This famous four-star asterism marks the body of Pegasus the Winged horse and can help point the way to many fainter objects.
- The article describes the observation of the Great Square of Pegasus, an asterism easily visible throughout the night due to its brightness.
- The asterism comprises four stars: Gamma Pegasi, Markab (Alpha Peg), Scheat (Beta Peg), and Alpheratz (Andromeda’s Alpha star), with approximate magnitudes and relative positions described.
- The observation is best performed an hour after sunset, with the square rising in the east and traversing the sky overnight.
- Despite the waxing gibbous moon, the article suggests learning the Great Square as a reference point for finding fainter celestial objects under darker skies.
With a waxing Moon lighting the sky for most of the night, we’re focusing on brighter stars this evening. Our target for tonight is a famous asterism that is currently visible all night long. You can catch it already above the horizon in the east an hour after the Sun disappears, then follow its progress as it arcs through the sky overnight.
Look east an hour after sunset and you’ll spot a large diamond of stars — this is the Great Square of Pegasus, which depicts the body of the Winged Horse. It is bounded by four stars; lowest early in the evening is magnitude 2.8 Gamma Pegasi. Moving counterclockwise, some 16.5° to its upper right (west) is magnitude 2.5 Markab (Alpha Peg). The next star is Scheat (Beta Peg), which shines at magnitude 2.5 and sits roughly 13° north (to the upper left) of Markab. As the Great Square is Rising, Scheat appears at the top of the diamond, directly above Gamma.
Finishing off the Great Square is a star that isn’t actually in Pegasus — it’s Alpheratz, Andromeda’s magnitude 2.1 alpha star, which lies just over 14° east (to the lower left) of Scheat.
Although the sky is bright with moonlight tonight, taking the time to learn the Great Square will help guide your way to many fainter objects when the nights grow darker again.
Sunrise: 6:30 A.M.
Sunset: 7:28 P.M.
Moonrise: 5:27 P.M.
Moonset: 1:34 A.M.
Moon Phase: Waxing gibbous (82%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 12 P.M. local time from the same location.
For a look ahead at more upcoming sky events, check out our full Sky This Week column.