Light-year
noun
What happens when light travels a year? You have a light-year.
こうねん
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
ちきゅうから月までは、一おく分の四光年です。
It is four one hundred millionths of a light-year from the earth to the moon.
ポートランドの中しんから北の方に四光年すすんだら、どこにつきますか。
If we go north from the center of Portland for four light-years, where will we be?
光年とは、光の速度で1年間進み続け到達出来る距離だ。貴様が俺と対決しようなんて、一万光年早いわ。
A light-year is the distance that light can travel over the course of one year. You are 10,000 light-years too early to be facing me.