《礼记·祭义》
日月一阴一阳，昼夜或长或短，终始相接，循环往复，天下的有条不紊即由此而生。
阴阳长短，终始相巡，以致天下之和。
The sun and moon, one yin and one yang, create the distinctions between day and night, between long and short days, and between the beginning and end of things. Alternately appearing and disappearing, they follow a cyclical pattern, which gives rise to the orderly functioning of the world.