The constellation Andromeda the Chained Lady

Star chart of constellation Andromeda at bottom right and Cassiopeia upper left with labels and galaxy.
The W-shaped constellation Cassiopeia points to the stars of the constellation Andromeda, with the spiral galaxy inside the border of Andromeda. Chart via Chelynne Campion/ EarthSky.

The constellation Andromeda is named for the daughter of Queen Cassiopeia and King Cepheus of Greek mythology. Andromeda has the nickname of the Chained Lady because her parents chained her up and offered her as a sacrifice to appease the sea monster Cetus. In the story, she is saved by Perseus and eventually becomes his queen. All these mythological characters are now visible as constellations in the night sky.

Andromeda and surrounding constellations.
View larger. | Andromeda the Chained Lady lies near her parents, Queen Cassiopeia and King Cepheus. She also contributes one star to the Great Square of Pegasus. Image via Stellarium. Used with permission.

How to find the constellation Andromeda

Andromeda is easy to find because of the company it keeps. The W-shaped constellation of Cassiopeia points toward Andromeda. Andromeda is also next to the Great Square of Pegasus. In fact, one of the stars of the Great Square actually belongs to Andromeda.

November is an excellent month to try to spot Andromeda the Chained Lady. Look east after it gets dark to find the constellation already high above the horizon. Andromeda favors viewers in the Northern Hemisphere; it is not visible to those south of 40 degrees south latitude. The constellation is the 19th largest, in size, of the 88 constellations. The finder charts above can guide you to it.

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Stars of the constellation Andromeda

The brightest star in the Great Square of Pegasus actually belongs to Andromeda: the magnitude 2.06 star Alpheratz. Alpheratz lies 97 light-years away. Another magnitude 2.06 star, Mirach, lies to the upper left of Alpheratz. Mirach lies 197 light-years away and is the closest bright star to the Andromeda Galaxy. The third brightest star in Andromeda is magnitude 2.26 Almach, to the upper left of Mirach. Almach lies 355 light-years away.

Star chart with stars in black on white and red oval for galaxies.
A star map of the constellation Andromeda showing the locations of the Andromeda Galaxy (M31) and the Triangulum Galaxy (M33). Image via IAU/ Sky & Telescope/ Wikimedia Commons/ Attribution 3.0 Unported (CC BY 3.0).
Andromeda galaxy shown as a large glowing oblong galaxy in the upper right corner, reddish star at center, hazy patch bottom left.
View at EarthSky Community Photos. | Soumyadeep Mukherjee in Kolkata, India, captured this photo of the constellation Andromeda with the galaxy and red star Mirach on September 30, 2021. He wrote: “The image contains at least 4 observable galaxies: M31 (Andromeda Galaxy) at the top-right corner, M33 (Triangulum Galaxy) at the bottom-left corner, M32 and M110 (both near the Andromeda Galaxy). Along with that, we also have an open cluster NGC 752/Caldwell 28 at the top-left corner. At the middle of the image, it is the red giant Mirach!” Thank you, Soumyadeep!

Finding the Andromeda Galaxy with Cassiopeia

Although M31, the Andromeda Galaxy, is centrally located in the constellation Andromeda, it is actually easier to find by using the stars of Cassiopeia. The magnitude 3.5 galaxy can be seen as a hazy patch in a dark sky, but most people will need binoculars or a telescope to find the wide misty patch.

Andromeda stretches about three degrees across and one degree wide. It lies at a distance of approximately 2.5 million light-years from Earth, which means that as we view the light from Andromeda, we are seeing it as it was 2.5 million years ago.

To find the Andromeda Galaxy, look for the W shape of Cassiopeia. With the two V shapes that make up the W, use the V shape on the right. Imagine the V as an arrow, pointing into the constellation Andromeda. From the tip of the arrow star to the spiral galaxy, the angular distance is a little over 15 degrees. (Hold your hand at arm’s length and use your index finger and pinky spread apart to measure 15 degrees on the sky’s dome.) The arrow of Cassiopeia does not point precisely to Andromeda: You will have to look a bit to the right to find the galaxy M31.

Animation of a star chart to show how to find Andromeda Galaxy from the constellation Cassipeia.
Most people use the M- or W-shaped constellation Cassiopeia to find the Andromeda galaxy. See how the V shape points to the galaxy? Chart via Used with permission.

Finding Andromeda Galaxy with Andromeda

To use a star from Andromeda to find the galaxy, start with the star that is connected to the Great Square of Pegasus. Then look left and find three stars leading away from it: a 3rd magnitude star (Delta Andromedae), Mirach and Almach. Focus on Mirach, and then look above Mirach. There are two stars in a line above it, the top one dimmer than the bottom. If you can see the highest star without optical aid, look just to its right for a slightly lighter patch of sky. Put your binoculars or a telescope on it to confirm that you’ve found Andromeda.

Animation of a star chart to show how to find Andromeda Galaxy from the constellation Andromeda.
Find the Andromeda Galaxy by star-hopping from the Great Square of Pegasus. Chart via Used with permission.

Observing M31, the Andromeda Galaxy

M31, at magnitude 3.5, should be easy to see once you have it located in your binoculars or telescope. The grayish patch should show an oval shape, characteristic of spiral galaxies. Two other Messier objects are within your field of view when you are looking at Andromeda. M32 and M110 and elliptical galaxies that are companions to the large Andromeda Galaxy. They also lie 2.5 million light-years away. M32 is magnitude 8.1 and is closest to the galaxy, appearing to lie on the larger spiral’s edge. M110 is magnitude 8.5 and is a bit farther away from the large spiral.

Very oblique view of fuzzy, yellowish spiral with glowing white center, dark lanes and foreground stars.
View at EarthSky Community Photos. | Paul Wilson in Paso Robles, California, captured this telescopic view of the Andromeda galaxy on August 18, 2023. Paul wrote: “Andromeda galaxy, known as Messier 31, in a collection of subframes taken over 4 nights from a Bortle 4 to 5 area.” Thank you, Paul!

Bottom line: The constellation Andromeda the Chained Lady is most famous for containing the closest large spiral galaxy to the Milky Way.

November 12, 2023

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