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(Sci Show - Fast Fact)

(Sci Show - 快速小知識)

If you've ever paid close attention to the humidity levels on your phone's weather app, you might have noticed that they always seem to make no sense.

如果你曾經仔細關注過手機天氣預報 App 上的溼度，你可能已經發現它們似乎總是不太合理。

Like, in the summer, your app can say there's 75% humidity, and you'll be sticky and sweaty.

例如，在夏天，應用程式顯示濕度為 75% ，你會全身黏糊糊，還滿頭大汗。

But during winter, 75% might mean that your skin is super dry.

但在冬天，75% 的濕度可能意味著你的肌膚異常乾燥。

So, what's going on here?

那麼，為什麼會這樣呢？

Well, it turns out that the most common definition of humidity is kind of inconvenient.

事實證明，最常見的溼度定義其實不太便利。

But there is a better way to think about it.

但是有個更好的方法來考慮這個問題。

It all comes down to the fact that your phone, and most weather channels, specifically report relative humidity.

這一切都歸結於一個事實：你的手機和多數氣象頻道都會集中報導相對溼度。

This number is measured in percentages, and it's the amount of moisture in the air compared to how much water the air can hold.

這個數字是以百分比測量，指的是空氣中現有的水份與所能容納的水份相比。

And the key is: How much water the air can hold depends a lot on temperature.

而關鍵是：空氣中能容納多少水很大部份取決於溫度。

See, for water vapor to come out of the air, it has to go from a gas to a liquid, usually by condensing onto something like dust or your window glass.

水蒸氣要脫離空氣，得從氣體變成液體，通常是通過冷凝在灰塵或窗戶玻璃等物體上。

And for something to go from a gas to a liquid, it has to lose energy.

而一個物體要從氣體變成液體必須失去能量。

In other words, the molecules have to physically slow down.

換句話說，分子必須減緩物理速率。

Well, when the air is warm, the water molecules in it contain a lot of energy.

那麼，當空氣是溫暖的，其中的水分子會含有大量能量。

They're moving more than water molecules in cooler air.

比起在冷空氣中，水分子在暖空氣中運動的更頻繁。

That means they're less likely to condense out of the atmosphere, and they end up hanging out in the air and making things feel all sticky.

這意味著它們比較不會從大氣中凝結出來，而是會滯留在空氣中讓人感覺黏糊糊的。

So, temperature plays a big role in relative humidity.

是以，溫度對相對溼度有很大的影響。

And it's why this stat usually isn't that useful in planning your day.

這也是為什麼這個統計數字在你規劃日程時通常不太有用。

If it's -10 degrees Celsius, the air can't hold as much moisture, so 75% humidity isn't actually that humid.

加設氣溫是零下 10 攝氏度，這時空氣中無法容納那麼多水分，溼度 75% 實際上就不會那麼潮溼。

But if it's 20 degrees, 75% humidity suddenly means there's a lot more water in the air to make things feel all muggy.

但如果是 20 度，溼度 75% 突然就意味著空氣中有很多水份，會讓人感到很悶熱。

If you want a number for humidity that isn't quite so relative, try the dew point temperature.

如果你想要一個不那麼相對的溼度數字，試試露點溫度。

This is the temperature at which water droplets or dew form on things like grass.

這是水滴或露水在像草這樣的東西上形成的溫度。

In other words, it's the temperature at which the air is completely saturated with moisture.

換句話說，這是空氣中水份完全飽和的溫度。

And the closer the dew point temperature is to the temperature outside, the stickier and more unpleasant it'll be.

而露點溫度越接近外面的溫度，空氣就會越粘、越令人不舒服。

For reference, people react differently to dew points, but most folks are comfortable with a dew point of 10 degrees Celsius.

作為參考，人們對露點溫度的體感反應是不同的，但大多數人覺得 10 攝氏度的露點是舒服的。

And things get pretty humid and unpleasant around 15 or 21 degrees.

而在 15 到 21 度左右，則會感到相當潮溼、不適。

So, it's still a new scale to learn, but it's also consistent no matter how cold it is outside.

所以，這是個需要學習的新尺度，但它相當一致，無論氣溫如何。

Now, the big question is: If the dew point temperature is a great way to tell you how the outside world feels, why don't weather apps and weather channels use it?

現在，有個重要的問題是，如果露點溫度是告訴你外面世界體感的好方法，為什麼天氣預報 App 和氣象頻道不使用它呢？

It's mostly a matter of history.

這主要關乎歷史。

Instruments that measure relative humidity predate the ones that measure dew points.

測量相對溼度的儀器比測量露點的儀器更早出現。

Like one of the first mechanical hygrometers, a device that measures humidity, appeared in 1783.

比如，最早的機械式溼度計之一，這種設備可以測量溼度，出現在1783年。

And, since these devices were widely available to the public and gave reliable measurements of relative humidity, the term, unfortunately, stuck around.

由於這些設備被廣泛提供公眾使用，且其測量結果是可靠的，這個方法不幸的到現在一直為人所用。

You know what else is available to the public and gives reliable science inspiration?

知道還有什麼是公眾可取得，且能給予可靠的科學啟發嗎？

"music for scientists", a tribute album to science inspired by the beauty of science.

《科學家的音樂》，向科學的靈感致敬的專輯。

It was written and recorded by Patrick Olsen,

它由帕特里克-奧爾森編寫和錄製。

and if you want to check it out, I'd recommend starting off with the song "Aristarchus in the Rain", which isn't about humidity, but it is about a scientist trying to make sense of this messy and cloudy world.

如果想查看，我建議從《雨中亞里士多德》這首曲子開始，它跟溼度沒關係，而是講述一位科學家試圖瞭解這個混亂、多變世界的故事。

If you want to check it out, look for "music for scientists" on all major music streaming services or click the link below.

快搜尋《科學家的音樂》，所有主要音樂串流平台都可找到，也可點擊下面連結收聽。