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发表于 2012-10-3 18:27:33
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What time is it? One of the commonest questions uttered
around the World but what exactly are we asking? You ask someone in China what
the time is then you will certainly get a different answer if you ask an
American,i文明用户el marant pas cher, obviously their time-zones are on the opposite side of the world.
But what if you ask two people in the same room as you? You
may get the same answer from them both but then again one persons watch may be
a minute or two faster.
When we ask the time then what we are really asking for is a
rough estimate for the time zone that we are in. Some watches are more accurate
than other文明用户ut it is often enough for our day to day needs.
But what if you need to know the exact time and what if you
need to know what that time is another country too. Perhaps you have bought an
airline ticket; it would be disappointing to turn up at the airport only to be
told that your ticket was sold to somebody else in as the clock at their travel
agent was slower than the one where you bought your ticket.
So how does global industry keep accurate time with one
another? The answer is quite simple and it is called Coordinated Universal Time
or UTC.
The International Bureau of Weights and Measures acts
as the official time-keeper for the globe and started UTC in 1972 after the
development of atomic clocks.
The atomic clock was first developed in the late 50s when
it was discovered the atom caesium-133 resonates at an exact frequency of 9,coach handbags online,192,cheap nfl jerseys free shipping,631,770
every second. This frequency was so exact that atomic clocks developed an
accuracy of one second in 1.4million years and The International System of
Units defined the second as the frequency of the caesium-133 atom and an
international unit for measuring time wa文明用户orn.
However, atomic clocks are even more accurate than the Earth
itself which is actually slowing in its rotation. This slowing is only small
but if the standard system of time, UTC,cheap jerseys,elite jerseys, didnt compensate for it, eventually
midnight would fall in the middle of the day so leap seconds are added every few years to compensate.
The only problem with UTC timepieces is that atomic clocks are
enormous in both size and cost. In fact they are generally only to be found in
large scale physics laboratories such as NPL or
through specialist GPS or radio time servers. These time servers make use of
NTP which ha文明用户een developed over the last 25 years to
keep computer networks synchronized so they do not have to rely on their
inaccurate internal clocks.
NTP servers and UTC have allowed industry to become truly
global and made pos文明用户le technologies such as communication satellites, mobile
phones,cheap nfl jerseys, sat-nav and ATMs that we all take for granted.
Article Tags:
Atomic Clocks
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