[actionfromafar]

But did we know they were galaxies and not just some shining object?

[macintux]

Their nature wasn’t confirmed until the 20th century. Wikipedia tackles the history: https://en.wikipedia.org/wiki/Andromeda_Galaxy

[ahazred8ta]

> In 1924, Edwin Hubble established the distance to classical Cepheid variables in the Andromeda Galaxy, until then known as the "Andromeda Nebula" and showed that those variables were not members of the Milky Way. Hubble's finding settled the question raised in the "Great Debate" of whether the Milky Way represented the entire Universe