Andromeda (M31)

Object Type: Spiral Galaxy
Scope APO 80mm, 21 hours color/broadband & 9 hours narrowband

The Andromeda Galaxy (Messier 31, NGC 224) is the nearest large spiral galaxy to the Milky Way, about 2.5 million light-years away in the constellation Andromeda, and the most distant object easily visible to the naked eye. It is the largest galaxy in our Local Group and holds roughly one trillion stars, about twice as many as the Milky Way, though the two are comparable in total mass. Edwin Hubble settled the 1920 "Great Debate" in 1925 by finding Cepheid variable stars in M31, proving it lies far beyond our own galaxy. Andromeda is approaching us at roughly 110 km/s; the two galaxies have long been expected to merge in about 4.5 billion years, though recent (2024) analyses suggest the collision is closer to a coin-flip and may not happen at all.