十万个为什么·科学阅读30篇（1）
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Why Is the Sky Blue During the Day But Red at Sunset?
为什么白天天空是蓝色，日落时却变红？
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Sunlight appears white but contains all visible colors, each traveling as a different wavelength.阳光看似白色，实则包含所有可见光色，每种颜色对应不同波长。
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Earth’s atmosphere scatters shorter blue and violet wavelengths far more than longer red and orange ones.地球大气对较短的蓝光和紫光散射远强于较长的红光和橙光。
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During midday, sunlight travels a relatively short path through clean air, so blue dominates what reaches our eyes.正午时，阳光穿过洁净空气的路径较短，因此蓝光主导了到达我们眼睛的光线。
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At sunrise or sunset, light must pass through much more atmosphere, scattering away most blue and green light.日出或日落时，阳光需穿过更厚的大气层，大部分蓝光和绿光被散射殆尽。
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Only longer wavelengths—red, orange, and pink—survive the long journey to our location.仅有波长较长的红、橙、粉色光能穿越漫长路径抵达我们所在位置。
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Dust, pollution, or volcanic ash can intensify reds by adding extra particles that scatter light even more.尘埃、污染物或火山灰可增加散射粒子，进一步增强红色调。
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Pilots sometimes report vivid purple or magenta glows when high-altitude ice crystals refract scattered light uniquely.飞行员有时在高空报告看到鲜明的紫色或洋红色辉光，这是高空气冰晶对散射光的独特折射所致。
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Astronauts see black space above Earth because there’s no atmosphere to scatter sunlight at all.宇航员看到地球上方是黑色太空，因为那里没有大气散射阳光。