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• To understand leap year, you have to know this one fact: Earth rotates 365.24219 times during one full orbit of the sun.

要了解閏年，你必須知道這個事實：繞完整太陽軌道一圈，地球會自轉 365.24219 次。

• 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。

To understand leap year, you have to know this one fact: Earth rotates 365.24219 times during one full orbit of the sun.

# 為什麼四年才有一次 2/29？原來閏年的緣由是這樣！(How leap year works)

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Shinichiro 發佈於 2022 年 05 月 05 日