Comparison to Western Concepts: The most common word for “sky” is
天空 (tiānkōng), which is like the English word “sky”—neutral and used in everyday conversation (e.g., “The sky is blue today”).
苍穹 (cāngqióng) is much closer to the English words “firmament” or “the heavens.” Like “firmament,” it has a literary, slightly archaic, and poetic feel. However, while “firmament” often has biblical or creationist undertones in English, 苍穹 is more connected to a philosophical and naturalistic sense of wonder.