sky

Not a single cloud was visible in the clear blue sky on that extremely hot summer afternoon.

(Chinese) 在那个异常炎热的夏日午后，晴朗的蓝天中见不到一丝云彩。

Astronomers use powerful telescopes to observe distant galaxies and stars in the deep night sky.

(Chinese) 天文学家利用功能强大的望远镜观察深邃夜空中的遥远星系和恒星。