Andromeda, the Chained Princess

A chain of stars from the corner of the Great Square

Andromeda starts at Alpheratz, the northeast corner of the Great Square of Pegasus, and runs northeast through Mirach to Almach, three second-magnitude stars about equally spaced.

• Mirach to M31: from Mirach step northwest to μ And, then the same distance again to ν And. The Andromeda Galaxy is the oval glow just beyond ν.
• Mirach to M33: go the same distance from Mirach on the opposite side, southeast, to reach the Triangulum Galaxy in Triangulum.

High on fall evenings in the north, low in the south

Andromeda is highest at 9 pm in November and passes overhead from mid-northern latitudes. From the Southern Hemisphere it stays low in the north: from 35°S the Andromeda Galaxy rises only about 15° above the horizon.

Andromeda's best targets are galaxies, led by M31

Andromeda lies away from the plane of the Milky Way, so its deep-sky list is mostly galaxies. Three Messier objects, M31, M32 and M110, are one galaxy and two of its satellites. Three Caldwell objects are here too: the Blue Snowball, NGC 891 and NGC 752.

Turned sideways: the stars are 100 to 400 light-years away, the galaxy 2.5 million

Alpheratz is 97 light-years away, Mirach 199 and Almach 390. Inside the Milky Way, NGC 752 lies at 1,400 light-years and the Blue Snowball at about 6,000.

The Andromeda Galaxy is 2.5 million light-years away, M32 and M110 about the same. The light reaching your eye tonight left before Homo sapiens existed. NGC 891 is 13 times farther again, at 32 million light-years.

Brightest stars in Andromeda

Every cataloged object in Andromeda

The table above is the short list. Below is everything the major catalogs place inside Andromeda's IAU boundary, mostly galaxies. Open a catalog to see its brightest members. Each list shows up to 25; longer lists link to the full catalog page.

The galaxy that proved there are other galaxies

• Edwin Hubble's Cepheid. On a plate taken in October 1923 at Mount Wilson, Hubble found a Cepheid variable star in M31. Its period gave a distance far beyond the Milky Way, settling the debate over whether spiral "nebulae" were separate galaxies. He marked the plate "VAR!".
• A future merger. M31 is approaching the Milky Way at about 110 km per second. A 2025 study using Gaia and Hubble data put the chance of a merger within the next 10 billion years at about 50%, lower than earlier estimates.
• Streams of stars. The Pan-Andromeda Archaeological Survey mapped a halo of stellar streams around M31, the remains of smaller galaxies it has torn apart, including the Giant Stellar Stream.
• Upsilon Andromedae. In 1999 it became the first Sun-like star found to host more than one planet. It has at least three gas giants.

Andromeda video tour

Andromeda Constellation Deep Sky Tour: Galaxies & Nebulae · Watch on YouTube

The princess chained to the rock

In Greek myth Andromeda was the daughter of Cepheus and Cassiopeia. To punish her mother's boast, she was chained to a rock as a sacrifice to the sea monster Cetus, and rescued by Perseus. All five figures are neighbors in the sky.

The Persian astronomer al-Sufi recorded the Andromeda Galaxy as a "little cloud" in his Book of Fixed Stars around 964, the earliest known record of it. In Chinese astronomy many of Andromeda's stars belong to Kui (奎), the Legs, one of the 28 lunar mansions.

Constellations bordering Andromeda

Andromeda shares its IAU boundary with 6 constellations.

• Cassiopeia
• Lacerta
• Pegasus
• Perseus
• Pisces
• Triangulum