sun前面要加the。

宇宙中被命名的东西很多都是独一无二的，如太阳sun月亮moon地球earth等。

the Great Wall 长城也是被特指的专所以也用the

The sun was low in the sky.

太阳低挂在天空。

Although the sun was shining it wasn't very warm.

尽管太阳高照，却不很暖和。

The sun was already up when they set off.

他们出发时太阳已经升起了。

She rolled over to let the sun brown her back.

她翻了个身，让太阳把她的背晒黑点。