UTC vs GMT

Fri Oct 4 02:24:47 UTC 1996

In message <199610032320.QAA04986 at shade.twinsun.com>, Paul Eggert wrote:

> That's a good suggestion for Etc/UTC and Etc/Universal, since anybody
> who chooses those zones probably wants `UTC'.  (Also, Etc/UCT should
> probably generate `UCT' instead of the current `GMT'.)

What is UCT supposed to mean and why is it defined there? I have never
heard this term before. Is it supposed to be "Universal Coordinated
Time"???

Two alternative original abbreviation proposals were CUT (English:
Coordinated Universal Time) and TUC (francais: temps universel
coordine), but UTC was selected both as a compromise between the
French and English proposals and because the C at the end looks more
like an index in UT0, UT1, UT2 and a mathematical style notation is
always the most international approach.

See also <URL:http://www.boulder.nist.gov/timefreq/faq/faq.htm>:

  Why is the abbreviation for Coordinated Universal Time "UTC" instead
  of "CUT"?

  In 1970 the Coordinated Universal Time system was devised by an
  international advisory group of technical experts within the
  International Telecommunication Union (ITU). The ITU felt it was best
  to designate a single abbreviation for use in all languages in order
  to minimize confusion.  Since unanimous agreement could not be
  achieved on using either the English word order, CUT, or the French
  word order, TUC, a compromise of using neither, UTC, was adopted.

  Is Coordinated Universal Time (UTC) the same thing as Greenwich Mean
  Time (GMT)?

  Greenwich Mean Time (GMT) is a 24 hour astronomical time system based
  on the local time at Greenwich, England. GMT can be considered
  equivalent to Coordinated Universal Time (UTC) when fractions of a
  second are not important. However, by international agreement, the
  term UTC is recommended for all general timekeeping applications, and
  use of the term GMT is discouraged.

> As far as I know, GMT hasn't been an official reference time since the 1920s.

Yes, I have seen various references to some IAU conference in 1928
where an agreement was reached that the term Univeral Time (UT) shall
be used, and this term has since then indeed be used quite
consistently in the astronomical literature.  I have never read GMT in
any recent paper in "Astronomy and Astrophysics", only UT (especially
when second precision is not relevant), or UTC/UT1/etc. if subsecond
precision is relevant.

>From <URL:http://community.bellcore.com/mbr/gmt-explained.html>:

  In 1928, the International Astronomical Union recommended that the   
  time used in the compilation of astronomical almanacs, essentially   
  GMT, or what was also sometimes called Greenwich Civil Time, be   
  referred to as Universal Time.  The terms "Universal Time" and   
  "Universal Day" were introduced at the various conferences in the   
  1800's held to set up the standard time system.

> Even though the reference standard has changed a few times since then,
> the public continues to call it `GMT'.

I feel, GMT is only widely known in English speaking countries. In
Germany for instance, the term Weltzeit (translates as "world time" or
may be "universal time") is usualy used (for example on shortwave
radio, Deutsche Welle ~6.1 MHz) and the time zone map that you'll find
in geography school books and for example in the information booklets
in every Lufthansa plane say UTC and not GMT.

BTW: Quite a number of on-line ressources about time are available on
<URL:http://www.yahoo.com/Science/Weights_and_Measures/Measurements/Time/>.

I would exchange GMT for UTC as in the patch below.  This patch also
removes UCT, assuming that this is the abbreviation for "Universal
Coordinated Time", something I have never encountered outside the
etcetera file.

Markus

-- 
Markus G. Kuhn, Computer Science grad student, Purdue
University, Indiana, USA -- email: kuhn at cs.purdue.edu

--- etcetera.orig	Thu Oct  3 20:08:28 1996
+++ etcetera	Thu Oct  3 21:13:49 1996
@@ -1,55 +1,60 @@
 # @(#)etcetera	7.5
 
 # All of these are set up just so people can "zic -l" to a timezone
 # that's right for their area, even if it doesn't have a name or DST rules
 # (half hour zones are too much to bother with -- when someone asks!)
 
+Zone	Etc/UTC		0	-	UTC
+Link	Etc/UTC				Etc/Universal
+Link	Etc/UTC				Etc/UTC-0
+Link	Etc/UTC				Etc/UTC+0
+Link	Etc/UTC				Etc/UTC0
+Link	Etc/UTC				Etc/Zulu
+
+# Since the early 1970s, UTC has been the correct official term for
+# the international reference time zone defined in ITU-R
+# Recommendation TF.460-4.  For old-fashioned British patriots, we
+# still offer the classic name of this time zone:
+
 Zone	Etc/GMT		0	-	GMT
-Link	Etc/GMT				Etc/UTC
-Link	Etc/GMT				Etc/UCT
-Link	Etc/GMT				Etc/Universal
 Link	Etc/GMT				Etc/Greenwich
-Link	Etc/GMT				Etc/Zulu
-Link	Etc/GMT				Etc/GMT-0
-Link	Etc/GMT				Etc/GMT+0
-Link	Etc/GMT				Etc/GMT0
 
 # We use POSIX-style signedness in the names and output,
 # internal-style signedness in the specifications.
-# For example, TZ=Etc/GMT+4 corresponds to 4 hours _behind_ GMT;
-# it is equivalent to TZ=GMT+4, which is implemented directly as per POSIX.
+# For example, TZ=Etc/UTC+4 corresponds to 4 hours _behind_ UTC;
+# it is equivalent to TZ=UTC+4, which is implemented directly as per POSIX.
 
 # Earlier incarnations of this package were not POSIX-compliant,
 # and had lines such as
-#		Zone	GMT-12		-12	-	GMT-1200
+#		Zone	UTC-12		-12	-	UTC-1200
 # We did not want things to change quietly if someone accustomed to the old
 # way does a
-#		zic -l GMT-12
+#		zic -l UTC-12
 # so we moved the names into the Etc subdirectory.
 
-Zone	Etc/GMT-14	14	-	GMT-14	# 14 hours ahead of GMT
-Zone	Etc/GMT-13	13	-	GMT-13
-Zone	Etc/GMT-12	12	-	GMT-12
-Zone	Etc/GMT-11	11	-	GMT-11
-Zone	Etc/GMT-10	10	-	GMT-10
-Zone	Etc/GMT-9	9	-	GMT-9
-Zone	Etc/GMT-8	8	-	GMT-8
-Zone	Etc/GMT-7	7	-	GMT-7
-Zone	Etc/GMT-6	6	-	GMT-6
-Zone	Etc/GMT-5	5	-	GMT-5
-Zone	Etc/GMT-4	4	-	GMT-4
-Zone	Etc/GMT-3	3	-	GMT-3
-Zone	Etc/GMT-2	2	-	GMT-2
-Zone	Etc/GMT-1	1	-	GMT-1
-Zone	Etc/GMT+1	-1	-	GMT+1
-Zone	Etc/GMT+2	-2	-	GMT+2
-Zone	Etc/GMT+3	-3	-	GMT+3
-Zone	Etc/GMT+4	-4	-	GMT+4
-Zone	Etc/GMT+5	-5	-	GMT+5
-Zone	Etc/GMT+6	-6	-	GMT+6
-Zone	Etc/GMT+7	-7	-	GMT+7
-Zone	Etc/GMT+8	-8	-	GMT+8
-Zone	Etc/GMT+9	-9	-	GMT+9
-Zone	Etc/GMT+10	-10	-	GMT+10
-Zone	Etc/GMT+11	-11	-	GMT+11
-Zone	Etc/GMT+12	-12	-	GMT+12
+Zone	Etc/UTC-14	14	-	UTC-14	# 14 hours ahead of UTC
+Zone	Etc/UTC-13	13	-	UTC-13
+Zone	Etc/UTC-12	12	-	UTC-12
+Zone	Etc/UTC-11	11	-	UTC-11
+Zone	Etc/UTC-10	10	-	UTC-10
+Zone	Etc/UTC-9	9	-	UTC-9
+Zone	Etc/UTC-8	8	-	UTC-8
+Zone	Etc/UTC-7	7	-	UTC-7
+Zone	Etc/UTC-6	6	-	UTC-6
+Zone	Etc/UTC-5	5	-	UTC-5
+Zone	Etc/UTC-4	4	-	UTC-4
+Zone	Etc/UTC-3	3	-	UTC-3
+Zone	Etc/UTC-2	2	-	UTC-2
+Zone	Etc/UTC-1	1	-	UTC-1
+Zone	Etc/UTC+1	-1	-	UTC+1
+Zone	Etc/UTC+2	-2	-	UTC+2
+Zone	Etc/UTC+3	-3	-	UTC+3
+Zone	Etc/UTC+4	-4	-	UTC+4
+Zone	Etc/UTC+5	-5	-	UTC+5
+Zone	Etc/UTC+6	-6	-	UTC+6
+Zone	Etc/UTC+7	-7	-	UTC+7
+Zone	Etc/UTC+8	-8	-	UTC+8
+Zone	Etc/UTC+9	-9	-	UTC+9
+Zone	Etc/UTC+10	-10	-	UTC+10
+Zone	Etc/UTC+11	-11	-	UTC+11
+Zone	Etc/UTC+12	-12	-	UTC+12

