地球自轉變慢 2006年將晚一秒到來

地球自轉變慢 2006年將晚一秒到來


Scientists are delaying the start of 2006 by a leap second.
Get ready for a minute with 61 seconds. Scientists are delaying the start of 2006 by the first "leap second" in seven years, a timing tweak meant to make up for changes in the Earth's rotation.

The adjustment will be carried out by sticking an extra second into atomic clocks worldwide at the stroke of midnight Coordinated Universal Time, the widely adopted international standard, the U.S. National Institute of Standards and Technology said. "Enjoy New Year's Eve a second longer," the institute said in an explanatory notice. "You can toot your horn an extra second this year." Coordinated Universal Time coincides with winter time in London.

On the U.S. East Coast, the extra second occurs just before 7 p.m. on New Year's Eve. Atomic clocks at that moment will read 23:59:60 before rolling over to all zeros. A leap second is added to keep uniform timekeeping within 0.9 second of the Earth's rotational time, which can speed up or slow down because of many factors, including ocean tides.

The first leap second was added on June 30, 1972, according to NIST. Since 1999 until recently, the two time standards have been in close enough synch to escape any need to add a leap second, NIST said.

Although it is possible to have a negative leap second -- that is, a second deducted from Coordinated Universal Time -- so far all have been add-ons, reflecting the Earth's general slowing trend due to tidal braking. Deciding when to introduce a leap second is the responsibility of the International Earth Rotation and Reference Systems Service.


Under an international pact, the preference for leap seconds is December 31 or June 30. Precise time measurements are needed for high-speed communications systems among other modern technologies.  

(Agencies)         你準備好了嗎？2006年元旦到來之前將有一分鐘變成61秒。科學家們把2006年的到來推遲了一「閏秒」。此次全世界調時距上次已有7年時間，而調時的主要原因則是地球自轉速度的變化。 據美國國家標準與技術協會介紹，全世界的原子鐘都將在協調世界時2005年12月31日午夜加上一個閏秒。協調世界時是通用的國際標準時間。

該協會在一個通告里解釋說：「新年前夜的慶祝將多出一秒。辭舊迎新的喇叭聲也將延長一秒。」 而協調世界時恰好與倫敦的冬令時相吻合。在美國東部沿海，這一秒將在2005年12月31日晚上的6時59分59秒被加上。屆時，世界原子鐘將會顯示23:59:60，再跳到00:00:00。 增加這一閏秒是為了保證協調世界時（原子時）和地球自轉時間（天文時）之間的差距控制在0.9秒以內，地球自轉速度的加快或減慢受到很多因素的影響，潮汐就是其中之一。

據國家標準與技術協會介紹，第一個閏秒是在1972年6月30日被加入的。 該協會說，從1999年開始到最近幾年，原子時和天文時一直處於同步狀態，所以不需要增加一個閏秒。 儘管也有實施負閏秒制（從協調世界時中扣除一秒）的可能，但迄今為止，只有加，沒有減，這說明由於受潮汐減速的影響，地球的自轉速度大體上呈減慢趨勢。


國際地球自轉服務組織負責決定何時加減閏秒。根據國際公約，一般在12月31日或6月30日在協調世界時中加入或減去閏秒。 與其他現代科學技術相比，在高速通訊系統中，時間的精確度顯得尤為重要。

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