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.
It is four one hundred millionths of a light-year from the earth to the moon.
If we go north from the center of Portland for four light-years, where will we be?
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.