《汉书·志·天文志》
若烟非烟，似云非云，郁郁葱葱，萧疏地分布着形如圆形困仓的云气，是所谓庆云。
若烟非烟，若云非云，郁郁纷纷，萧索轮囷，是谓庆云。
As if smoke but not smoke, as if clouds but not clouds, a luxuriant mass, sparsely scattered like round towers  and battlements – these are called Lucky Clouds.