十万个为什么·科学启蒙30篇（1）

1 / 30

天空为什么是蓝色的？

Sunlight looks white, but it actually contains all colors of the rainbow mixed together.
When sunlight enters Earth’s atmosphere, tiny air molecules scatter the light in all directions.
Blue light has shorter wavelengths and scatters much more easily than red or yellow light.
This strong scattering makes blue light reach our eyes from many different angles across the sky.
At sunrise or sunset, sunlight travels through more atmosphere, so most blue light is scattered away.
The remaining light that reaches us directly is richer in red and orange wavelengths instead.
That’s why the sky near the sun appears golden or fiery during those times.
Without an atmosphere—like on the Moon—the sky would always look black, even at noon.
Scientists use this same scattering principle to study the composition of distant planetary atmospheres.
You can even see a hint of this effect by shining a flashlight through a glass of water with a drop of milk.