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Andromeda Galaxy

A spiral galaxy 2.5 million light-years away, larger than the Milky Way and visible to the naked eye.

M31 · the nearest large spiral

Open in 3D Galaxies
  • Last reviewed 10 Oct 2026
  • 4 sources
The Andromeda Galaxy in the 2025 Hubble mosaic
NASA, ESA, B. Williams (University of Washington), heic2501a, CC BY 4.0. Resized; mosaic edge feathered.

At a glance

Andromeda Galaxy at a glance, with sources
MeasureValueSource
DistanceAbout 2.5 million light-yearsNASA Science: Hubble Messier catalog: M31 (opens in a new tab)NASA Science: Hubble Messier catalog: M31 (opens in a new tab)
TypeSpiral, SA(s)bSometimes called a barred spiral; a bar is debated.NASA Science: Hubble Messier catalog: M31 (opens in a new tab)NASA Science: Hubble Messier catalog: M31 (opens in a new tab)
DiameterDisc more than 200,000 light-years; about 260,000 ly including the haloNASA: The galaxy next door (GALEX) (opens in a new tab)NASA: The galaxy next door (GALEX) (opens in a new tab)
InclinationAbout 77°, nearly edge-onNASA Science: Hubble Messier catalog: M31 (opens in a new tab)NASA Science: Hubble Messier catalog: M31 (opens in a new tab)
Stars resolved by HubbleAbout 200 million (2025 mosaic)ESA: ESA/Hubble heic2501 (opens in a new tab)ESA: ESA/Hubble heic2501 (opens in a new tab)
Apparent sizeAbout six full Moons acrossNASA Science: Hubble Messier catalog: M31 (opens in a new tab)NASA Science: Hubble Messier catalog: M31 (opens in a new tab)
Merger oddsAbout 50% within 10 billion yearsSawala et al. 2025 (Nature Astronomy): a head-on collision within 5 billion years has only about a 2% chance.ESA: ESA/Hubble heic2508: no certainty of a Milky Way–Andromeda collision (opens in a new tab)ESA: ESA/Hubble heic2508: no certainty of a Milky Way–Andromeda collision (opens in a new tab)
First recorded964 CE by al-SufiNASA Science: Hubble Messier catalog: M31 (opens in a new tab)NASA Science: Hubble Messier catalog: M31 (opens in a new tab)
CompanionsM32 and M110 among dozens of satellitesNASA Science: Hubble Messier catalog: M31 (opens in a new tab)NASA Science: Hubble Messier catalog: M31 (opens in a new tab)

Key points

Hubble's 2025 mosaic resolved about 200 million of its stars. A future merger with our galaxy is possible but not certain.

  • Visible to the naked eye from dark sites
  • Hubble resolved ~200 million of its stars in 2025
  • Only ~50% odds of merging with us in 10 billion years

Structure

Andromeda's bright, extended bulge sits inside a disc tilted about 77° to our line of sight. Star formation concentrates in a ring about 30,000 light-years from the centre. M32, a compact companion, may be the stripped core of a galaxy Andromeda swallowed.

Collision course?

Andromeda is approaching at about 110 km/s. For years the expectation was a head-on merger in about 4.5 billion years. In 2025, Sawala and colleagues ran 100,000 simulations using Gaia and Hubble data and found roughly even odds of a merger within 10 billion years, and only about 2% for a collision within 5 billion. The Large Magellanic Cloud's pull makes a miss more likely.

What we still don't know

Its precise sideways motion, which decides whether the galaxies collide, and how many smaller galaxies it has already absorbed.

Missions

  1. 1990–

    Hubble Space Telescope

    NASA / ESAActive

    Ultraviolet to near-infrared imaging from low Earth orbit.

    Mission page (opens in a new tab)

  2. 2013–2025

    Gaia

    ESACompleted

    Mapped about two billion stars; Data Release 4 is scheduled for 2 Dec 2026.

    Mission page (opens in a new tab)

First-hand · our 3D model

How we render it

Andromeda is the ESA/Hubble heic2501a mosaic (CC BY 4.0), shown on a camera-facing panel whose roll is locked to world up, so the galaxy never turns edge-on or spins as you orbit. The mosaic's ragged edge is feathered into transparency, and an analytic bulge-plus-disc light profile underneath lets the edge dissolve into the galaxy's own glow.

The Hubble mosaic stops just south of the nucleus. Rather than show a hard cut, the renderer completes that region from the point-symmetric opposite side of the galaxy. Foreground Milky Way stars sit in front of the image to give real parallax when you move.

Open Andromeda Galaxy in 3D How we built the modelInteractive 3D services

Sources

  1. NASA Science: Hubble Messier catalog: M31 (opens in a new tab)
  2. NASA: The galaxy next door (GALEX) (opens in a new tab)
  3. ESA: ESA/Hubble heic2501 (opens in a new tab)
  4. ESA: ESA/Hubble heic2508: no certainty of a Milky Way–Andromeda collision (opens in a new tab)

Image credit: Hubble 2025 mosaic: NASA, ESA, B. Williams (University of Washington), CC BY 4.0

Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.