In the sunlight, my melody may still sound airy. It is as transparent as crystal, as clear as the cloudless blue sky, and as a silver river breaking the ice.

阳光下我轻快的曲调或许依旧如水晶般轻盈透明，如银色的河流冲破坚冰，如同北国清冷透彻，不容云翳的蓝色天空。

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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