Title pretty much covers the question.
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I mean, its the second thing.
You see light when that light hits your eyeballs, and your eyeballs are (hopefully) where you are.
That’s why we say we see stuff as it looked like “in the past.” That light from a star 10 LY is light that was emitted 10 years ago back at that star, weird freaky relativity stuff not withstanding.
We’re seeing it as it was 10 years ago; that’s the amount of time it took for the light to get here.
You could think of it like, if the moon was 10 light years away, and we could see someone turning on a flashlight for 1 year, then off forever, it’d still take 10 years to get to us (when we’d see it).
To us we’d see that flashlight on for another year, that’s how long they kept it on. But to them, they turned off the flashlight 9 years ago.
We are seeing light that is 10 years old relative to Earth. A light year is just a measure of the distance light travels in a vacuum in 1 earth year. If that star died out at the moment you’re observing it, it would take 10 years before the point of light would disappear from our sky and we’d have no way of telling otherwise until then. As any other indication of the loss of the star would take 10 years to reach us (or more)
But how many years would it take to reach earth from the lights perspective?
So, when an airplane is overhead and it’s high, but not so high up you can’t hear it, it sounds a lot like the airplane is a lot farther behind than where you see it, right?
That’s because the light gets to your eyes way faster than the sound does.
So while you’re basically seeing it where it is in real time, the sound takes longer to get to you so you hear it farther behind.
Now stretch the distance out soooooooooooooooooooo far that like takes time to get to you, and it’s the same idea.
We’re seeing the light as it reaches us, and it’s been travelling for 10 years from our perspective.
Fun fact; given the expansion of the universe, by the time we see the light that came from 10LY away, the actual distance to the star now is more than 10LY (not by much, but the further you go, the more pronounced the effect).
It’s both, we are seeing the the light as it reaches us and the light depicts the state of the star when the light departed it.
You are always “just seeing light when it reaches us”. That is how looking at things works.
Let’s take the screen in front of you for example: The display emits light and the light travels through the air until it hits the photo receptive cells in your eye and the eye then sends a signal to your brain. Because the screen is so close to you, the light only takes a tiny tiny fraction of a second to reach your eye, but technically speaking you are always seeing light from the past.
If you walk up a mountain at night and look at the lights from the city below, because the distance is greater, that light takes a little bit longer to reach your eyes, but it’s still a miniscule fraction of a second.
If you look at the sun (which you shouldn’t do because it can damage your eyes) it is way farther away. It’s so far away that the light takes roughly 8 minutes to reach you, therefore you look 8 minutes into the past. One could say the distance to the sun is 8 light minutes.
And if you look at a star that is 10 light years away, the cells in your eyes react to light that has traveled through the universe for 10 years before it reached you.
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