system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If the Andromeda Galaxy is roughly 220,000 light years in diameter, how can we know what it actually looks like at any given moment? (since the light from the far end is 220,000 years behind the light at the closer end)
gpt
Because 220,000 years is not very long in terms of the time it takes stars to move much relative to the whole galaxy. It is something like 0.1% of the rotation time of the galaxy arms. So the light from one end and the other are not off by much.

So, the farthest point is about 0.1% off of the closest point in terms of what they actually are compared to what they look like.