“天空为什么是蓝色的？”这个问题几乎困惑了我整个童年。父母不知道这个问题的答案。母亲在我的追问下，对我说：“妈妈不知道哦，你好好读书，以后学会了告诉妈妈好吗？”嗯，我有一个好妈妈。（喂，跑题了！）兴冲冲上学堂，结果书本上也没有教，又没胆去问老师，就这么不了了之了。童鞋们，你知道天空是什么颜色吗？
　　White light is made up of a mixture[混合] of different
　　colours. Light travels in waves， and different colours have different wavelengths[波长]. Things seem a particular colour because of the light they reflect[反射] or scatter[散射]—a leaf appears green because it reflects green light.
　　Scattering Light
　　Shine a torch[手电筒] through an empty glass or bottle
　　and look at the colour of the light in the bottle. Hold a piece of paper on the other side of the bottle and look at the colour of light that has passed through[通过]. Fill the glass or bottle with water and shine the torch through it. What colour is the light passing in the bottle or glass，and what colour is the light on the paper？ Add a drop or two of milk and mix it thoroughly[充分地]， and shine the torch through it again—what happens to the light in the glass or bottle， and the light on the paper？
　　Particles in suspension[悬浮] reflect light—
　　this is called the “Tyndall Effect” （think of how car headlights[车头灯] reflect off fog， which is a suspension of water droplets[微水滴] in air）.
　　Light travels directly through water， with little reflection and scattering， and the colour does not change. Milk in water is a suspension of fat and protein[蛋白质] particles[微粒] in water. The suspended particles should change the colour of the light in the bottle or glass to a bluish[带蓝色的] tinge[淡色]， with the light on the paper having a reddish[微红的] tinge.
　　The blue part of the light （shorter wavelength） from the torch should be reflected and scattered by the particles in the suspension， more than the red， orange and yellow parts of the light （longer wavelength）. When this scattered light reaches people’s eyes， it makes the mixture seem blue， particularly at the edges. The particles allow more of the red， orange and yellow light through， so the light on the paper will have more of these colours in it.
　　The light at the centre of the glass or bottle may also seem to have a reddish tinge—this is because it has passed through more particles than the light at the edges， so more of the blue light has been scattered away.
　　Blue Skies
　　Air molecules[微粒] also affect light. They absorb[吸收] the light and then release[释放] （scatter） it in another direction. This is called the “Rayleigh Effect”. Air molecules absorb and release blue light more often than red， orange and yellow light. As this light is scattered， it reaches people’s eyes， making the sky seem blue. The red， orange and yellow light carries straight on without being scattered by the air molecules， so people do not see as much of it.