I'm Ben, and here's today's question.

我是班，這邊是今天的問題。

Why is the sky blue?

為什麼天空是藍的？

This is one of those questions that four-year-olds ask all the time, and it's something interesting to think about.

這是那些我們在大約四歲的時候經常問的問題之一，也是值得思考的有趣問題。

So let's start here. When you look at the sky at night it's black, and there are stars, and there's the moon,

那麼，我們開始吧。當你在晚上看著天空時，它是黑的，還有一些星星和月亮，

and they form these points of light on that black background.

它們組成了黑夜背景上的光源。

So why is it that during the day the sky doesn't remain black with the sun acting like just another point of light?

那麼為什麼在白天裡，太陽就像另一個光源，但天空卻沒有維持黑暗？

I mean, that's exactly what happens on the moon.

我是說，月亮就是這樣啊。

So why on Earth-- huh, on Earth--does the daytime sky turn a bright blue,

所以為什麼在地球上，白天的天空變成亮藍色，

and all the stars except for the sun seem to disappear during the day?

而且除了太陽以外的其他星星都好像消失了？

There's a couple things we have to recognize.

有一些事我們必須要認識一下。

First, the sun is an extremely bright point of light. It's also much closer to Earth.

第一，太陽是一個非常亮的光源。它也很靠近地球。

The second thing to recognize is that the atoms and nitrogen

第二個要知道的是原子、氮氣，

and oxygen in the atmosphere havean effect on the sunlight that passes through them.

還有氧氣在大氣中會對穿透過它們的陽光起反應。

Also, there's scattering that causes light to scatter throughout the sky when it passes through particles

還有，當光穿透過這些粒子時會產生散射使光在天空中四處分散。

that have a diameter that's 1/10 that of the wavelength or the color of the light.

這些粒子只有色光或是波長直徑或色光直徑的十分之一。

Now, sunlight is made up of all different colors of light.

接著，陽光是由不同的色光所構成的。

But because of the elements in our atmosphere, the color blue is scattered much more efficiently than all of the other colors.

但是因為我們大氣中的元素，藍色比其他的顏色被更有效地分散出去。

So when you and I look at the sky on a clear day, we can see the sun as a bright disk.

所以當我和你在晴朗的某一天看著天空時，我們可以看到像明亮圓盤一樣的太陽。

And that blueness that we see everywhere else is all of the atoms in the atmosphere scattering blue light toward us.

而我們在其餘地方看到的藍色都是大氣裡的所有原子將藍色的光散射給我們的。

That's because red light, yellow light, green light,

那是因為紅光、黃光、綠光，

all of the other colors are not scattered nearly as well and we see the sky as blue as a result.

所有其他的顏色幾乎都沒有被散色，結果我們看見的天空就是藍色。

And that blue color is so bright that it completely blots out all the other stars because they're so dim in comparison.

加上藍色很亮，完全將其他星星遮住了，因為相較之下它們比較黯淡。

So that's it. That is why the sky is blue.

就是這樣！這就是為什麼天空是藍的。

Thanks so much for watching.

非常感謝你的觀看。

We hope you enjoyed this episode.

我們希望你喜歡這一集。

And as always, you know what I'll say at this point.

一如往常，你知道我會說的

Do you want to comment?

想要給點意見嗎？

We have a comment section.

我們有個意見欄！

Do you want to like?

喜歡嗎？

We have a button for that, and subscribe as well.

我們有按鍵可以訂閱！

These videos are cool.

這些影片很酷！

These videos are cool.

這些影片很酷！

You know, I feel safe saying that all three of these videos

我必須要說這些影片，

are cool.

都很酷！