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.
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Earth’s atmosphere scatters shorter blue and violet wavelengths far more than longer red and orange ones.
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During midday, sunlight travels a relatively short path through clean air, so blue dominates what reaches our eyes.
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At sunrise or sunset, light must pass through much more atmosphere, scattering away most blue and green light.
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Only longer wavelengths—red, orange, and pink—survive the long journey to our location.
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Dust, pollution, or volcanic ash can intensify reds by adding extra particles that scatter light even more.
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Pilots sometimes report vivid purple or magenta glows when high-altitude ice crystals refract scattered light uniquely.
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Astronauts see black space above Earth because there’s no atmosphere to scatter sunlight at all.