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Find the Great Square of Pegasus first (see Pegasus). Andromeda's own brightest star, Alpheratz, sits at the square's northeast corner — officially an Andromeda star, even though it also closes off Pegasus's shape; the site's own chart draws it once and lets both figures share it. From Alpheratz, one chain of stars runs through Delta, Mirach, and Mu; a second, shorter branch runs from Mirach out to Almach, near the border with Perseus. The galaxy M31 sits a short binocular-hop north of Mirach. Best viewed on clear, moonless autumn evenings — late September through November.

RA is in decimal hours, Dec in decimal degrees, both J2000 — the same figures the site's own chart is drawn from. Magnitudes are visual.

Star	RA (h)	Dec (°)	Mag	Spectral type	Distance	Name
Alpheratz (α And)	0.140	29.09	2.06	A0p, chemically peculiar binary	~97 ly	Arabic surrat al-faras, "the horse's navel" — a leftover from when the star was reckoned part of Pegasus
δ Andromedae	0.655	30.86	3.27	K3 III giant	~105 ly	No traditional name
Mirach (β And)	1.162	35.62	2.05	M0 III red giant	~198 ly	Arabic al-maraqq, "the loins"
Almach (γ And)	2.065	42.33	2.10	K3 bright giant, multiple star	~358 ly	Arabic ʿAnaq al-Arḍ, roughly "the earth-lynx"
μ Andromedae	0.947	38.50	3.86	A5 V main sequence	~130 ly	No traditional name

Almach is worth pointing a small telescope at even without a star chart: the gold-and-blue color contrast between its two brightest components is one of the more striking double-star views in the northern sky.

M31 sits close enough and is bright enough — magnitude 3.4–3.5 — to be visible to the naked eye from a dark sky as a faint, elongated smudge, without optical aid; it is routinely cited as the most distant object most people will ever see unaided. The Persian astronomer Al-Sufi recorded it in his Book of Fixed Stars in 964 CE as a "little cloud," and Simon Marius became the first to look at it through a telescope, in 1612.

For most of the early twentieth century, astronomers argued over whether objects like this "cloud" were nearby gas clouds inside our own Milky Way or entire separate galaxies far beyond it. That argument came to a head at the so-called Great Debate, held at the Smithsonian on 26 April 1920, where Harlow Shapley argued for one large Milky Way containing everything, and Heber Curtis argued that spiral nebulae were "island universes" in their own right — a debate that ended without a clear winner on the night. The deciding evidence came three years later: in October 1923, Edwin Hubble, using the 100-inch telescope at Mount Wilson, identified a Cepheid variable star on a photographic plate of M31 (he marked it "VAR!"), and by applying the period–luminosity relation described on the Cepheus page, calculated a distance far too great for the object to be inside the Milky Way. He had found a dozen Cepheids in M31 by the end of 1924, and the result — read on his behalf at a meeting of the American Astronomical Society on New Year's Day 1925 — effectively settled the debate. Hubble's own first distance estimate, about 900,000 light years, was too low because he did not yet know that Cepheids come in two distinct types with different period–luminosity relations; the modern, Gaia-refined figure is closer to 2.5 million light years.

The galaxy and the Milky Way are approaching each other, and for over a decade the standard prediction — from a 2012 Hubble Space Telescope study that directly measured M31's sideways motion across the sky — was a head-on collision in roughly 4.5 billion years. A 2025 reanalysis combining Hubble and Gaia data, accounting for the pull of the Large Magellanic Cloud, found the outcome is less certain than that: only about a 50–50 chance of a collision within the next 10 billion years, though a roughly 2% chance remains that it happens on the original, much faster 4–5 billion year timeline. Which is to say: the two galaxies are on a collision course, in the sense that their paths converge, but whether they actually collide is now an open scientific question rather than a settled one.

Object	Catalog	Type	Notes
—	M32 (NGC 221)	Elliptical galaxy	The brighter of M31's two prominent satellite galaxies, visible in the same low-power field as the main galaxy.
—	M110 (NGC 205)	Dwarf elliptical galaxy	M31's other well-known satellite, larger but dimmer than M32.
—	NGC 891	Edge-on spiral galaxy	Not a satellite of M31 — a background galaxy roughly 30 million ly away, prized for its dark dust lane.
—	NGC 752	Open cluster	Loose and bright, about 60 stars, a good binocular target.
Blue Snowball	NGC 7662	Planetary nebula	Small and bright, roughly 4,000 ly away; needs a telescope.

Andromeda's mother, Cassiopeia, boasted that she (or her daughter, depending on the telling) was more beautiful than the Nereids, the sea nymphs — an insult Poseidon answered by sending the monster Cetus to ravage her father Cepheus's coastline. An oracle said the only remedy was to sacrifice Andromeda to the monster, so she was chained to a rock by the sea; Perseus, passing by with Medusa's head, killed Cetus and claimed her as his wife, over the objections of Phineus, to whom she had already been promised. The catasterism — turning the players into constellations — is recorded in Eratosthenes' Catasterismi and Hyginus, with Ptolemy listing Andromeda among the Almagest's 48; the fullest narrative telling is Ovid's Metamorphoses, Book 4.

Chinese astronomy read this same stretch of sky on entirely different terms. Most of Andromeda's own stars — Beta, Mu, Nu, Pi, Delta, Epsilon, Zeta, and Eta — together with several stars over the modern border in Pisces, formed Kui, "Legs," one of the twenty-eight lunar mansions used to track the Moon's monthly progress through the sky; an older, Neolithic-era name for the same grouping was Tianshi, "the Celestial Pig." Neither the pig nor the legs has anything to do with a chained princess — a reminder, as with Leo's lion, that constellation figures were drawn independently by different cultures looking at the same stars, not received from one another.

Date	Event
c. 240 BCE	Eratosthenes' Catasterismi fixes Andromeda among the mythological star figures.
c. 150 CE	Ptolemy catalogues Andromeda among the 48 constellations of the Almagest.
964 CE	Al-Sufi records M31 as a "little cloud" in the Book of Fixed Stars.
1612	Simon Marius makes the first telescopic observation of M31.
26 April 1920	The Shapley–Curtis "Great Debate" over the scale of the universe, held in Washington, D.C.
Oct 1923 – 1925	Hubble identifies Cepheids in M31 and effectively settles the debate.
2012	A Hubble proper-motion study predicts a Milky Way–Andromeda collision in ~4.5 billion years.
2025	A Hubble/Gaia reanalysis finds the collision is no longer a certainty.

• Perseus — rescues Andromeda from Cetus and marries her.
• Cepheus — her father, king of the threatened kingdom.
• Pegasus — shares its brightest corner star, Alpheratz, with Andromeda.