system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 How do astronomers know a star/planet they are observing has already been discovered/named by others or not?
gpt
Stars have coordinates in the sky, and most of them are so far away that they don’t move at all in a human lifetime or more. So astronomers can check with existing star maps or charts to see if what they are observing is something new or not.