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.
你或許對閏年耳熟能詳，但你有聽過閏秒嗎？那準備好囉，因為今年六月底會多一秒。
a leap year閏年 a leap second閏秒
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.
make up for... = compensate for... 彌補…… rotation [ roˈteʃən ] n.（星球）自轉，旋轉
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.
atomic [ əˈtɑmɪk ] a. 原子的 unprecedented [ ʌnˈprɛsəˌdɛntɪd ] a. 前所未有的 timekeeping [ ˈtaɪmˌkipɪŋ ] n. 計時
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.
