system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What do we ACTUALLY know about anything regarding galaxies outside of the Milky Way?

And how the fuck do we know it?
gpt
We know whatever we can see. Some of what we know we know because we can *literally see it*, like with our own eyeballs through magnification. The rest comes from using machines to "see" light that our eyes aren't sensitive to, like radio.

So basically, we look, then we measure what we see, then we figure out what those measurements imply.

Fun fact: We know far *less* about our own galaxy and its neighbors than we know about galaxies tens of millions of light-years away. Why? Because we can *see* those far-away galaxies, while the up-close ones are obscured by nearby clutter. For instance, it was just discovered a few years ago that our own galaxy is even right now in the process of colliding with another galaxy which nobody ever knew was there. It was too close, too big-in-the-sky and too obscured by stuff in between for us to notice it until just a few years ago.