Look at various parts of the sky on a clear day and you will see that it is not a uniform blue.
抬头仰望天空，你会发现在晴朗的日子里，天空并不会呈现出统一的蓝色2IX@E*JfrjS3。
Even if the sky is deep blue when you look straight up, near the horizon it is lighter.
即使你头顶上正对的这片天是深蓝色的，靠近地平线处的也会相对较浅一些5Rh4!f&CMEupo。
This is partly due to pollution, but even in the cleanest air the sky is lighter near the horizon due to the effect of earth's atmosphere on sunlight.
部分原因要归咎于污染，但是就算是在最干净的空气中，贴近地平线处的天空颜色也会比较浅，这是由于地球大气层对阳光的影响+KJNX3;P^ynq8C]Kzu。

When the rays of sunlight enter the atmosphere,the atmosphere tends to deflect the light from its straight-line path from the sun to the earth, and spread it around the sky, a process that is called scattering.
当太阳光线进入到大气层时，大气层会使阳光直行进入的路线产生偏离，并使光线散布于天空中，这个过程就叫做散射Nz3+-jH(7-b-Lfss9Mo。
If all the colors were spread equally the sky would look white, since all of the colors of light combined make white light.
如果所有颜色的光线都均匀分散开来，那么天空看上去就会是白色的，因为所有颜色的光线组合起来就是白光bb9@6MgUk.PcUb.[3t。
But the atmosphere does not spread all colors equally in all parts of the sky, and that is why the sky is not a uniform color.
但是大气层不会把所有颜色的光线均匀分布在整个天空中，这就是为什么天空看上去不是统一的颜色的原因mH6W+M|w7O_Y。
The color that is most readily spread is blue.
最容易发生散射的是蓝色的光ZKnog~E.#PI(IR。
So when we look up on a clear day we see blue sky,since the sunlight has had to pass through the least atmosphere, and fewer of the other colors of light have been spread.
由于阳光能够穿透最薄的大气层，并且只有少量颜色的光会发生散射，因此在晴朗的天气里，我们看到天空呈现出的就是蓝色5CB**.M*._9o。
However, closer to the horizon the sunlight must pass through more of the atmosphere before it reaches our eyes.
然而，在越靠近地平线的地方，阳光在进入我们的视野之前必须要穿过的大气层也就越厚4i,m|^2-N08)。
This gives the rays of other colors of light a chance to be spread so that the light reaching our eyes is more a mixture of all the colors and therefore appears lighter.
这就为其他颜色的光发生散射提供了机会e*.rU@FmXf@cVg。这样一来，进入我们视线的阳光就更像是所有颜色的光的混合体，因此会看上去会比较浅一些Vy=q^BEhpKQ|ZLE。