闰年并不是每四年一次：英语精读讲义

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

一个日历年由365天组成，

a number that refuses to be divided nicely, 習語

这个数字无法被整除，

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

这就是为什么我们最后会得到30天或31天的不均匀月份，

except for February, the runt of the litter, 習語

除了二月，这个月像是发育不良的小个子，

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.

那样的话这一年就有366天。

Why does that happen?

为什么会这样呢？

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

我们究竟生活在怎样一个疯狂的宇宙里，有些年份居然比其他的要长？

To answer this,

要回答这个问题，

we need to know just what is a year.

我们需要知道究竟什么是一年。

Way oversimplifying it, 表達脈絡

极度简化地说，

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

一年就是地球绕太阳转一圈所需的时间。

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

这刚好与四季的轮回相吻合。

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

那么，画一张像这样展示地球轻快地绕着太阳转的示意图很容易，

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

但在地球上准确追踪一年却很棘手，因为宇宙不提供俯瞰图。

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

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

而记录四季变迁的显而易见的方法就是计算流逝的天数，

which gives you a 365 day calendar.

这样你就有了一个365天的日历。

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

但一旦你开始使用这个日历，

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

它就会慢慢与四季脱节，

and with each passing year, 短語搭配

随着时间流逝，

the gap gets bigger and bigger and bigger. 語法

差距会变得越来越大。

In three decades,

三十年后，

the calendar will be off by a week, 用詞

日历就会偏差一个星期，

and in a few hundred years,

而几百年后，

the seasons would be flipped,

四季就会完全颠倒，

meaning Christmas celebrations taking place in summer,

意味着圣诞庆祝活动会在夏天举行，

which would be crazy.

这简直太疯狂了。

Why does this happen?

为什么会发生这种情况？

Did we count the days wrong?

是我们算错天数了吗？

Well,

其实，

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

日历预测地球绕太阳转一圈所需的时间是8760小时，

but if you actually timed it with a stopwatch, 語法

但如果你真的用秒表去计时，

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

你会发现一年实际上比日历预测的时间长了近六个小时。

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

所以我们的日历走得比季节的实际更迭稍微快了一点点。

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

于是我们来到了所有日历的根本问题。

The day-night cycle,

昼夜交替，

while easy to count, 語法

虽然容易计算，

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

却与年度周期毫无关系。

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

昼夜是由地球绕其轴线自转引起的。

When you're on the side facing the Sun,

当你身处面向太阳的那一面时，

it's daytime,

就是白天，

and when you're on the other side,

而当你身处另一面时，

it's night.

就是黑夜。

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

但这种自转与绕太阳的轨道运动之间的联系，

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

就如同在卡车后车厢里旋转的芭蕾舞者与卡车的行驶速度一样毫无关联。

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

靠数芭蕾舞者旋转的圈数来预测卡车绕圈开一圈需要多长时间，也许能让你有个大致概念，

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

但指望它精确就太疯狂了。

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

数着天数来追踪轨道周期几乎是同一回事，

and so it shouldn't be a surprise 語法

所以这并不应该令人惊讶，

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

因为地球在一年里碰巧并没有刚好完成365次自转。

Irritatingly,

气人的是，

while 365 days are too few, 語法

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，仍然会导致四季不同步，

just in the opposite way.

只是以相反的方式。

The solution to all this is the leap year,

这一切的解决办法就是闰年，

where February gets an extra day,

二月份会多出一天，

but only every four years.

但每四年才出现一次。

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

这个办法非常管用，因为每年日历大约少了四分之一天，

so after four years,

所以四年后，

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

你加上额外的一天就能恢复同步。

Huzzah!

好耶！

The problem has been solved.

问题解决了。

Except it hasn't. 表達脈絡

然而并没有。

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

每四年让日历延长一天稍微有点多了，

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

这样日历仍然会以每100年滞后一天的速度落后于四季，

which is fine for the apathetic, 語法

这对无所谓的人来说没关系，

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

但对想要一切完美对齐的日历设计者来说却不行。

To fix the irregularity,

为了修复这种不规则性，

every century the leap year is skipped. 語法

每个世纪会跳过一次闰年。

So 1896 and 1904 were leap years, 文化背景

所以1896年和1904年是闰年，

but 1900 wasn't.

但1900年不是。

This is better,

这好多了，

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

但还是会让日历稍微快那么一点，在400年里有一天的误差。

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

所以在跳过世纪的规则里又增加了一条附加条款，

that if the century is divisible by 400, 語法

即如果这个世纪能被400整除，

then it will be a leap year.

那么这一年就是闰年。

So 1900 and 2100 aren't leap years,

所以1900年和2100年不是闰年，

but 2000 is.

但2000年是。

With these three rules,

有了这三条规则，

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

现在的误差在将近8000年里才只有一天，

which the current calendar declares mission accomplished, 短語搭配

现行日历宣布任务完成，

and so calls it a day. 習語

然后就到此为止了。

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

这或许很合理，因为8000年前人类才刚发现种田可能是个好主意，

and 8,000 years from now,

而8000年后，

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

我们希望已经在使用一套带有更好日期追踪系统的日历了。

But perhaps you're a mathematician,

但也许你是个数学家，

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

0.0001%的误差在你眼里就是不可饶恕的罪恶，必须被消除。

Tough luck, 語氣意圖

算你倒霉，

says the universe,

宇宙说，

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

因为一天的长度甚至都不是恒定的。

It randomly varies a few milliseconds on average 短語搭配

它平均会随机波动几毫秒，

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

并且以大约每100年1毫秒的速度非常缓慢地缩减，

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

这意味着字面意义上根本不可能建立一个永远精准的完美日历。

In theory, 表達脈絡

理论上，

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

一天的长度将会膨胀到像现在的整整一个月那么长，

but don't worry, 語氣意圖

不过别担心，

in practice,

实际上，

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

这需要上百亿年的时间，

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

而我们那不断膨胀的太阳会在此之前早就把地球毁灭了。

So, all right,

所以，好吧，

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

不太清楚我们怎么从数每月的日子，

to the fiery unavoidable end of all human civilization,

说到了全人类文明无法避免的烈火般终结，

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

除非当然，我们有资金充足的太空计划，

hint hint, 語氣意圖

疯狂暗示，

but there you have it. 表達脈絡

但事实就是如此。

For the next eight millennia,

在接下来的八千年里，

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

闰年会让日历与四季保持同步，

but in a surprisingly complicated way.

只不过是以一种令人惊讶的复杂方式。

You can learn a lot more about orbits,

你可以在MinutePhysics了解到更多关于轨道、

different kinds of years,

各种不同的年、

and supermassive black holes over at MinutePhysics.

以及超大质量黑洞的知识。

As always,

像往常一样，

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

Henry在他的新视频里完美地解释了这一切。

Go check it out. 短語動詞

快去看看吧。