秋天的天空為什么這么藍(lán)?

秋天的天空為什么這么藍(lán)?

The color of the leaves isn't the only thing that changes in autumn. Have you ever looked up on a crisp fall day and noticed how brilliant and clear the blue sky is? That's not just your imagination — the sky really is more blue, and all because of science.

樹(shù)葉的顏色并不是秋天唯一會(huì)改變的東西。你是否曾在秋高氣爽的時(shí)候抬頭仰望，發(fā)現(xiàn)湛藍(lán)的天空是如此的明亮和清澈?這不僅僅是你的想象——天空真的更藍(lán)了，這是有科學(xué)依據(jù)的。

To understand why the sky is so especially vivid in autumn, you first need to understand why it's blue in the first place.

要理解為什么秋天的天空如此鮮艷，你首先需要理解為什么它是藍(lán)色的。

Autumn color surrounds a pagoda in Fujiyoshida, Japan as Mount Fuji looms in the distance. (Photo: lkunl/Shutterstock)

"Why is the sky blue?" is a classic query posed most often by curious young children, and unlike the many other grand mysteries of our universe, we know the answer to this one, thanks to a gentleman named John William Strutt. This 19th-century physicist won a Nobel Prize in 1904 for discovering the element argon, but what really cemented Strutt's place in the history books is his discovery of Rayleigh scattering. Named for Strutt's inherited status as the third Baron of Rayleigh, this phenomenon explains how light scatters into different colors based on the molecular contents of the atmosphere.

“為什么天是藍(lán)色的?”這是好奇的孩子們最常提出的一個(gè)經(jīng)典問(wèn)題，與宇宙中的其他許多重大謎團(tuán)不同，多虧了一位名叫約翰·威廉·斯特拉特的先生，我們知道了這個(gè)問(wèn)題的答案。這位19世紀(jì)的物理學(xué)家因發(fā)現(xiàn)氬氣元素而在1904年獲得了諾貝爾獎(jiǎng)，但真正鞏固了斯特拉特在歷史書(shū)中的地位的是他對(duì)瑞利散射的發(fā)現(xiàn)。這一現(xiàn)象以斯特拉特繼承的瑞利第三男爵的身份命名，解釋了光線如何根據(jù)大氣中的分子成分散射成不同的顏色。

Let's go over the basics of how blue skies work: Light from the sun is made up of many colors, which manifest in different wavelengths. For example, red light has the longest wavelength and, on the other end of the spectrum, violet and blue light have the shortest wavelengths. When light passes through the Earth's atmosphere, it comes up against thick layers of gas molecules and dust particles. These tiny atmospheric bits are closer in size to shorter wavelengths, which is why blue and violet light scatter more easily. The result is our beautiful blue sky.

讓我們來(lái)了解一下藍(lán)天是如何形成的:來(lái)自太陽(yáng)的光是由多種顏色組成的，它們以不同的波長(zhǎng)表現(xiàn)出來(lái)。例如，紅光的波長(zhǎng)最長(zhǎng)，而在光譜的另一端，紫光和藍(lán)光的波長(zhǎng)最短。當(dāng)光線穿過(guò)地球的大氣層時(shí)，會(huì)碰到厚厚的氣體分子和塵埃顆粒層。這些大氣中的微小粒子在大小上更接近短波長(zhǎng)，這就是為什么藍(lán)光和紫光更容易散射的原因。結(jié)果就形成了我們美麗的藍(lán)天。

But wait! It's important to mention that although we see a blue sky, the truth is that it's actually violet. The reason we perceive the sky as blue instead of violet is due to the physiology of our eyes, which are more sensitive to blue.

但是等等!值得一提的是，雖然我們看到的是藍(lán)色的天空，但實(shí)際上它是紫色的。我們之所以認(rèn)為天空是藍(lán)色的，而不是紫色的，是因?yàn)槲覀冄劬Φ纳頇C(jī)能對(duì)藍(lán)色更敏感。

Yellow and orange autumn leaves contrast against a bright blue sky. (Photo: nohanka/Shutterstock)

So now that we know why the sky is blue, it's time to go back to the original question — why does the sky appear extra blue as we descend deeper into autumn? There are several reasons for this.

所以現(xiàn)在我們知道了天空為什么是藍(lán)色的，是時(shí)候回到最初的問(wèn)題了——為什么隨著秋天的深入天空會(huì)顯得格外藍(lán)?這有幾個(gè)原因。

The sun is positioned lower in the sky.

太陽(yáng)在天空中的位置較低。

As the days get shorter, the sun's path across the sky sinks lower to the horizon. This bumps up the amount of scattered blue light that reaches our eyes on the planet's surface.

隨著白天變短，太陽(yáng)穿過(guò)天空的路徑在地平線上下降。這增加了到達(dá)地球表面我們眼睛的散射藍(lán)光的數(shù)量。

Less humidity means less haze and clouds.

濕度越低，霾和云就越少。

As our summers continue to break soaring temperature records, there's something so comforting about the seasonal reprieve that autumn brings. Not only are temperatures milder, there's also less humidity across the board. Since the air isn't holding as much moisture, clouds don't form as easily and haze doesn't clog our urban centers. The result is a crystal clear view of the azure expanse above.

隨著夏季氣溫不斷刷新紀(jì)錄，秋天帶來(lái)的季節(jié)性緩解令人欣慰。不僅溫度更溫和，而且整體濕度也更低。因?yàn)榭諝庵袥](méi)有那么多的水分，云層就不會(huì)那么容易形成，霧霾也不會(huì)阻塞我們的城市中心。這樣就可以清晰地看到上面蔚藍(lán)的天空。

The warm hues of fall foliage naturally complement the blue sky.

秋葉的暖色調(diào)與藍(lán)天相得益彰。

Clear autumn skies over Lake Millstatt in Austria. (Photo: Yauheni_M/Shutterstock)

If you've ever made a color wheel for an art class, you'll know that blues and oranges are complementary colors. As direct "opposites" of each other, the gold, orange and red leaves of autumn pop beautifully against the already brilliant blue sky.

如果你曾經(jīng)在藝術(shù)課上做過(guò)色輪，你就會(huì)知道藍(lán)色和橙色是互補(bǔ)色。秋天的金色、橙色和紅色的樹(shù)葉在已經(jīng)燦爛湛藍(lán)的天空的映襯下，顯得格外美麗。