I hoped that every day is the cloudless day.

我希望每天都万里无云。

youdao

The next day dawned cloudless and fair.

第二天天亮了，万里无云，天朗气清。

youdao

It was a cold autumn day with a cloudless, hazy sky and a yellow sun that no longer gave off any heat, the kind you can look at directly without hurting your eyes.

那是个寒冷的秋日，天空朦胧，万里无云，黄色的太阳不再发射出热量，是那种任你直接看都伤不到你的眼睛的太阳。

youdao

But a clear, cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more easily than they do red light.

BBC: rainbow