# 一秒鐘的問題......

一秒鍾 是怎樣定出來的??

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The second (abbreviation, s or sec) is the Standard International (SI) unit of time. One second is the time that elapses during 9,192,631,770 (9.192631770 x 109) cycles of the radiation produced by the transition between two levels of the cesium 133 atom.

There are other expressions for the second. It is the time required for an electromagnetic field to propagate 299,792,458 meters (2.99792458 x 108 m) through a vacuum. This figure is sometimes rounded to 3.00 x 108 m, or 300,000 kilometers (3.00 x 105 km). One second is equal to 1/86,400 of a mean solar day. This is easy to derive from the fact that there are 60 seconds in a minute, 60 minutes in an hour, and 24 hours in a mean solar day. This definition is, however, subject to limited accuracy because of irregularities in the earth's orbit around the sun.

Engineers and scientists often use smaller units than the second by attaching power-of-10 prefix multipliers. One millisecond is 10-3 s; one microsecond is 10-6 s; one nanosecond is 10-9 s; one picosecond is 10-12 s. During these spans of time, respectively, an EM field propagates through a vacuum over distances of approximately 300 kilometers, 300 meters, 300 millimeters, and 300 micrometers.

The second is sometimes specified as a unit of angular measure, especially in astronomy and global positioning. In these contexts, it is also known as an arc second or a second of arc, and is equal to exactly 1/3600 of an angular degree or 1/1,296,000 of a circle. Sixty arc seconds comprise an arc minute; 60 arc minutes comprise an angular degree. One arc second of latitude at the earth's surface corresponds to a north-south distance of only about 31 m.

Also see Standard International (SI) System of Units and prefix multipliers.

好棒阿...拍拍手，我了解了

翻譯的不好勿見怪~~

秒鐘(簡稱、s 或秒) 是標準國際(SI) 時間單位。一秒是流逝在輻射期間的9,192,631,770 個的時間(9.192631770 x 109) 週期由轉折引起在銫133 原子之間的二個水平。有其它表示為秒鐘。這是需時為一個電磁場繁殖299,792,458 米(2.99792458 x 108 m) 通過真空。這個圖有時被環繞對3.00 x 108 m, 或300,000 公里(3.00 x 105 公里) 。一秒是相等的到一卑鄙太陽天的1/86,400 。

2004-12-16 15:59:18 補充：

這容易從事實有60 秒在一分鐘內, 60 分鐘在一個小時內, 和24 小時獲得在一卑鄙太陽天。這個定義是, 然而, 依於有限的準確性由於不規則性在地球的軌道在太陽附近。工程師和科學家由附有經常使用更小的單位比秒鐘力量10 前綴乘算器。

2004-12-16 15:59:31 補充：

一毫秒是10-3 s; 一微秒是10-6 s; 一納秒是10-9 s; 一微微秒是10-12 s 。在時間期間這些間距, 各自, EM 領域繁殖通過真空在距離大約300 公里、300 米、300 毫米, 和300 個測微表。秒鐘有時被指定作為有角措施單位, 特別是在天文和全球性安置。在這些上下文, 這其次是亦稱弧或一秒鐘弧, 和是相等的到有角程度的確切地圈子的1/3600 或1/1,296,000 。六十弧秒鐘包括一弧分鐘; 60 弧分鐘包括有角程度。一弧緯度在地球的表面其次對應於一個南北距離僅僅大約31 m 。也參見標準國際(SI) 單位制度和前綴乘算器。