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2004年09月24日
Time
The mother clock. This is where Canadians go if they really want the time:
The Frequency and Time Group at the Institue of National Measurement Standards of the National Research Council of Canada is responsible for "official time". Canada's caesium atomic clocks, like the one above, are used in conjunction with atomic clocks from around the world to maintain an internationally accepted time scale known as UTC, Co-ordinated Universal Time.
Greenwich Mean Time (GMT) is a scale based on the position of the sun with reference to the old Greenwich observatory in England at zero degrees longitude. As astronomers and scientists discovered and began to account for discrepancies in timekeeping caused by the inconsistency of the Earth's rotation, new standards were created to replace GMT.
The current standard, UTC, is based on counting seconds. A second was defined in 1967 by the International System of Units (SI) as 9,192,631,770 cycles of radiation in the caesium-133 atom. A day is 86,400 seconds based on the rotation of the earth in the reference year 1900. Because our clocks are now more precise than the Earth's rotation, leap seconds are added every once in a while to keep time in sync with the Earth. Upcoming leap seconds are predicted by the International Earth Rotation Service (IERS).
The acronym UTC is derived from a compromise between the French "Temps Universel Coordonné" (TUC) and the English "Co-ordinated Universal Time" CUT.
References:
http://en.wikipedia.org/wiki/Atomic_clock
http://inms-ienm.nrc-cnrc.gc.ca/time_services.html
http://www.apparent-wind.com/gmt-explained.html
UPDATE:
I forgot to include, of course, the Canadian NTP time server: time.nrc.ca
Use this server to automatically synchronize your computer clock using WinXP, Linux, or a number of free utilities available for download.
Posted by William at 2004年09月24日 01:54