Why there is a rainbow after the rain in summer？
We can always see a rainbow after the rain in summer. Because there are a lot of small drops of water in the air after the rain. Light changes direction when passing through the drops at an angle, which is called refraction. If the drops are bigger, the rainbow will be easier to be seen. In winters, drops of water can seldom exist in cold air, and there is seldom a shower. So the rainbow usually cannot be seen in winters.
夏天的雨后，天空常常出现半圆形的彩虹，这是因为在雨后，空气中会有大量的小水滴悬浮在空中，当光线经过这些水滴时，光就会出现折射现象，又因为在光的折射过程中，橙黄绿蓝靛紫等色光的折射角度不相同，就形成了我们所看到的彩虹。彩虹的明显程度，取决于空气中小水滴的大小，小水滴体积越大，形成的彩虹越鲜亮，小水滴体积越小，形成的彩虹就不明显。一般冬天的气温较低，在空中不容易存在小水滴，下阵雨的机会也少，所以冬天一般不会有彩虹出现。
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