秒[Second] - 达人(其实～我是卧底，来自外星)

2005/02/13 | 秒[Second]
类别(¤〖天文〗) | 评论(0) | 阅读(19) | 发表于 11:57: A unit of time equal to 1/60 of a minute or 1/3600 of an hour.The international definition was originally 1/86400th of a mean solar day in 1900, but is now instead the time required for 9,192,631,770 vibrations of a Cs atom. Since the speed of light is defined to be 299,792,458 m s-1, this makes the meter a derived unit. A mnemonic for the number of seconds in a year is 1 nanocentury is approximately equal to seconds (1 y = s, whereas this approximation gives s).; 0