Re: Time to UTC
Re: Time to UTC
- Subject: Re: Time to UTC
- From: Yvan KOENIG <email@hidden>
- Date: Thu, 7 Jan 2010 20:31:11 +0100
Le 7 janv. 2010 à 18:49, Mark J. Reed a écrit :
Whups, sent reply only to Doug.
On Thu, Jan 7, 2010 at 12:20 PM, Doug McNutt
<email@hidden> wrote:
UTC (Universal time coordinated) is atomic time based on
electronic transitions in atoms.
...as corrected by leap seconds. Uncorrected atomic time is TAI.
GMT is astronomical time based on rotation speed of Earth.
These days, what you call "GMT" above is actually called by
astronomers and physicists UT0, UT1, or UT2, depending on how much
correction is done on the raw measurements. In scientific circles,
"GMT" is no longer meaningful outside of historical references. The
label has been deprecated since 1972 - in no small part because of the
ambiguity in using it: prior to 1925, 0000 GMT was noon and 1200 GMT
was midnight, a fact which has to be taken into account when
interpreting historical observations. The UTC label has no such
ambiguity.
But that's in scientific use. More generally, the term GMT is still
in legal use in many places, including, I believe, the official
definition of the US time zones, and as the designation of UK time
when Summer Time is not in effect.
The official name for the time zone is UTC, so the function names
should probably be changed, or at least an alias provided. But it
should be noted that most computers don't actually use UTC, because
they don't take leap seconds into account when manipulating historical
dates. Instead, they effectively move the zero point forward in time
by one second every time a leap second is introduced.
If you set the computer clock using the internet once a day you're
surely using atomic time corrected for any previously known leap
seconds. That would be
GMT.
No, that would be UTC. Uncorrected atomic time is TAI.
If ISO 8610 wished to keep the formula 'time to GMT' it would have
done. Great Britain tried to keep it but it was rejected.
http://fr.wikipedia.org/wiki/Temps_universel_coordonné
This one states:
UTC et GMT
L’utilisation de l’ancienne appellation standard temps moyen de
Greenwich (GMT, de l’anglais Greenwich Mean Time) est désormais
déconseillée parce que sa définition est ambiguë, au contraire
d’UTC, qui doit lui être préféré.
Ce sigle s’était imposé par la prépondérance de la marine
britannique durant le XIXe siècle et fut plus tard rebaptisé Temps
universel (UT, de l’anglais Universal time).
Comme le temps UTC est le temps civil du méridien origine des
longitudes à Greenwich, la Grande-Bretagne tente bien de prolonger
l’usage de GMT en le traduisant désormais par Greenwich Meridian
Time ; mais cette expression n’a aucune valeur officielle.
http://en.wikipedia.org/wiki/Coordinated_Universal_Time#cite_ref-11
This other one states:
For most common and legal-trade purposes, the fractional second
difference between UTC and UT (GMT) is inconsequentially small, so
UTC is often called GMT, for example by the BBC, although that usage
is ambiguous.[23]
UTC has been adopted as legal time in the Title 15 of the US Code,
section 261b.
So, I feel that it would be logical that when we type 'Time to GMT'
in the script editor, it will be automatically replaced by 'Time to
UTC'.
I really don't understand why Apple remains sticked to deprecated
terminology.
GMT is an example but there is an other one: the currencies
abbreviations.
Yvan KOENIG (VALLAURIS, France) jeudi 7 janvier 2010 20:31:06
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