天气要变坏时,一般先在高空出现淡淡的云,这种云有点像鸟类的羽毛,叫做卷云。不久,卷云的下面又会出现含雨的卷层云。卷层云一般是在6千米以上的高空出现,那里的温度很低,云中的小水滴都变成了六棱柱状的小冰晶。月光通过云层时,照到小冰晶上会发生折射,使我们看到在月亮的周围出现一个白色的圆圈,这在气象学上叫做月晕。 When the weather is going to deteriorate, there is generally a faint cloud first in the sky. The cloud is a bit like a bird’s feather called a cirrus cloud. Soon, there will be rain under the cirrus clouds roll clouds. Coil clouds are generally above 6 km altitude, where the temperature is very low, the clouds of water droplets have become a small prismatic hexagonal ice crystals. When the moon shines through the clouds, it shines on the small ice crystals, causing us to see a white circle around the moon, which is called moon halo in meteorology.