Light-year
noun, suffix
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.
月からニ光年先に小さい石が見える。
You can see a small rock two light years away from the moon.
このロケットで一光年先に行くとすると一万年はかかります。
With this rocket it would take at least take 10,000 years to travel one light year.
一光年はセグウェイで何日かかるんだろう。
I wonder how many days it would take to travel one light year on a Segway.