閏年並不是每四年一次：英語精讀講義

A calendar year is made of 365 days, 片語搭配

一個日曆年由365天組成，

a number that refuses to be divided nicely, 慣用語

這個數字無法被整除，

which is why we end up with uneven months of either 30 or 31 days, 講解

這就是為什麼我們最後會得到30天或31天的不均勻月份，

except for February, the runt of the litter, 慣用語

除了二月，這個月像是發育不良的小個子，

which gets only 28,

只有28天，

except when it gets 29,

除非它有29天，

and then the year is 366 days long.

那樣的話這一年就有366天。

Why does that happen?

為什麼會這樣呢？

What kind of crazy universe do we live in where some years are longer than others? 表達脈絡

我們究竟生活在怎樣一個瘋狂的宇宙裡，有些年份居然比其他的要長？

To answer this,

要回答這個問題，

we need to know just what is a year.

我們需要知道究竟什麼是一年。

Way oversimplifying it, 表達脈絡

極度簡化地說，

a year is the time it takes the Earth to make one trip around the Sun. 文法

一年就是地球繞太陽轉一圈所需的時間。

This happens to line up with the cycle of the seasons. 講解

這剛好與四季的輪迴相吻合。

Now, drawing a little diagram like this showing the Earth jauntily going around the Sun is easy to do, 文法

那麼，畫一張像這樣展示地球輕快地繞著太陽轉的示意圖很容易，

but accurately tracking a year is tricky when you're on Earth because the universe doesn't provide an overhead map.

但在地球上準確追蹤一年卻很棘手，因為宇宙不提供俯瞰圖。

On Earth, you only get to see the seasons change, 文法

在地球上，你只能看到四季更迭，

and the obvious way to keep track of their comings and goings is to count the days passing, 講解

而記錄四季變遷的顯而易見的方法就是計算流逝的天數，

which gives you a 365 day calendar.

這樣你就有了個365天的日曆。

But as soon as you start to use that calendar, 文法

但一旦你開始使用這個日曆，

it slowly gets out of sync with the seasons, 片語搭配

它就會慢慢與四季脫節，

and with each passing year, 片語搭配

隨著時間流逝，

the gap gets bigger and bigger and bigger. 文法

差距會變得越來越大。

In three decades,

三十年後，

the calendar will be off by a week, 用詞

日曆就會偏差一個星期，

and in a few hundred years,

而幾百年後，

the seasons would be flipped,

四季就會完全顛倒，

meaning Christmas celebrations taking place in summer,

意味著聖誕慶祝活動會在夏天舉行，

which would be crazy.

這簡直太瘋狂了。

Why does this happen?

為什麼會發生這種情況？

Did we count the days wrong?

是我們算錯天數了嗎？

Well,

其實，

the calendar predicts that the time it takes for the Earth to go around the Sun is 8,760 hours,

日曆預測地球繞太陽轉一圈所需的時間是8760小時，

but if you actually timed it with a stopwatch, 文法

但如果你真的用碼表去計時，

you'd see that a year is really longer than the calendar predicts by almost six hours. 文法

你會發現一年實際上比日曆預測的時間長了近六個小時。

So our calendar is moving ever so slightly faster than the seasons actually change. 片語搭配

所以我們的日曆走得比季節的實際更迭稍微快了一點點。

And thus we come to the fundamental problem of all calendars. 表達脈絡

於是我們來到了所有日曆的根本問題。

The day-night cycle,

晝夜交替，

while easy to count, 文法

雖然容易計算，

has nothing to do with the yearly cycle. 片語搭配

卻與年度週期毫無關係。

Day and night are caused by Earth rotating about its axis.

晝夜是由地球繞其軸線自轉引起的。

When you're on the side facing the Sun,

當你身處面向太陽的那一面時，

it's daytime,

就是白天，

and when you're on the other side,

而當你身處另一面時，

it's night.

就是黑夜。

But this rotation is no more connected to the orbital motion around the Sun 文法

但這種自轉與繞太陽的軌道運動之間的聯繫，

than a ballerina spinning on the back of a truck is connected to the truck's cruising speed.

就如同在卡車後車廂裡旋轉的芭蕾舞者與卡車的行駛速度一樣毫無關聯。

Counting the number of ballerina turns to predict how long the truck takes to drive in a circle might give you a rough idea, 片語搭配

靠數芭蕾舞者旋轉的圈數來預測卡車繞圈開一圈需要多長時間，也許能讓你有個大致概念，

but it's crazy to expect it to be precise.

但指望它精確就太瘋狂了。

Counting the days to track the orbit is pretty much the same thing, 片語搭配

數著天數來追蹤軌道週期幾乎是同一回事，

and so it shouldn't be a surprise 文法

所以這並不應該令人驚訝，

when the Earth doesn't happen to make 365 complete spins in a year.

因為地球在一年裡碰巧並沒有剛好完成365次自轉。

Irritatingly,

氣人的是，

while 365 days are too few, 文法

既然365天太少，

366 days are too many and still cause the seasons to drift out of sync,

366天又太多，仍然會導致四季不同步，

just in the opposite way.

只是以相反的方式。

The solution to all this is the leap year,

這一切的解決辦法就是閏年，

where February gets an extra day,

二月份會多出一天，

but only every four years.

但每四年才出現一次。

This works pretty well as each year the calendar is about a quarter day short, 用詞

這個辦法非常管用，因為每年日曆大約少了四分之一天，

so after four years,

所以四年後，

you add an extra day to get back in alignment. 片語搭配

你加上額外的一天就能恢復同步。

Huzzah!

好耶！

The problem has been solved.

問題解決了。

Except it hasn't. 表達脈絡

然而並沒有。

Lengthening the calendar by one day every four years is slightly too much, 文法

每四年讓日曆延長一天稍微有點多了，

and the calendar still falls behind the seasons at a rate of one day per 100 years, 講解

這樣日曆仍然會以每100年滯後一天的速度落後於四季，

which is fine for the apathetic, 文法

這對無所謂的人來說沒關係，

but not for calendar designers who want everything to line up perfectly.

但對想要一切完美對齊的日曆設計者來說卻不行。

To fix the irregularity,

為了修復這種不規則性，

every century the leap year is skipped. 文法

每個世紀會跳過一次閏年。

So 1896 and 1904 were leap years, 文化背景

所以1896年和1904年是閏年，

but 1900 wasn't.

但1900年不是。

This is better,

這好多了，

but still leaves the calendar ever so slightly too fast with an error of one day in 400 years. 文法

但還是會讓日曆稍微快那麼一點，在400年裡有一天的誤差。

So an additional clause is added to the skip the century rule

所以在跳過世紀的規則裡又增加了一條附加條款，

that if the century is divisible by 400, 文法

即如果這個世紀能被400整除，

then it will be a leap year.

那麼這一年就是閏年。

So 1900 and 2100 aren't leap years,

所以1900年和2100年不是閏年，

but 2000 is.

但2000年是。

With these three rules,

有了這三條規則，

the error is now just one day off in almost 8,000 years,

現在的誤差在將近8000年裡才只有一天，

which the current calendar declares mission accomplished, 片語搭配

現行日曆宣布任務完成，

and so calls it a day. 慣用語

然後就到此為止了。

Which is probably quite reasonable because 8,000 years ago humans were just figuring out that farming might be a good idea, 講解

這或許很合理，因為8000年前人類才剛發現種田可能是個好主意，

and 8,000 years from now,

而8000年後，

we'll hopefully be using a calendar with a better date tracking system. 文法

我們希望已經在使用一套帶有更好日期追蹤系統的日曆了。

But perhaps you're a mathematician,

但也許你是個數學家，

and a 0.0001% error is an abomination in your eyes and must be removed. 慣用語

0.0001%的誤差在你眼裡就是不可饒恕的罪惡，必須被消除。

Tough luck, 語氣意圖

算你倒楣，

says the universe,

宇宙說，

because the length of a day isn't even consistent.

因為一天的長度甚至都不是恆定的。

It randomly varies a few milliseconds on average 片語搭配

它平均會隨機波動幾毫秒，

and very slowly decreases by about 1 millisecond per 100 years, 片語搭配

並且以大約每100年1毫秒的速度非常緩慢地縮減，

which means it's literally impossible to build a perfect calendar that lasts forever. 用詞

這意味著字面意義上根本不可能建立一個永遠精準的完美日曆。

In theory, 表達脈絡

理論上，

the length of a day will expand to be as long as the current month, 文法

一天的長度將會膨脹到像現在的整整一個月那麼長，

but don't worry, 語氣意圖

不過別擔心，

in practice,

實際上，

it will take tens of billions of years, 片語搭配

這需要上百億年的時間，

and our own expanding Sun will destroy the Earth long before that happens. 文法

而我們那不斷膨脹的太陽會在此之前早就把地球毀滅了。

So, all right,

所以，好吧，

not quite sure how we got from counting the days of the months 表達脈絡

不太清楚我們怎麼從數每月的日子，

to the fiery unavoidable end of all human civilization,

說到了全人類文明無法避免的烈火般終結，

unless of course we have an adequately funded space program, 文法

除非當然，我們有資金充足的太空計畫，

hint hint, 語氣意圖

瘋狂暗示，

but there you have it. 表達脈絡

但事實就是如此。

For the next eight millennia,

在接下來的八千年裡，

leap years will keep the calendar in sync with the seasons,

閏年會讓日曆與四季保持同步，

but in a surprisingly complicated way.

只不過是以一種令人驚訝的複雜方式。

You can learn a lot more about orbits,

你可以在MinutePhysics了解到更多關於軌道、

different kinds of years,

各種不同的年、

and supermassive black holes over at MinutePhysics.

以及超大質量黑洞的知識。

As always,

像往常一樣，

Henry does a great job of explaining it all in his new video. 片語搭配

Henry在他的新影片裡完美地解釋了這一切。

Go check it out. 片語動詞

快去看看吧。