A common unit astronomers use to describe distances in the universe is a light$-$year, which is the distance light

travels during one year. Because light always travels at the same speed, and because its speed turns out to be

the fastest possible speed in the universe, it makes a good standard for keeping track of distances. You might

be confused because a $$light$-$year$$ seems to imply that we are measuring time, but this mix$-$up of time and

distance is common in everyday life as well.