Thanks for the question! When you hear the term “light year” you probably think of time, but a light year actually measures distance. On Earth we measure distance with units like feet or meters, but when you get something as far away as another planet, feet aren’t really a practical unit of measurement. Take the sun for example - it’s 93 million miles away. That’s a pretty big number! So instead, we use light years. Light years are based on how long it takes for light to travel, which is 186,000 miles per second. When you turn on the light in your room, you might say that the lightbulb is 1 light second away from the switch (it’s a lot less but when you can physically see the lightbulb it doesn’t really matter). Pluto is a bit different - you can’t just look over and see it. If we flipped a switch on Earth, it would take a bit longer for it to turn on a bulb on Pluto. For this reason, we would say that the bulb is 320 light-minutes away. That’s a bit more manageable than 93 million right? To answer your other question, since light takes time to travel, we can see light over a distance before it reaches us. If we turned on the light switch on Pluto, it would take a few minutes for the bulb to light up, even thought the switch is already flipped. Similarly, if we flipped it off, the light bulb on Pluto would remain on until the light were able to travel to the socket, and if we were to look at Pluto through a telescope, we would see the bulb stay lit until the light had time to reach it, even though the switch would be off. Similarly, when we look at stars that have exploded, the light from them hasn’t reached us yet, so when we look at them from a distance they’ll appear to still be lit, even though their “switch” has been flipped long ago. We hope this helps!
if you have any more space questions, feel free to ask us!