Name: 為什麼有些彩虹會變白 (Why Some Rainbows Turn White)
Uploaded: 2025-10-25T18:39:53.000Z
Duration: 4 min 17 s

基礎被動語態

When I took this photo, I didn't know what I was looking at.

我拍這張照片的時候，還不知道那是什麼。

It seemed like a rainbow, except with all of its color drained away like a shadow or a ghost.

看起來像彩虹，但顏色都褪光了，像陰影或鬼魂一樣。

Ghost rainbows like this are technically called fog bows.

這種鬼魂彩虹，技術上稱為霧虹。

And fog bows form in almost the exact same way as regular rainbows, except for one key.

霧虹的形成方式和一般彩虹幾乎一樣，只有一個關鍵不同。

No, it's actually that the water droplets are around 10 to 100 or more times smaller than those in a rainbow.

不，其實是因為水滴比彩虹裡的水滴小了大概 10 到 100 倍或更多。

And that's what makes all the diffraction, I mean all the difference.

這就是造成所有繞射，我是說所有差異的原因。

So let's get into how smaller droplets remove the color from a rainbow.

所以，我們來看看小水滴是如何讓彩虹失去顏色的。

There are some great in depth explanations for rainbows, so we won't get into the details here, but

關於彩虹的深入解釋有很多，我們這裡就不詳述了，

the relevant summary is when sunlight strikes a drop of water, some of it reflects backwards off the insides of the drop at a bunch of angles, but

但重點是當陽光照射到水滴時，一部分會從水滴內部以許多角度反射回來，

其中大約在 140 度時反射最為明亮。

The exact angle depends on the color, with bluer light bending the most and ending up closest to 140 degrees, while redder light bends the least.

確切的角度取決於顏色，藍光彎曲最多，最接近 140 度，而紅光彎曲最少。

The result is that white light gets spread out into a rainbow like spectrum of colors when it reflects off the inside of a raindrop.

結果就是，當白光從雨滴內部反射時，會散開成彩虹般的色譜。

So if you look up at the sky at a collection of drops, when you look up at an angle of 42 degrees relative to the direction of the sun, you'll see redder light coming from those drops.

所以，如果你抬頭看天空中的水滴集合，當你相對於太陽方向看 42 度時，你會看到來自那些水滴的紅光。

And when you look at 40 degrees relative to the sun, you'll see bluer light with other rainbow colors coming from drops in between.

而當你相對於太陽看 40 度時，你會看到來自中間水滴的藍光和其他彩虹顏色。

這樣，一個漂亮的彩虹就出現了。

waves can interfere with each other and themselves, which messes up the perfect light rate picture we just presented.

波會互相干涉，也會自我干涉，這會破壞我們剛才呈現的完美光線圖像。

In the case of the reflected light from a raindrop, the physics is similar to what happens when you shine a light through a slit, since a reflection off of a small object isn't that different than sending light through an opening the size of the object from the opposite direction.

所以，從雨滴反射的光線，其物理原理跟用光線照射狹縫時發生的情況很像，因為從一個小物體反射，跟從相反方向將光線送入該物體大小的開口，其實差別不大。

With a slit, interference happens because waves passing through different parts of the slit alternately add up or cancel out and create what's called a diffraction pattern of bright and dark spots.

在狹縫的情況下，干涉會發生，因為通過狹縫不同部分的波會交替地相加或相消，並產生所謂的繞射圖案，也就是明暗斑點。

And with a small object, it's the reflections off the different parts of the object that add up and cancel out.

而對於小物體來說，是從物體不同部分的反射相加和相消。

The effect on rainbows is that instead of a drop just reflecting back bright light at around 140 degrees, there are a bunch more bright reflections at more extreme angles.

這對彩虹的影響是，一個水滴不只會在約 140 度反射出明亮的光線，還會在更極端的角度出現更多明亮的反射。

And this means that each color doesn't just appear as a single ring, but

這表示每種顏色不只會出現一個單一的圓環，

instead a bright outer ring and a progressively fainter series of concentric inner rings.

而是出現一個明亮的外部圓環，以及一連串逐漸變暗的同心內部圓環。

The reason we don't see concentric rainbows is because of a key property of diffraction patterns.

我們之所以看不到同心的彩虹，是因為繞射圖案有一個關鍵特性。

A wide slit will have lots of narrow, closely spaced bright spots, while a narrow slit will have wider, farther apart peaks.

寬的狹縫會有許多狹窄、緊密排列的亮點，而窄的狹縫則會有較寬、間隔較遠的峰值。

The narrower the slit, the broader the diffraction pattern.

The wider the slit, the tighter the pattern.

And the raindrops in normal rainbows are the equivalent of very wide slits.

而正常彩虹中的水滴，就相當於非常寬的狹縫。

For a rainbow formed from raindrops a millimeter or larger in size, the diffraction pattern is so narrow that the effects of diffraction are essentially absent and you get the crisp, high contrast stereotypical rainbow.

對於由一毫米或更大的水滴形成的彩虹，繞射圖案非常窄，繞射效應幾乎不存在，你會得到清晰、高對比度的典型彩虹。

But for drops a bit smaller than a millimeter, the diffraction pattern creates concentric rings for each color that are far enough apart to create extra repeating colored arcs on the inside of the original rainbow.

但對於比一毫米稍小的水滴，繞射圖案會為每種顏色產生同心圓環，這些圓環彼此間隔足夠遠，會在原始彩虹的內側產生額外的重複彩色弧。

These are so called supernumerary bows with even smaller water droplets.

這些就是所謂的副虹，是由更小的水滴形成的。

Around a twentieth of a millimeter, the rainbow and supernumerary bows get even broader and even farther apart.

大約二十分之一毫米時，彩虹和副虹會變得更寬，間隔也更遠。

But crucially, different colors of light are still only bent away from each other by the same amount as before.

但關鍵是，不同顏色的光仍然只會以和之前相同的量彎曲。

And so the broadening of the rings causes colors to blur into each other, making the rainbow less vivid.

是以，圓環的變寬會導致顏色互相模糊，使得彩虹的鮮豔度降低。

Eventually, with super small water droplets a few hundredths of a millimeter like you get in fog, diffraction causes all the individual colors to broaden out so much, they pretty much completely overlap and add back up to the same original color of sunlight as they started white light.

最終，對於像霧中那樣幾百分之一毫米的超小水滴，繞射會使所有單獨的顏色擴展得如此之多，以至於它們幾乎完全重疊，並加回到最初的陽光顏色，就像它們最初是白光一樣。

You can see the same thing happen if you look at red, green and blue colors through an out of focus, they blur together into white.

如果你透過失焦的狀態看紅色、綠色和藍色，它們會模糊地融合成白色，你會看到同樣的情況發生。

A fogbow is still basically a rainbow caused by the same physics, but

霧虹基本上是由相同的物理原理造成的彩虹，但是

it's one that's had the color blurred out of it by diffraction from the tiny fog droplets.

它是因為微小水滴的繞射而讓顏色變得模糊的。

if you take just a single slice from a rainbow and plot how the rainbow changes as the water drop size gets smaller, you get a really cool diagram.

如果你從彩虹中取一小段，然後繪製出彩虹隨著水滴大小變小而變化的圖，你會得到一張很酷的圖表。

On one end we have slices corresponding to the purest colored rainbows, and

on the other end, slices corresponding to pure white fog bows with all the other varieties of rainbows with supernumerary bows in between.

另一端則是純白霧虹，中間則是各種不同種類的彩虹，帶有額外的彩虹。

Which brings us to today's sponsor Opera.

這就帶我們來到了今天的贊助商 Opera。

When I first saw this phenomenon years ago out on a walk, I was baffled and had to scour the Internet to figure out what it was.

多年前我第一次在散步時看到這種現象，我感到很困惑，不得不上網搜尋才弄清楚是什麼。

If instead I could have uploaded the photo to Opera's image recognition tool, I would have immediately seen that it was a fogbow and gotten a quick overview right there, as well as a deep dive via the links provided.

如果我能將照片上傳到 Opera 的圖像辨識工具，我會立刻知道這是一道霧虹，並在那裡得到一個快速的概覽，以及透過提供的連結進行深入瞭解。

Deep Diving is also assisted by Opera's tab islands.

Opera 的分頁群組也能幫助你深入研究。

searches into separate tab islands, keeping everything organized while still leaving space for your email and tab traces.

搜尋整齊地分類到不同的分頁群組，讓一切井然有序，同時也為你的電子郵件和分頁記錄保留空間。

Keep track of where you've been most recently.

The darker the underscore, the more recent the visit, so you can more easily keep track of the tab you were just on.

底線越深，代表造訪時間越近，這樣你就能更容易追蹤你剛才所在的分頁。

Plus, Opera's Pop Out Video Player lets you watch videos while you browse, which is great for following along with tutorials or how to videos.

此外，Opera 的 Pop Out Video Player 讓你可以在瀏覽網頁時觀看影片，這對於跟隨教學或操作說明影片非常實用。

So if you're inquisitive, creative, or love to multitask, then try Opera.

所以，如果你充滿好奇心、富有創意，或喜歡多工處理，那就試試 Opera 吧。

You may discover a new essential tool for web browsing.

你可能會發現一個全新的網路瀏覽必備工具。

Download it now for free via the link in the description.

立即透過說明中的連結免費下載。