Once again from my son's workbook.
It discussed standing on a planet 65 million light years away from Earth, with an extremely powerful telescope pointed at Earth. It claimed that then you could see the dinosaurs if that was the case.
Yes, that's true, though whether you could actually see dinosaurs is debatable because from 65 million light years away they'd be pretty small :-)
The reason is very simple. When you look at a dinosaur you're seeing the light reflected from the dinosaur's skin. That light travels at a finite speed, so it takes a finite time to get from the dinosaur's skin to you. If you're a light year away from the dinosaur what you're seeing is the light reflected off the dinosaur's skin a year ago.
To The Star
by Mihai Eminescu, 1886
To the star up in ethereal heights
Maybe it perished long ago
The icon, gently soaring high,
Alike when our desire grown old