Vietnam timezone history probably wrong
alois at astro.ch
Wed May 18 14:07:08 UTC 2011
tzdata gives for Vietnam timezone
# From Shanks & Pottenger:
# Zone NAME GMTOFF RULES FORMAT [UNTIL]
Zone Asia/Ho_Chi_Minh 7:06:40 - LMT 1906 Jun 9
7:06:20 - SMT 1911 Mar 11 0:01 #
7:00 - ICT 1912 May
8:00 - ICT 1931 May
7:00 - ICT
This is possibly wrong for the years beween 1911 and 1976.
I am us9ing the source
Gabriel, Traite de l'heure dans le monde, edition 1991.
It deals with Vietnam under the entry 'Indochine Française' until 1954,
and then separately with North and South Vietnam, until the unification
Gabriel gives this timezone information:
French Indochina (including Vietnam, Cambodia, Laos)
until 1 July 1906: local mean time
until 1 May 1911: 7h6m44s east (meridian of Saigon)
until 1 Jan 1943: 7h east
from 1 Jan 1943: 8h east
(with Daylight saving time, i.e. 9h east, between 14 March and 1 Sept 1945)
until 15 April 1955: 8h east
until 1 Jan 1960: 7h east
until 1976 : 8h east
For 1976, Gabriel does not give a transition date. The official
reunification was on 2 July 1976.
since 1976: 7h east
until 1976 (for date, see above): 8h east
since 1976: 7h east
I have searched for corroboration of the fact that Vietnam was on GMT +
8h in years when tzdata and Shanks claim 7h.
For siginificant timed events during the Vietnam war, there must be
newspaper reports which give local Vietnam time and corresponding US time.
One such report I have found is the last helicopter out of Saigon,
according to TIME magazine.
Finally, at 5 p.m. Washington tune—it was then 5 a.m. in
Saigon—Kissinger told the President that Martin was closing down the
embassy and destroying its communications equipment. Minutes later, a
helicopter broadcast the message: "Lady Ace Zero Nine, Code Two is
aboard." Lady Ace 09 was the chopper's own call signal; Code Two
designates an ambassador.
This is 5 PM on 29 Paril 1975. Washington DC was on DST, i.e. on 4h west
timezone. Universal time is 21:00 (09 pm).
In Vietnam it is already the 30th of April, 5 am, in the morning. This
means that Vietnam was 8 hours ahead of Universal time!
This means that, at least for April 1975, the source Gabriel is right
and Shanks and tzdata are wrong, because they claim 7h east.
Conclusion: it is evident that Vietnam timezone history needs
corrections, also in tzdata, because it should be correct at least
starting from 1970.
I would be reluctant to simply copy the Gabriel source, as it fails to
give a transition date in 1976. But research is needed. The best would
be local Newspaper archives in Saigon or Hanoi, if such exist.
|| Alois Treindl, Astrodienst AG, mailto:alois at astro.com
|| Zollikon/Zurich, Switzerland
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