秋天的天空為什么這么藍?

秋天的天空為什么這么藍?

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.

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

“為什么天是藍色的?”這是好奇的孩子們最常提出的一個經典問題，與宇宙中的其他許多重大謎團不同，多虧了一位名叫約翰·威廉·斯特拉特的先生，我們知道了這個問題的答案。這位19世紀的物理學家因發(fā)現(xiàn)氬氣元素而在1904年獲得了諾貝爾獎，但真正鞏固了斯特拉特在歷史書中的地位的是他對瑞利散射的發(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.

讓我們來了解一下藍天是如何形成的:來自太陽的光是由多種顏色組成的，它們以不同的波長表現(xiàn)出來。例如，紅光的波長最長，而在光譜的另一端，紫光和藍光的波長最短。當光線穿過地球的大氣層時，會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，這就是為什么藍光和紫光更容易散射的原因。結果就形成了我們美麗的藍天。

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色的天空，但實際上它是紫色的。我們之所以認為天空是藍色的，而不是紫色的，是因為我們眼睛的生理機能對藍色更敏感。

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色的，是時候回到最初的問題了——為什么隨著秋天的深入天空會顯得格外藍?這有幾個原因。

The sun is positioned lower in the sky.

太陽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，太陽穿過天空的路徑在地平線上下降。這增加了到達地球表面我們眼睛的散射藍光的數(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錄，秋天帶來的季節(jié)性緩解令人欣慰。不僅溫度更溫和，而且整體濕度也更低。因為空氣中沒有那么多的水分，云層就不會那么容易形成，霧霾也不會阻塞我們的城市中心。這樣就可以清晰地看到上面蔚藍的天空。

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

秋葉的暖色調與藍天相得益彰。

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.

如果你曾經在藝術課上做過色輪，你就會知道藍色和橙色是互補色。秋天的金色、橙色和紅色的樹葉在已經燦爛湛藍的天空的映襯下，顯得格外美麗。