in the sun，在阳光普照下，沐浴在阳光下面，也可引申为 光明磊落。under the sun，在太阳直射下，烈日当头时使用。
We sat in the sun.
She sat in the sun, idly sipping a cool drink.
I'm perfectly content just to lie in the sun.
The leaves will scorch if you water them in the sun.
Don't stay out in the sun for too long ─ you can't be too careful.
The diamond shone with every hue under the sun.
We talked about everything under the sun.
We sat there for hours talking about everything under the sun
The fashion-conscious will go for anything under the sun!
To a sophisticated person there is nothing new under the sun.; He who has sailed the seven seas doesn't think much of mere rivers.