m to 0h 14m, and its declination spans from about +2 to +36 degrees.