system
Given the following post, respond as if you're commenting on Reddit:
human
If some stars are dead already, even with their light still reaching us, how are we able to tell which ones are still in existence?
gpt
If we look at the light from a star and see that it is at the end of its life cycle (say, we can say with confidence it will die in 100 to 1000 years), and if the star is 10,000 light years away, we can say with confidence it has already died.