地球自转变慢 2006年将晚一秒到来

New Year's Day 2006: delayed by a second

　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.
 

你准备好了吗？2006年元旦到来之前将有一分钟变成61秒。科学家们把2006年的到来推迟了一“闰秒”。此次全世界调时距上次已有7年时间，而调时的主要原因则是地球自转速度的变化。

据美国国家标准与技术协会介绍，全世界的原子钟都将在协调世界时2005年12月31日午夜加上一个闰秒。协调世界时是通用的国际标准时间。

该协会在一个通告里解释说：“新年前夜的庆祝将多出一秒。辞旧迎新的喇叭声也将延长一秒。”

而协调世界时恰好与伦敦的冬令时相吻合。在美国东部沿海，这一秒将在2005年12月31日晚上的6时59分59秒被加上。届时，世界原子钟将会显示23:59:60，再跳到00:00:00。

增加这一闰秒是为了保证协调世界时（原子时）和地球自转时间（天文时）之间的差距控制在0.9秒以内，地球自转速度的加快或减慢受到很多因素的影响，潮汐就是其中之一。据国家标准与技术协会介绍，第一个闰秒是在1972年6月30日被加入的。

该协会说，从1999年开始到最近几年，原子时和天文时一直处于同步状态，所以不需要增加一个闰秒。

尽管也有实施负闰秒制（从协调世界时中扣除一秒）的可能，但迄今为止，只有加，没有减，这说明由于受潮汐减速的影响，地球的自转速度大体上呈减慢趋势。

国际地球自转服务组织负责决定何时加减闰秒。根据国际公约，一般在12月31日或6月30日在协调世界时中加入或减去闰秒。

与其他现代科学技术相比，在高速通讯系统中，时间的精确度显得尤为重要。

leap second ：（闰秒；由原子钟计量的，向官方的计时系统中增加或扣除的一秒时间，以补偿地球自转过程中产生的变化。）