I'm going to give you a key. It's called the Square of Pegasus. Once you learn to recognize this broad, boxy figure you'll find it can point you to most anywhere in the autumn sky. It's a big square or diamond — take your pick — outlined by four stars with magnitudes between 2.0 and 2.8, equal to or a bit fainter than the stars in the Big Dipper. They're named Scheat, Alpheratz, Markab and Algenib and enclose a mostly empty space.

That's part of the reason the Square is so easy to find. It's a whole lot of nothing — with neat borders. Of course, there's not really nothing there. From a dark sky, at least a dozen faint stars twinkle from within this box.

Each star in the corners of the Great Square has an Arabic-based name. Alpheratz is the word for "horse's navel;" Scheat means "shin;" Algenib the "flank" and Markab the "horse's shoulder." 
Contributed / Bob King
Each star in the corners of the Great Square has an Arabic-based name. Alpheratz is the word for "horse's navel;" Scheat means "shin;" Algenib the "flank" and Markab the "horse's shoulder." Contributed / Bob King

The Great Square spans about 15° on a side, equal to one-and-a-half fists, and stands halfway up in the southeastern sky around 8 p.m. local daylight time in mid-October. It forms the brightest part of a much larger figure, Pegasus the Flying Horse, so it's not actually a constellation but rather an asterism. Poking out from the upper right of the square from Scheat (SHEE-at) are the horse's legs, while its long neck and head extend south and west from Markab at the lower right corner.

The Great Square and several of the season's fainter constellations dominate the south-southeastern sky on October nights. 
Contributed / Stellarium
The Great Square and several of the season's fainter constellations dominate the south-southeastern sky on October nights. Contributed / Stellarium

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What looks like a tail sticking out to the left of Alpheratz (AL-fer-ratz) is actually a separate constellation — Andromeda the Princess. Although it's perfectly at home in Pegasus, Alpheratz instead belongs to Andromeda. Starting here, you can slide east (left) and pick out two, curved strings of stars that outline the figure of a princess. That may well be, but they'll always remind me more of a an old rabbit-ears TV antenna.

The Square will point you to several fall constellations simply by extending the lines across and through its sides. Distances between the figure and the labeled stars are shown in degrees. One fist held at arm's length spans about 10°. Contributed / Stellarium with additions by Bob King
The Square will point you to several fall constellations simply by extending the lines across and through its sides. Distances between the figure and the labeled stars are shown in degrees. One fist held at arm's length spans about 10°. Contributed / Stellarium with additions by Bob King

Next, we'll use the sides of the Great Square as arrows to point to several bright stars. These stars will become stepping stones you can use to connect nearby fainter stars into the outlines of their respective constellations. Shoot a line from Algenib through Scheat, and it will take you straight to Deneb, the tail of Cygnus the Swan. A line extended west from Algenib and Markab will send you to Altair in Aquila the Eagle. In a similar manner, you can branch out to Diphda in Cetus the Sea Monster, Fomalhaut in Piscis Austrinus the Southern Fish and Hamal, Aries' brightest star.

With its many uses the Great Square is truly the fall night sky's pocketknife. It represents the body of Pegasus the Winged Horse, which flies upside-down as viewed from mid-northern latitudes. To see it fly right side up you'll have to take a trip to the equator or further south, where the celestial stallion wings across the northern sky.

This Roman mosaic from the 2nd to 3rd century depicts Bellerophon riding Pegasus while slaying the Chimera. 
Contributed / Public domain
This Roman mosaic from the 2nd to 3rd century depicts Bellerophon riding Pegasus while slaying the Chimera. Contributed / Public domain

Pegasus comes to us like so many constellations through Greek mythology. The horse sprang to life from the body of Medusa after Perseus the Hero cut off her head. Later, he became the steed of the hero Bellerophon, who was charged with the mission of killing Chimera, a fire-breathing monster.

After that success and others, Bellerophon attempted to fly to Mt. Olympus and join the gods, but before he could, he fell back to Earth. Pegasus completed the journey and worked for Zeus, toting the chief's lightning bolts and thunder. To honor the flying stallion Zeus placed Pegasus in the sky as one of the constellations.

And the horse has kept busy since then working as a full-time star guide.

"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.