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Great Square points to Andromeda galaxy

The Great Square of Pegasus looks like a … well … a big square. Four medium-bright stars mark its corners. But if you can think of it instead as a baseball diamond, you can use the Square to find the famous Andromeda galaxy.

It’s the large spiral galaxy next door to our Milky Way and one of the most distant objects visible to the eye alone. Look at the Square on our chart at top. Now imagine the farthest star to the left – Alpheratz – as the third-base star. A line drawn from the opposite first-base star through Alpheratz points in the general direction of the Andromeda galaxy.

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.

At mid-northern latitudes, the Great Square of Pegasus sparkles over your eastern horizon at about 8 or 9 p.m. in late August and early September. That’s 8 or 9 p.m. local time. Some two weeks from now – in September – the Square will return to the same place in the sky about an hour earlier.

Want to see the Great Square of Pegasus from your specific location on the globe, or at a different time of night or different time of year? Try Stellarium.

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Dense star field above treetops, showing small elongated bright smudge of light with brighter center.
View larger. | The Andromeda galaxy (right side of photo) as seen by Ted Van at a Montana campsite on an August evening.

Star-hopping to the Andromeda galaxy

Now let’s get more specific. If it’s dark enough, you’ll see two streamers of stars flying to the north (or left) of the star Alpheratz on August and September evenings. You might see these two streamers in the pattern of a bugle or a cornucopia.

That pattern isn’t part of Pegasus. It’s the constellation Andromeda the Princess. Along the bottom streamer, star-hop from Alpheratz to the star Mirach. Draw a line from Mirach through the upper streamer star – which is called Mu Andromedae – and go about the same distance again. You’ve just located the Andromeda galaxy!

Read more: Cassiopeia the Queen also points to the Andromeda galaxy

The Andromeda galaxy looks like a large fuzzy patch in a dark sky. If you can’t see this fuzzy patch of light with the unaided eye, maybe your sky isn’t dark enough. Try binoculars! Don’t worry if you miss it tonight, for the Andromeda galaxy will be in the evening sky from now until spring.

Oblique view of flat, glowing spiral with bright center and two nearby small smudges of light.
The Andromeda galaxy and 2 satellite galaxies as seen through a powerful telescope. To the eye, the galaxy looks like a fuzzy patch. It’s an island of stars in space, much like our Milky Way. Image via NOAO.

Bottom line: The Andromeda galaxy can be seen somewhere in our sky for much of every year. Every August, it’s ascending in the sky during the evening hours. This post explains how to use the Great Square of Pegasus to find the Andromeda galaxy.

Read more: Mirach is guide star to 3 galaxies

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August 26, 2020
Sky Archive

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