Andromeda: The Chained Princess and Her Galaxy

Andromeda is a constellation of the autumn sky best known for hosting the Andromeda Galaxy (M31), the most distant object visible to the naked eye and our nearest large galactic neighbor. The constellation itself forms an elegant chain of stars stretching from the Great Square of Pegasus, linking some of the most storied constellations in the sky. Locate it with StarGlobe.

How to Find Andromeda

Start with the Great Square of Pegasus. The northeastern corner star, Alpheratz, is technically Alpha Andromedae and serves as the starting point of the constellation. From Alpheratz, two chains of stars extend to the northeast, forming a rough V-shape that represents Andromeda's body and outstretched arms.

The brighter chain runs through Mirach and Almach, both second-magnitude stars easily visible from suburban skies. The Andromeda Galaxy lies above this chain, roughly between Mirach and the constellation's northern boundary with Cassiopeia.

The Andromeda Galaxy (M31)

M31, the Andromeda Galaxy, is the crown jewel of this constellation and one of the most important objects in the sky. Located about 2.5 million light-years away, it is the nearest large spiral galaxy to the Milky Way and contains roughly one trillion stars, making it larger than our own galaxy.

To find M31 with the naked eye, locate Mirach and look about 4 degrees to the northwest. Under dark skies, the galaxy appears as a faint elongated smudge of light about 3 degrees long, roughly six times the apparent width of the full Moon (though only the bright core is usually visible). From suburban locations, it appears as a small fuzzy spot.

Binoculars show M31 as a bright oval glow, and a telescope reveals its bright nucleus surrounded by a gradually fading disk. Two satellite galaxies, M32 and M110, are visible nearby in small telescopes. M32 appears as a compact bright spot close to the main galaxy's disk, while M110 is a larger, fainter elliptical smudge on the opposite side.

The Andromeda Galaxy and the Milky Way are approaching each other at about 110 kilometers per second and are expected to merge in roughly 4.5 billion years, forming a new larger galaxy sometimes called Milkomeda.

The Stars of Andromeda

Alpheratz (Alpha Andromedae) shines at magnitude 2.1 and is a blue-white subgiant about 97 light-years away. It is chemically peculiar, with unusual abundances of mercury and manganese in its atmosphere that make it an object of spectroscopic study.

Mirach (Beta Andromedae) is a red giant at magnitude 2.1, about 200 light-years distant. Its warm orange-red color is visible to the naked eye. Mirach serves as the key stepping-stone for finding M31, as the galaxy lies along a line extending from Mirach through Mu Andromedae.

Almach (Gamma Andromedae) is one of the most beautiful double stars in the sky. A small telescope reveals a stunning color contrast between a golden-orange primary and a blue-green secondary. The secondary is itself a close double, making Almach a triple system. This color combination rivals that of Albireo in Cygnus and is a highlight of autumn observing.

Other Deep Sky Objects

Beyond M31, M32, and M110, Andromeda contains NGC 891, an edge-on spiral galaxy often considered one of the most impressive edge-on galaxies in the sky. Its prominent dust lane cutting across a glowing disk makes it a popular astrophotography target. NGC 752 is a large, bright open cluster visible in binoculars, and the Blue Snowball (NGC 7662) is a bright planetary nebula that appears as a small blue-green disk in telescopes.

Mythology and Cultural Heritage

In Greek mythology, Andromeda was the daughter of Cassiopeia and King Cepheus of Aethiopia. When Cassiopeia boasted of her beauty, Poseidon sent a sea monster (Cetus) to devastate the coast. An oracle revealed that only the sacrifice of Andromeda would appease the gods. She was chained to a rock by the shore, but Perseus, returning from slaying Medusa, spotted her and fell in love. He used Medusa's head to turn the sea monster to stone and freed Andromeda. They married and eventually all the main characters were placed among the stars.

This story connects five constellations in one narrative arc: Cassiopeia, Cepheus, Andromeda, Perseus, and Pegasus (born from Medusa's blood). Together, they form one of the richest mythological groupings in the sky.

Best Time to Observe

Andromeda is best observed during October and November evenings, when it passes nearly overhead for mid-northern latitude observers. The Andromeda Galaxy is at its best during autumn's long, dark nights when it rides high in the sky, well away from horizon haze. The constellation is visible from August through February.

From the Southern Hemisphere, Andromeda is visible but low in the northern sky during spring months. The Andromeda Galaxy can still be observed from tropical southern latitudes when conditions are good.

Neighboring Constellations

Pegasus lies to the west, sharing the star Alpheratz. Cassiopeia is to the north, Perseus to the east, and Pisces and Aries to the south. Triangulum, a small constellation containing the Triangulum Galaxy (M33), sits just below Andromeda. Explore the royal family of autumn constellations with StarGlobe.

Quick Facts

Andromeda covers 722 square degrees, ranking 19th in size. It contains three Messier objects (M31, M32, M110). Alpheratz shines at magnitude 2.1. The constellation's right ascension ranges from about 22h 57m to 2h 39m, and its declination spans from about +21 to +53 degrees. The Andromeda Galaxy is the most distant object most people will ever see with their unaided eyes.