文章主講 Karen, Wesley
You’re probably familiar with leap years, but have you ever heard of a leap second? Well, get ready, because this June, there will be an extra second added to the end of the month.
Like leap years, leap seconds are added to the calendar to make up for the fact that the rotation of the Earth isn’t exactly the same from year to year. However, unlike the extra day found in every fourth February, a convention that is hundreds of years old, the leap second is a relatively new feature of the calendar. Leap seconds only started in 1972, and since then 27 leap seconds have been added to the clock. In fact, this month’s extra moment of time will only be the sixth leap second since 1998.
就像閏年，閏秒是為了彌補地球自轉每年不盡相同而被加進日曆的。然而，不像每四年便會給二月多一天這個行之數百年的慣例，閏秒是日曆上相對較新的特色。閏秒是從 1972 年才開始實施，之後共有二十七個閏秒被加入時鐘。事實上，本月的新增時刻僅是自 1998 年以來的第六個閏秒。
The insertion of leap seconds is the result of the slowing rotation of the Earth. According to NASA, our days are on average two milliseconds longer than they were in 1820. This might seem like too small of a change to be noticeable, but in those 200 years, technology has improved. With the invention of the atomic clock in the 20th century, scientists could measure time with unprecedented accuracy. In 1961, Coordinated Universal Time, using the atomic clock, became the international standard for timekeeping. Under this system of measure, a day is exactly 86,400 seconds long. However, in reality, the rotation is a fraction slower.
閏秒的加入是地球自轉漸緩的結果。根據美國國家航空暨太空總署，我們現在的一天平均比 1820 年時還要長兩毫秒。這樣的改變或許細微到看似難以察覺，但在這兩百年來，科技已有了進步。隨著二十世紀的原子鐘發明，科學家得以用前所未有的精準度測量時間。1961 年，使用原子鐘的世界協調時間成為國際計時標準。在這個度量系統之下，一天的長度正好是八萬六千四百秒。然而，實際上地球自轉稍微慢了一點點。
To adjust for this discrepancy, the International Earth Rotation and Reference Systems Service has been adding leap seconds in to balance the atomic clock and the world’s rotation. The extra time is tacked on to June 30 or December 31. As for why these additional moments are so irregular, well, that’s because tides, earthquakes, and climate change can all affect the Earth’s rotation and throw off the timing by mere milliseconds.
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