translation.en: If you live up here, in summer the sun is coming fairly directly down, but in winter it's coming through a huge amount of atmosphere, and much of the ultraviolet is weeded out, and the range of wavelengths that hit the Earth are different from summer to winter.
translation.zh: 如果你住在 太阳光在夏季几乎是直射的 而在冬季就会斜穿厚厚的大气 很多紫外线无法到达地面 而到达地面的波长范围 夏天和冬天是不同的