Pegasus is one of the largest and most easily recognizable star patterns in the night sky, officially named after the mythical winged horse. Known for the distinct square shape that forms its body, Pegasus covers a vast area of the celestial sphere. It is one of the 88 modern constellations recognized by the International Astronomical Union, and its size makes it the seventh largest overall. Pegasus resides primarily in the Northern Celestial Hemisphere.
The Constellation’s Celestial Location
The placement of Pegasus is confirmed by its celestial coordinates, specifically its declination, which is the astronomical equivalent of latitude on Earth. The constellation’s boundaries span a declination range from approximately +2.33 degrees to +36.61 degrees. Since the celestial equator is marked at 0 degrees, this positive range indicates that the majority of the constellation lies north of this dividing line, establishing its northern designation.
This northern position makes the constellation highly visible to observers across the mid-Northern latitudes, where it can be seen high overhead during its peak viewing season. Because a portion of the constellation dips slightly below the celestial equator, people in the Southern Hemisphere can see part of Pegasus, appearing low on the northern horizon. However, for observers farther south than about 60 degrees latitude, the constellation is extremely difficult to spot or entirely invisible.
Finding the Great Square
The most effective way to locate Pegasus is by finding its most prominent asterism, the Great Square of Pegasus, which outlines the winged horse’s torso. This large square shape is instantly recognizable, though it is not a perfect geometric shape. Its four bright corner stars create a distinct quadrilateral that dominates the autumn sky for Northern Hemisphere viewers.
The best time for viewing the Great Square is during the evening hours of autumn, particularly in October, when it rises high in the eastern sky after dark. The asterism is substantial, spanning about 15 degrees across the sky, roughly the width of a clenched fist held at arm’s length.
The Great Square serves as a crucial navigational landmark. For example, the star at its northeastern corner, Alpheratz, leads into the neighboring constellation Andromeda. The star at the western side of the square can also be used to “star-hop” south to locate the bright star Fomalhaut.
Important Stars and Deep Sky Features
The Great Square is formed by three stars belonging to Pegasus—Markab, Scheat, and Algenib—and the star Alpheratz (which belongs to Andromeda). Markab (Alpha Pegasi), a blue-white giant, forms the southwest corner. Scheat (Beta Pegasi), a red giant, is at the northwest corner, and Algenib (Gamma Pegasi), a hot, blue-white star, completes the triad at the southeast corner.
The constellation’s brightest star is Enif (Epsilon Pegasi), an orange supergiant that marks the horse’s muzzle, positioned outside the Great Square. Pegasus is also famous for containing 51 Pegasi, a Sun-like star that made history in 1995 by hosting the first discovered exoplanet of its type, 51 Pegasi b.
For deep-sky observers, the constellation hosts the ancient globular cluster M15, a dense collection of over 100,000 stars. Another significant object is the spiral galaxy NGC 7331, often called a twin of the Milky Way due to its similar structure.