『小方糖日記簿』

小軒看著快下雨的天空問我，Why are rainy clouds dark?
我說因爲裏面有很多的水份啊~~他問爲何很多水分就會變灰色？
我不知道怎樣回答。
原來是因爲很多水分，所以導致光線透不過去。
在這裡找到答案。


The main reason why rain clouds are dark is due to their particulate density. As clouds are formed from minuscule water droplets and/or ice crystals, the denser they are packed, the more light radiating from the Sun is scattered and dispersed by them, lending a darker appearance to their lower sections.

This is best visualised by a trip on an aeroplane, with clouds on an overcast day seeming grey/black in colour when viewed on the runway, yet a bright white when viewed from above during flight. Essentially, the deeper and denser a cloud formation is, the less light will pass through it.

FROM http://www.howitworksdaily.com/environment/why-are-rain-clouds-dark/