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From: devine@vianet.UUCP (Bob Devine)
Newsgroups: sci.astro
Subject: Re: Coordinated Universal Time
Message-ID: <49@vianet.UUCP>
Date: Fri, 31-Oct-86 18:30:06 EST
Article-I.D.: vianet.49
Posted: Fri Oct 31 18:30:06 1986
Date-Received: Mon, 3-Nov-86 22:54:02 EST
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  Sorry for coming in late on this, I just got around to reading this
group (usenet 250 groups and climbing...).

  Here are the real definitions of UTC, UT1, etc

  UTC is the "Coordinated Universal Time".  The "coordinated" part comes
from an agreement of the signatory countries to the International Time
Bureau (which is shorted to BIH, natch) based in Paris.  There are about
150 atomic clocks used across the world.

  UT1 (<-- that's a one) can be thought of as a clock based on the rotating
Earth.  Because the Earth's rotation is less accurate -- it wobbles and
speeds up or slows down -- the UT1 and UTC clocks are not always in
agreement.  UTC is changed to be within 1.0 second of UT1 by the insertion
or deletion of "leap seconds".

  Zulu is used by the military/communiction folks to refer to the timezone
based upon the 0 degree longitude line that goes through the Greenwich
Observatory.  All of the 24 timezones have letter names.

  GMT was the time maintained by the Greenwich Observatory clocks.  It came
to be used as the basis for timezone- and daylight saving time-independent
clock readings.  Last year, the Observatory decided to not replace its clocks
when they break because of monetary reasons; they had a fixed budget and are
going to use the saved money for astronomic purposes.

  In 1884, the Observatory was chosen as the 0 degree point over the city of
Paris, making lots of French folks mad.  But remember, they got even by having
the BIH headquartered in Paris and the term initials are put backwards (just
teasing, so don't through baguettes :-).

Bob Devine