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GALEX · Andromeda in ultraviolet
GALEX · Andromeda in ultraviolet · NASA/JPL/California Institute of Technology

Andromeda Galaxy

Galaxy in Andromeda · 2.5 million light-years

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The Andromeda Galaxy (M31) is the nearest large galaxy to our own — about 2.5 million light-years away, roughly 150,000 light-years across, home to around a trillion stars — and under a reasonably dark sky it is the farthest thing most human eyes can see unaided. Find it from September onward by following the deeper dip of Cassiopeia's W, which points almost straight at it.

TypeGalaxy
ConstellationAndromeda
Right ascension0h 42m 43s
Declination+41° 16′
Object distance2.5 million light-years
Also known asM31
Imaged byHubble, JWST
The nearest large galaxy to our own and the most distant object visible to the naked eye. A spiral of a trillion stars approaching the Milky Way — the once-certain collision is now put at roughly even odds within ten billion years.

Observing Andromeda Galaxy

Andromeda Galaxy lies in the constellation Andromeda and is best placed in the evening sky around September. Its maximum altitude above the horizon depends on your latitude. It is best placed for observers in the northern hemisphere, and sits low for those far south. Note that the listed magnitude is spread across the whole object — diffuse galaxies and nebulae are often harder to see than the number alone suggests, so dark, moonless skies help a great deal.

The farthest thing your eyes can see

At magnitude 3.4, Andromeda is genuinely visible without any equipment — a small elongated smudge under a reasonably dark sky. What your eye catches is only the galaxy's bright core: photographed properly, Andromeda is wider on our sky than six full Moons in a row. The light hitting your retina tonight left the galaxy around the dawn of early stone-tool making, some two and a half million years ago.

Distance is the thing that transformed Andromeda from a 'spiral nebula' into a galaxy in its own right — and Cepheid variable stars, the classic 'standard candles' that first settled that century-old debate, still anchor its distance today, now pinned to better than two percent. In 2025 the Hubble Space Telescope completed its largest photomosaic ever made — 2.5 gigapixels of Andromeda, resolving hundreds of millions of its stars individually.

The collision that isn't certain anymore

For years, popular astronomy repeated a confident story: Andromeda is approaching the Milky Way at about 110 kilometres per second, and in a few billion years the two must collide and merge. Half of that is still measured fact — the approach speed is real. The conclusion is not: modelling published in 2025, which folds in the gravitational influence of the Local Group's other members and the measured sideways motion, puts the odds of a merger within the next 10 billion years at roughly a coin flip.

If they do merge, the two spirals would settle into a single elliptical galaxy — and yet individual stars would almost certainly never collide with each other; the distances between stars are simply too vast. Both galaxies remain the two heavyweights of the Local Group either way.

How to find Andromeda Galaxy tonight

From September onward, Andromeda climbs the eastern sky after dark and stays well placed through northern autumn and winter evenings.

The reliable star-hop starts at Cassiopeia — the bright W (or M) of five stars that never sets for most northern latitudes. The W has two dips; the deeper one works like an arrowhead and points almost straight at Andromeda, about fifteen degrees away. Sweep that line with your eyes or binoculars and look for a small elongated glow.

Expectations matter: with the naked eye you are looking for a faint smudge, not a photograph. Binoculars show the bright core plainly and hint at the disc's extent; dark, moonless skies make the biggest difference of all, because the galaxy's light is spread across a huge area.

For your exact sky, open Andromeda in the 3D map — the Tonight panel computes visibility and direction for your location, and the map can then carry you across the 2.5-million-light-year gap to see the galaxy's position in the real three-dimensional neighbourhood.

The numbers — and how sure we are

Every value below carries its label from the episode research pack: MEASURED (observation-derived), ESTIMATE (model-derived or uncertain), COMPARISON (an analogy for scale), VISUALIZATION (explanatory rendering).

Questions people ask

Will the Andromeda Galaxy collide with the Milky Way?

It is no longer the certainty it was long presented as. Andromeda's approach speed (~110 km/s) is measured fact, but 2025 modelling that includes the rest of the Local Group and the measured sideways motion gives roughly even odds of a merger within the next 10 billion years. If a merger does happen, the result would be a single elliptical galaxy — with essentially no individual stars colliding, because interstellar distances are so vast.

Can I see Andromeda without a telescope?

Yes — that is its claim to fame. At magnitude 3.4 it is visible to the unaided eye under a reasonably dark sky, making it the farthest object most human eyes can see: about 2.5 million light-years. Expect a small elongated smudge near Cassiopeia, not the sweeping spiral of photographs — your eye only catches the bright core.

How big is Andromeda in the sky?

Far bigger than most people guess: photographed deeply, it spans more than six full Moons placed side by side. The disparity between that and the tiny smudge you see by eye comes down to surface brightness — the light is real but spread thin, which is why dark skies and low-magnification, wide-field instruments show it best.

How many stars does Andromeda have?

Roughly a trillion — several times the Milky Way's star count, spread across a disc around 150,000 light-years wide (where you call the 'edge' is genuinely fuzzy). In 2025 Hubble's largest-ever photomosaic resolved hundreds of millions of them individually along one flank of the galaxy.

See Andromeda Galaxy in Universe Finder

Open the interactive 3D map to fly to Andromeda Galaxy and see it in context among the real stars around it. Launch the 3D view →

Prefer to watch first? Watch the full Andromeda Galaxy episode — a guided 3D flight with chapters, transcript and sources →

Sources

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