That's right, a year is not 365 days.

沒錯，一年不是 365 天。

It's 365.24219 days, which means our 365-day calendar is off by a quarter of a day, or about six hours every year.

是 365.24219 天，也就是說我們的 365 天日曆偏離了四分之一天，每年偏離了六個小時左右。

It's pretty annoying.

這相當煩人。

Julius Caesar thought so too.

凱撒大帝也這麼認為。

Back in 45 BC, he came up with a solution.

早在公元前 45 年，他就想出了一個辦法。

For three years, we ignore that extra quarter of a day, then every four years, we add those four quarter days back together and stick an extra day at the end of February.

三年的時間，我們忽略多出的那四分之一天，然後每四年，我們把這四分之一天加在一起，在二月底多加一天。

Without that leap day, the gap between the calendar year and the true year would gradually increase.   

如果沒有閏日，公曆年和真正的年份之間的差距會逐漸加大。

After 100 years, the calendar would be off about about 25 days.

100 年後，日曆會偏差約 25 天左右。

So, why does this matter?

那麼，為什麼會有這個問題呢？

Billions of years ago, something smashed into Earth and knocked its axis about 23 degrees.

幾十億年前，有個東西砸向地球，把地球軸心撞偏了 23 度。

And thus, were born the seasons.

於是，四季誕生了。

Winter when we're tilted away from the sun, and summer when we're tilted toward it.

冬天，我們遠離太陽；夏天，我們傾向太陽。

And we're used to these seasons lining up with our calendar.

而我們已經習慣了相應季節與日曆配合。

It's handy for all sorts of record-keeping.

這便於各種記錄保存。

But without leap year, our calendar would become disconnected from the seasons.

但如果沒有閏年，日曆就會與季節脫節。

After 700 years or so, Christmas would show up in the middle of summer.

700 多年後，聖誕節會出現在夏天的中間。

We'd have Thanksgiving in the spring, St. Patrick's Day in the fall, and Labor Day in the winter.

我們會在春天過感恩節、秋天過聖派翠克節、冬天過勞動節。

Chaos!

大混亂！

It's still not a perfect system though.

不過這仍然不是完美的系統。

Leap year actually overcorrects slightly, so every 100 years we skip a leap day.

閏年其實會稍微矯枉過正，所以每隔 100 年我們會跳過一個閏日。

But that puts the calendar slightly behind again, so we skip skipping leap day every 400 years.

但這樣一來，曆法又會稍微落後了一些，所以每 400 年又會跳過一次閏日。

And even still, after a few thousand years, we'll be off again by a day.

即便如此，幾千年後，我們還是會偏差一天。