If an object - a star, for instance, like our own sun - is eight hundred light years away from the Earth, it would take light leaving that object eight hundred years until it reached our eyes. So when you look at that object, you are seeing it as it appeared eight hundred light years ago, not as it looks today. It might not even exist anymore. Every time you look up at the stars, you are looking into the past.
Wendy Mass, Jeremy Fink and the Meaning of Life
past, stars