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天空的颜色是怎么形成的?

Why is the Sky Any Color?

“为什么天空是蓝色的?”
“Why is the sky blue”?
这个问题听起来和时间一样古老了,但是它也没有那么古老。
It sounds like a question that’s as old as time, but it isn’t that old at all.
当古希腊诗人荷马写《奥德赛》和《伊里亚特》这两部史诗的时候,他没有用过一次“blue”这个单词
When the Greek poet Homer wrote the Odyssey and the Iliad, he never once used a word for “blue”.
从希腊到非洲再到中国,蓝色成为语言想要用的最后颜色之一。
From Greece to Africa to China, blue turns out to be one of the last colors
长期以来,很多人认为天空和海洋都是蓝色的原因是一样的:
that languages figure out a word for. For a long time, many people thought that the sky was blue for the same reason the ocean is blue:
空气,就像水一样,是非常微弱的蓝色,所以尽管少量的话似乎是无色的,
Air, like water,is only very faintly colored blue. So though a small amount appears to be colorless, an
海洋,湖泊,天空,自然看起来是深蓝色。当然,那是完全错误的,
ocean, lake, or the sky naturally looks deep blue. Of course, that’s COMPLETELY wrong,
天空并不总是蓝色的,对吗?特别是在一天的的开始和结束的时候更是这样。
and the sky isn’t even always blue, right? At the beginning and end of the day, it looks
是红色或橙色。所以我们现在有两个问题:天空为什么是蓝的,天空又为什么是红的?
red or orange. So now we have two questions: Why is the sky blue, and also why is the sky
结果证明是,天空之所以是红的是因为天空是蓝的。让我解释给你们看为什么
red? It turns out, the sky is red BECAUSE the sky is blue. Let’s me show you why that
是这样
is.
下午3点,你在晴朗的加利福尼亚的海滩上,抬头凝望着蓝天。在下午2:52,
It’s 3 PM and you’re on a beach in sunny California, staring up at a blue sky. At 2:52
仅仅八分钟之前,一束光离开太阳旅行到了地球
PM, just eight minutes before, a beam of light left the sun traveling to Earth at just under
以每秒300百万米(30万千米)的速度,携带着从x射线到无线电波所有波长的光,
300 million meters per second, carrying every wavelength from x-rays to radio waves on their
花费了八分钟旅程到达地球。
eight minute trip to Earth.
在下午3点之前,不到一毫秒的时间内,这束在你之上的光穿过大气层。
Less than a millisecond before 3 PM, high above you, that beam of light enters Earth’s
在穿过大气层的路途上,阳光会衰减到
atmosphere. On its way through the atmosphere, that sunbeam will be trimmed down to just
窄波段
a narrow range of wavelengths.
但这束光仍然呈现白色,所有波长的混合。
But that light still appears white, a mixture of all wavelengths. Here’s where it gets
一个叫John Strutt的物理学家,了解到空气微粒能散射光
cool. A physicist named John Strutt, figured out that air molecules can actually scatter
当它穿越大气层。它们的散射多少决定于
light as it travels through the atmosphere. It turns out that how much they scatter depends
波长的四次方幂分之一。这意味着短波如蓝色和
on one over the 4th power of the wavelength. That means short wavelengths like blue and
蓝紫色比长波像红色和橙色散射更多
violet get scattered more than long wavelengths like red and orange.
其中一些蓝色和蓝紫色光散射进入你的眼睛。它们混合着一些白光,
Some of those blues and violets scatter down into your eyes. They get mixed with some white
你看到的颜色看起来非常像这个。但蓝紫色光
light, and you end up seeing a color that looks a lot like this. But violet light has
甚至比蓝光波长更短。所以为什么天空不是蓝紫色呢?那是因为
an even shorter wavelength than blue, so why isn’t the sky violet? That’s because the
你的眼睛感受器进化到蓝光比蓝紫光更敏感
color receptors in your eyes have evolved to be more sensitive to blue than violet.
现在是3:01,当你忙于思考紫色天空时,你的电话响了
By now it’s 3:01, and while you’re busy thinking about purple skies, your phone rings.
是你的朋友从百慕大群沙滩上打来的,比你看到日落
It’s your friend calling on the beach in Bermuda, watching the sun set four hours ahead
提前4个小时
of you.
那些颜色的结果都是和天空蓝色相同的原理
Those colors are a result of the same science that makes the sky blue. When the sun is just
在地平线之上,日出和日落的光穿过更厚的大气
above the horizon, the light in a sunrise or sunset has to travel through more atmosphere
比在任何时候都多。所有没被散射的是
than at any other time. All that’s left, all that DOESN’T get scattered, are the
这些最长的波段:红色,橙色,黄色。 蓝色缺失了吗?
longest wavelengths: red, orange, yellow. The blue that’s missing? That’s the blue
你看到的蓝色,万里之遥呢。
that you see, thousands of miles away.
他们说:“愿你在此!” 在某种程度上,你是。
They say: “Wish you were here!” and in a way, you are. You’re each looking at different
你们各自看到的是相同阳光的不同波段。
pieces of the same sunbeam.

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