极光是一种美丽的自然现象，常常出现在很冷的地方，比如北方的天空。

"极光" is a beautiful natural phenomenon often seen in very cold places, like the northern sky.

晚上的时候，天上会出现绿色或者红色的光，非常好看。

At night, green or red lights appear in the sky, which look very beautiful.