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Why The Sky Is Not Blue
為什么天空不是統一的藍色
Look at various parts of the sky on a clear day and you will see that it is not a uniform blue. Even if the sky is deep blue when you look straight up, near the horizon it is lighter.
抬頭仰望天空，你會發現在晴朗的日子里，天空并不會呈現出統一的藍色。即使你頭頂上正對的這片天是深藍色的，靠近地平線處的也會相對較淺一些。
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. 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.
部分原因要歸咎于污染，但是就算是在最干凈的空氣中，貼近地平線處的天空顏色也會比較淺，這是由于地球大氣層對陽光的影響。當太陽光線進入到大氣層時，大氣層會使陽光直行進入的路線產生偏離，并使光線散布于天空中，這個過程就叫做散射。
If all the colors were spread equally the sky would look white, since all of the colors of light combined make white light. 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.
如果所有顏色的光線都均勻分散開來，那么天空看上去就會是白色的，因為所有顏色的光線組合起來就是白光。但是大氣層不會把所有顏色的光線均勻分布在整個天空中，這就是為什么天空看上去不是統一的顏色的原因。
The color that is most readily spread is blue. 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.
最容易發生散射的是藍色的光。由于陽光能夠穿透最薄的大氣層，并且只有少量顏色的光會發生散射，因此在晴朗的天氣里，我們看到天空呈現出的就是藍色。
However, closer to the horizon the sunlight must pass through more of the atmosphere before it reaches our eyes. 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.
然而，在越靠近地平線的地方，陽光在進入我們的視野之前必須要穿過的大氣層也就越厚，這就為其他顏色的光發生散射提供了機會。這樣一來，進入我們視線的陽光就更像是所有顏色的光的混合體，因此會看上去會比較淺一些。
