The size of Andromeda galaxy in night sky. We don't see it like this as it's dimmer than shown in picture. But regardless it's as large in the sky beside the moon.
Interestingly before 1920s humans weren't aware of any other galaxy even though they could see those, and the milkyway was their whole universe. It's after discovery of theory of relativity that humans could measure distance of heavenly bodies and figure out which one are distant galaxies.
Everything was counted as Nebula before that, clouds of gases in our milkyway. Nebulas are still in the sky, but galaxies though look like Nebula are far far away and larger.
#astronomy
