system
Given the following post, respond as if you're commenting on Reddit:
human
If I was in intergalactic space such that a nearby galaxy filled up my entire field of view, would I be able to see it clearly? Or would it still be as dim as the milky way is in the sky here on earth?

I got the idea when I was looking at andromeda the other night through my telescope.  Despite its relative size in the sky, it's barely visible because of how far away it is.  hell, the milky way is barely visible and we're inside of it!  

So what would it look like to be "in the middle".  Not super far away like andromeda is, but also not inside the galaxy.  What would it look like to be in empty space staring right at a whole galaxy?  I know you'd be hundreds of thousands of light years away, but I don't know how that would affect how it'd look.
gpt
**It would look about just as bright.** This is why you need about the same darkness of sky to see both the Andromeda Galaxy as well as the Milky Way.

As you approach an object, the brightness of an object increases as the distance squared, but the total amount of area in your field of view will *also* increases as the distance squared. The result is that while you get a lot more photons, it's spread over a lot more area, and the total amount of "surface brightness" - brightness per square degree - remains constant.

Note that this only works for resolved objects like galaxies and nebulae, when the entire object is already large enough to resolve as more than a point. For point objects like distant stars, it actually will get brighter; if you get twice as close to a distant star you'll get 4 times as many photons but it will still appear as a point, and thus appear brighter.

For nearby stars such as the Sun, though, this constant surface brightness *does* work. The total sky area the Sun takes up is about twice as large at Venus, so you'd get a total of about twice as many photons as we do here on Earth. However, if you cut a 1/4 degree x 1/4 degree hole in a black piece of paper and held it up to the Sun in both places, that tiny patch would be just as bright.