Andromeda Galaxy

The Andromeda Galaxy is the nearest large spiral galaxy to the Milky Way and the most distant object visible to the naked eye. At a distance of 2.537 million light-years, it appears as a faint elongated smudge in dark skies, spanning more than six times the width of the full Moon.

Andromeda contains roughly one trillion stars — about twice as many as the Milky Way — organized into a disk roughly 220,000 light-years in diameter. Its prominent dust lanes trace the spiral arms, and the bright central bulge contains mostly older, redder stars.

The 2015 Hubble mosaic resolved over 100 million individual stars across a 61,000-light-year stretch of the galaxy’s disk — the sharpest and largest image ever taken of any galaxy. The image reveals a complex history of mergers and interactions with satellite galaxies, visible as warps and distortions in the disk structure.

Andromeda and the Milky Way are approaching each other at approximately 110 km/s. The two galaxies are expected to begin merging in roughly 4.5 billion years.