今晚天空很清澈。
Jīn wǎn tiān kōng hěn qīng chè
Tonight sky very clear.
Simple
今晚天空晴朗，可以看到好多星星。
Jīn wǎn tiān kōng qíng lǎng, kě yǐ kàn dào hǎo duō xīng xīng
Tonight sky clear, can see many stars.
晴朗 = clear and bright
今晚万里无云，繁星点点，连银河都看得清清楚楚！
Jīn wǎn wàn lǐ wú yún, fán xīng diǎn diǎn, lián yín hé dōu kàn dé qīng qīng chǔ chǔ!
Tonight ten-thousand-mile no-cloud, stars dot-dot, even the Milky Way can be seen clearly!
万里无云 = ten thousand miles without cloud = idiom for perfectly clear sky; 繁星点点 = stars dotting the sky, poetic
More Chinese (Mandarin) Weather Phrases