In astronomy the term "red shift" denotes the extent to which light from a distant galaxy has been shifted toward the red, or long-wave, end of the light spec¬trum by the rapid motion of the galaxy away from the Earth. 我有些忘记怎样翻译定语从句了,想跟大家确定一下这句话to which是不是指代先行词extent?如果把这句话顺过来应该是啥样的?