fisher@star.dec.com (Burns Fisher ZKO1-1/D42 DTN 381-1466) (10/14/86)
>> Universal time is actually just another name for Greenwich mean time. > >It's worse than that. A while back I called WWV here in town, and was >told that (as far as the fellow I talked with knew), the proper name, as >is used by WWV, is "coordinated universal time". This should be >abbreviated CUT, but I've seen it as UCT instead. > UCT are the initials in French. It was my understanding that UT was actually slightly different from GMT in that UT explicitly includes all the corrections (leap second, etc) that are broadcast on WWV, while GMT is not defined so precisely. (Note that I don't mean to imply that WWV defines UT...I always imagined that it was defined by the same folks who are the keepers of the standard meter in Paris.) Burns
ajs@hpfcla.HP.COM (Alan Silverstein) (10/16/86)
> The proper abbreviation is UCT...
No, UTC. I goofed. So stop listening to me. :-)chuckb@fluke.UUCP (Chuck Bowden) (10/16/86)
> >> Universal time is actually just another name for Greenwich mean time. > > > >It's worse than that. A while back I called WWV here in town, and was > >told that (as far as the fellow I talked with knew), the proper name, as > >is used by WWV, is "coordinated universal time". This should be > >abbreviated CUT, but I've seen it as UCT instead. > > > UCT are the initials in French. > > It was my understanding that UT was actually slightly different from GMT > in that UT explicitly includes all the corrections (leap second, etc) that are > broadcast on WWV, while GMT is not defined so precisely. (Note that I don't > mean to imply that WWV defines UT...I always imagined that it was defined > by the same folks who are the keepers of the standard meter in Paris.) > > Burns One small point: The initials for Coordinated Universal Time are UTC, not UCT. The part about the initials being in French is correct, but the order is UTC. (You see "UTC" used all the time on shortwave radio contact QSL cards from all over the world; probably because French is considered the international language of diplomacy.) Chuck Bowden, KD7LZ
devine@vianet.UUCP (Bob Devine) (11/01/86)
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
phil@brl-smoke.ARPA (Phil Dykstra <phil>) (11/09/86)
[Another late addition...]
Universal Time: the basis of civil timekeeping; based on
observations of diurnal motion. Several flavors:
U.T.0: determined directly by observation.
U.T.1: U.T.0 corrected for variations in the meridian of the
observer due to observed motion of the geographic poles.
U.T.2: U.T.1 corrected for mean seasonal variations in the
earth's ratation rate.
U.T.C: A stepped atomic system of time which is kept close to
U.T.1 by the introduction of discontinuities.
In theory U.T.0 -> U.T.2 are continuously variable and can
only be determined precisely after the fact (particularly U.T.2
which requires several months of observation). This is
inconvenient to say the least so U.T.C runs at a constant
rate and inserts step discontinuities to keep in sync.
The rules are (with a couple of exceptions of course):
Prior to 1972: 0.1 second jumps when 0.1 second discrepancies occur.
Post 1972: 1.0 second jumps at 0.7 second discrepancies. These
jumps now only occur at 0h U.T. on the first day of a month.
The difference between U.T.C and U.T.1 is claimed to be sent
in encoded form by most of the time standard stations.
For a splendidly complex albeit very precise discussion of
time systems, see the explainatory section of "The American
Ephemeris and Nautical Almanac."
- Phil