Why can we see rainbows after rain? 我们雨后为什么能看到彩虹？

　　We can see rainbows after rain because droplets of moisture in the air work like a big prism. 这是因为空气中的水滴就像一个大棱镜。

　　So what is a prism? 那么什么是棱镜呢？

　　It is a piece of glass. It usually has a triangular shape. 它是一块玻璃，通常有三角。

　　What does the prism do? 棱镜的作用是什么？

　　It reflects and separates light. 它能反射和分散光线。

　　When we look at sunlight, it seems white. 我们看阳光时，它似乎是白色的。

　　However, if you see sunlight through a prism,  但如果你透过棱镜看到阳光的话，

　　you'll know that there are different colours from red to violet in the white light, just like a rainbow. 你就会知道，白光中有不同的颜色，从红到紫，就像彩虹一样。

　　Because of prisms, we know that sunlight is a mixture of different colours. 因为棱镜，我们知道太阳光是不同颜色的混合物。