As shown on the chart at the top of this post, the Great Square of Pegasus is a great jumping off point for finding the Andromeda galaxy, otherwise known as M31. The Great Square sparkles over your eastern horizon at nightfall, and then travels westward across the sky throughout the night. For some idea of the Great Square’s size, extend your hand an arm’s length from your eye. You’ll see that any two Great Square stars are farther apart than the width of your hand.
As seen from mid-northern latitudes, the Square of Pegasus looks like a baseball diamond whenever it resides in the eastern sky. Imagine the farthest star to the left – Alpheratz – as the third-base star. An imaginary line drawn from the first-base star through Alpheratz points in the general direction of the Andromeda galaxy.
If it’s dark enough, you’ll see two streamers of stars flying to the north (or left) of the star Alpheratz. To me, this grouping of stars looks like a bugle or a cornucopia. Along the bottom streamer, star-hop from Alpheratz to the star Mirach. Draw an imagainary line from Mirach through the upper streamer star (Mu Andromedae), and go twice the distance. You’ve just located the Andromeda galaxy!
If you can’t see this fuzzy patch of light with the unaided eye, maybe your sky isn’t dark enough. Try binoculars! If you can find the Great Square of Pegasus, then you can star-hop to the Andromeda galaxy.
By the way, if you’re up before dawn tomorrow – on Thursday, September 26 – let the moon guide your eye to the bright stars of the Winter Circle.