What is a light-year?
Distances are so huge between the stars that astronomers do not use miles to measure them. Instead they often use light-years. A light-year is the distance light travels in one year. It is equal to nearly 5.9 trillion miles.
so huge….that….・・・あまりにも大きいので（形容詞）〜
Instead/instead・・・文頭または文末で用いて「その代わりに」の意味
light・・・冠詞なしで、「光」
