Andromeda Galaxy
Nearest major galaxy, on a collision course with the Milky Way.
Overview
The Andromeda Galaxy (M31) is the nearest major galaxy at 2.5 million light-years, containing ~1 trillion stars on a collision course with the Milky Way.
Why It Matters
Galaxy mergers shape cosmic evolution. Andromeda is our future — in ~4.5 billion years the Milky Way and Andromeda will merge into 'Milkomeda.'
Scientific Explanation
M31 is a spiral galaxy similar to but larger than the Milky Way. Radial velocity measurements (1912) showed it approaches us at ~110 km/s. Computer simulations predict a major merger, though individual star collisions are rare due to vast interstellar distances.
Historical Background
Known as the 'Little Cloud' since ancient times. Hubble (1923) resolved Cepheid variables in Andromeda, proving extragalactic distance — the universe expanded by billions of light-years overnight.
Visual Explanation
Simulation: two spiral disks interpenetrate, tidal tails form, cores merge over billions of years. The night sky would eventually show a vast elliptical glow.
Key Discoveries
- ✦ Hubble's Cepheids prove Andromeda is external (1923)
- ✦ Andromeda approaching — Milky Way merger predicted
- ✦ M32 and M110 satellite galaxies
- ✦ Gaia refines proper motion of M31
Important Astronomers
Interactive Simulation
Simulate the Milky Way-Andromeda merger over billions of years.
Galaxy Collision — Visual Lab
Open in Visual Lab →Reflection Prompt
Humanity may not exist in 4.5 billion years — but the merger will create new stars. What persists beyond species?
Write in Journal →