How to Find the Andromeda Galaxy, 2.5 Million Light-Years Away

November and December are good months to look for the constellation Andromeda and the Andromeda Galaxy inside it, according to EarthSky. After dark, look east, where the constellation already sits high above the horizon. The galaxy, known as M31, is a hazy patch of light that EarthSky says most people will need binoculars or a telescope to see.

EarthSky describes Andromeda as easy to find because of its neighbors: the W-shaped constellation Cassiopeia and the Great Square of Pegasus both point the way.

Where Andromeda sits in the sky

Andromeda is the 19th largest of the 88 constellations, EarthSky reports. It favors viewers in the Northern Hemisphere and cannot be seen from places south of 40 degrees south latitude.

In Greek mythology, Andromeda was the daughter of Queen Cassiopeia and King Cepheus. Her parents chained her up as a sacrifice to appease the sea monster Cetus, which earned her the nickname the Chained Lady. In the story, Perseus rescues her and she eventually becomes his queen. EarthSky notes that all of these characters now appear as constellations.

The brightest stars to use as landmarks

Three stars in Andromeda stand out, according to EarthSky:

• Alpheratz: magnitude 2.06, 97 light-years away. It is the brightest star in the Great Square of Pegasus, yet it belongs to Andromeda.
• Mirach: also magnitude 2.06, 197 light-years away, to the upper left of Alpheratz. It is the closest bright star to the Andromeda Galaxy.
• Almach: magnitude 2.26, 355 light-years away, to the upper left of Mirach.

Two ways to find the galaxy

From Cassiopeia. Find the W shape and use the V on the right. Picture that V as an arrow pointing into Andromeda. From the tip of the arrow to the galaxy is a little over 15 degrees, which EarthSky says you can estimate by spreading your index finger and pinky at arm’s length. The arrow does not point exactly at the galaxy, so look a bit to the right.

From the Great Square of Pegasus. Start at Alpheratz and look left to find three stars leading away from it: Delta Andromedae, a 3rd-magnitude star, then Mirach and Almach. Focus on Mirach and look above it, where two stars sit in a line, the upper one dimmer. If you can see that highest star without help, look just to its right for a slightly lighter patch of sky. Then use binoculars or a telescope to confirm you have found the galaxy.

What you will see through binoculars

M31 has a magnitude of 3.5. In a dark sky it shows as a wide, misty patch. Through binoculars or a telescope, EarthSky says, it should appear as a grayish oval, a shape typical of spiral galaxies.

Two smaller galaxies share the field of view. M32, at magnitude 8.1, is the closest to the big spiral and appears to sit on its edge. M110, at magnitude 8.5, lies a bit farther out. Both are elliptical galaxies and companions to M31, and both are also 2.5 million light-years away.

Why it matters for skywatchers

EarthSky calls Andromeda the home of the closest large spiral galaxy to the Milky Way. For anyone with binoculars and a dark sky, that makes it a rare chance to look at another galaxy without specialized equipment.

The distance adds to the appeal. M31 is about 2.5 million light-years away, so the light reaching your eyes left it 2.5 million years ago. Observers in the Northern Hemisphere can try the search this month and next, while the constellation rides high in the east after dark. Those south of 40 degrees south latitude will not be able to see it.

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Around Prague, based on reporting by EarthSky