One of the most striking properties about life is that it has color.
生命最令人瞩目的一个特性就是有颜色。
To understand the phenomenon of color, it helps to think about light as a wave.
为了理解颜色现象，我们需要将光想象成波。
But, before we get to that, let's talk a little bit about waves in general.
但在这一步之前，我们先来大体谈谈波。
Imagine you're sitting on a boat on the ocean watching a cork bob up and down in the water.
想象自己坐在海上的一只小船上，一个酒瓶塞随着水波上下飘动。
The first thing you notice about the motion is that it repeats itself.
你首先注意到的它重复的动向。
The cork traces the same path over and over again... up and down, up and down.
瓶塞沿着相同的路径上上下下。
This repetitive or periodic motion is characteristic of waves.
这种重复周期性的运动就是波浪的特点。
Then you notice something else... using a stopwatch,
然后你会注意到其他事，你可以用秒表
you measure the time it takes for the piece of cork to go over its highest position down to its lowest and then back up again.
计量出瓶塞从最高点到最低点、然后再回到最高点所用的时间。
Suppose this takes two seconds. To use the physics jargon, you've measured the period of the waves that cork is bobbing on.
假设耗时两秒。换成物理术语，你已经测出让瓶塞漂动的波浪的周期。
That is, how long it takes a wave to go through its full range of motion once.
这是指波完成一整个运动所耗的时间。
The same information can be expressed in a different way by calculating the wave's frequency.
这还可以用另一种方式表示--计算波的频率。
Frequency, as the name suggest, tells you how frequent the waves are.
频率，顾名思义，指波浪有多频繁。
That is, how many of them go by in one second.
也就是说，一秒钟有多少波浪产生。
If you know how many seconds one full wave takes, then it's easy to work out how many waves go by in one second.
如果你知道完整的波所花的时间，很容易就能算出一秒钟产生了多少波。
In this case, since each wave takes 2 seconds, the frequency is 0.5 waves per second.
在这里，每个波耗时2秒，频率就是0.5个波每秒。

So enough about bobbing corks... what about light and color?
说了这么多波动的瓶塞，光和颜色又是怎么回事呢？
If light is a wave, then it must have a frequency. Right? Well... yes, it does.
如果光是一种波，那它也会有频率，是吧？没错，它有频率。
And it turns out that we already have a name for the frequency of the light that our eyes detect. It's called color.
我们已经赋予眼睛所见光频一个名字了。那就是颜色。
That's right. Color is nothing more than a measure of how quickly the light waves are waving.
没错，颜色就是光波波动的频率。
If our eyes were quick enough, we might be able to observe this periodic motion directly, like we can with the cork and the ocean.
如果眼睛赶得上光速，我们也许能直接看到波动的周期，就和看海里的瓶塞一样。
But the frequency of the light we see is so high,
但是我们能看见的光频太高了，
it waves up and down about 400 million million times a second, that we can't possibly see it as a wave.
它每秒上下波动4万亿次，我们无法以波的形式看到。
But we can tell, by looking at its color, what its frequency is.
但是我们可以通过它的颜色来知道其频率。
The lowest frequency light that we can see is red and the highest frequency is purple.
肉眼可见的最低频光是红色的，最高频是紫色的。
In between all the other frequencies form a continous band of color, called the visible spectrum.
在这二者之间，其他频率形成连续的颜色波段，称为可见光谱。
So, what if you had a yellow pencil sitting on your desk?
桌子上有一支黄铅笔会发生什么？
Well, the sun emits all colors of light, so light of all colors is hitting your pencil.
太阳射出的光包含所有颜色，所有的颜色都照在铅笔上。
The pencil looks yellow because it reflects yellow light more than it reflects the other colors.
铅笔看起来是黄色的，因为它反射黄色的光比其他颜色要多。
What happens to the blue, purple and red light?
那蓝光、紫光、红光哪儿去了呢？
They get absorbed and the energy they are carrying is turned into heat. It is similar with objects of other colors.
它们都被吸收了，携带的能量转化成热量。其他颜色的东西都是如此。
Blue things reflect blue light, red things reflect red light and so on.
蓝色的反射蓝光，红色的反射红光，以此类推。
White objects reflect all colors of light, while black things do exactly the opposite and absorb at all frequencies.
白色的东西反射所有的光，黑色的则完全相反，吸收所有频率的光。
This - by the way - is why it's uncomfortable to wear your favorite Metallica t-shirt on a sunny day.
这就是为什么在艳阳天，穿你最喜欢的金属乐队T恤会不舒服。