[tz] Timezone history for some Pacific Islands.

Paul Eggert eggert at cs.ucla.edu
Mon Nov 19 07:23:38 UTC 2018

Thanks for all that work on Pacific island time zone history. Proposed patch 
attached and installed in the development version; comments welcome. Some 
comments on your remarks:

> * Then Pacific theater of WWII started and Japan slowly lose control on the
> island. The webpage I linked above contain no information during this
> period of time.

It was chaotic. The attached patch tries to fill in some of the blanks.

 > * Also, the NYT article linked in that website say the jump from GMT-12 to
 > GMT+12 in year 1993 skipped Saturday that day, however the comment in tz
 > database from that year say it skipped Friday. That seems to be an
 > inconsistency that should be investigated, and the comment should probably
 > be annotated accordingly if the comment was not accurate

Thanks, that is indeed an error in tzdata. I copied a datum from Shanks 
incorrectly: Shanks said "24:00" but I treated it as 00:00. Fixed in the 
attached patch.

> * The site also pointed out that currently tzdata say Pacific/Kwajalein
> switched from GMT+11 to GMT-12 in 1969 October without explanation, however
> an 1993 article from NYT say it synchorized its day with US mainland about
> 40 years ago and thus the switch should occur at around 1950s instead.

The NYT (actually, AP) article is vague and possibly wrong about this. The 
article says the earlier switch was "40 years ago when the United States Army 
established a missile test range here". However, the Kwajalein Test Center was 
established on 1960-10-01 and was run by the US Navy. It was transferred to the 
US Army on 1964-07-01. See 

Given that Shanks was right on the money about the 1993 change, I'm inclined to 
take Shanks's word for the 1969 change unless we find better evidence otherwise.

> ANd then additional note for Bonin Islands:
> While not part of the Southern Islands, in the period of time during
> 1952-1968, Bonin Islands were placed under American administration. It
> would probably be worth investigating whether they're following the
> Japanese time or the Mariana time or some other time standard at the time.

My guess is that they stayed on Japanese time; why switch?

> * Currently tz database say Guam stopped using local mean time at 1901 but
> a 1902 earthquake report on Guam seems to be using LMT in the report when
> compares to the time the earthquake recorded on the Philippines (the site
> note that it take times for earthquake wave to transmit and thus the time
> different between records in different place would not be identical to the
> time different)
> ** The site say Shanks used 1901 end date for LMT time for a number of
> places around the world, probably using them as placeholder. Maybe those
> 1901 end date should be nuked from tz database?

We can't simply erase instances of "1901", as we need to have a transition date. 
If we can come up with better dates we should use them. It's not entirely 
implausible that Germany introduced time zones to the Pacific in 1901, as the 
imperial government of Germany didn't obtain control of much of this area until 
1899 (at least, that's what Wikipedia says...).

> * Then in year 1959 there's a daylight saving time act passed for Guam.
> There is a table on the site that include list an link to time and order
> for implementation and cancellation of DST at Guam but the implementation
> time seems to be all over the place according to the list.

It is indeed all over the place, but the cited sources look quite official. I 
added these transitions to the proposed patch.

> The last time
> the DST was implemented in Guam according to the table seems to be 1977
> although I am not sure about the completeness of the table. If so then
> maybe a new zone for CNI would need to be created as it's after 1970 and
> the DST should be applicable to Guam only?

It's not clear whether Saipan etc. followed Guam's lead here. It would be good 
to get more data. In the meantime I'm inclined to keep the entries unsplit.

While we're on this topic I noticed that some of the former Spanish East Indies 
should have American-to-Asian transitions at the end of 1844.

Oh, and the British occupied Manila from 1762-10-06 through 1764-04. I wonder 
whether Manila switched temporarily from American to Asian time during that 
occupation? I added a comment about this.

Thanks again for all this work.
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