Some of the recent postings on GMT and UTC contain inaccuracies and
half-truths. It was to set the record straight that I wrote the article on GMT
and UTC in the first place. It's enough to drive a professor to drink (feel
free to send some 18 yr. Macallan single malt!). For those who haven't yet
had a chance to read my article:
1) UTC is not a French acronym. They used to use TUC as an acronym but they
now use UTC along with everyone else. Before UTC, we had UT0, UT1, and UT2.
So it was obvious that Coordinated Universal Time should be UTC and not CUT.
2) When the Gregorian calendar was introduced in 1582, 10 days were dropped.
For a good on-line reference to calendar issues see Claus Tonderings's
"Frequently Asked Questions about Calendars":
<http://www.pip.dknet.dk/~pip10160/cal/calendar20.html>.
3) UT1 does not vary due to polar motion but only due to changes in the
earth's spin. The effect of polar motion is, however, in UT0.
4) GMT, if U.K. standard time is meant (which is the usual case when the term
GMT is used these days), is EXACTLY the same as, and therefore equally as
accurate as, UTC. (Different timing labs around the world maintain different
versions of UTC and through clock comparisons, chiefly using GPS, a definitive
UTC is maintained by the Bureau International des Poids et Mesures).
5) Perhaps the use of GMT as a synonym for UT1 should be deprecated.
6) UTC is actually adjusted for leap seconds, not TAI. A plot of UTC vs. TAI
over the years shows the leap second jumps.
-- Richard Langley
Professor of Geodesy and Precision Navigation
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Richard B. Langley E-mail: [EMAIL PROTECTED]
Geodetic Research Laboratory Web: http://www.unb.ca/GGE/
Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142
University of New Brunswick Fax: +1 506 453-4943
Fredericton, N.B., Canada E3B 5A3
Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/
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