On Jan 20, 2025, at 7:17 PM, Patrick BENNY via tz <tz@iana.org> wrote:
> I understood now that the data is as intended, and the comment does help to
> understand the reason. I was first alerted about this because a reverse
> lookup of the Asia/Tokyo timezone until now returned only Japan, but started
> evaluating as Australia.
Any reverse lookup that returns just "Australia" for Asia/Tokyo is broken. It
should return both Japan and Australia.
> It definitely is an interesting fact that Asia/Tokyo is traditionally
> observed in a country other than Japan.
A tzdb timezone is not necessarily associated with a single country.
"Asia/Tokyo" doesn't mean "Tokyo time"; it means "any location that, from 1970
to the present, has the same offset from UTC and the same time-adjustment rules
as in Tokyo". Presumably the Eyre Bird Observatory region is such a location,
the fact that it's not in Japan notwithstanding:
https://www.abc.net.au/news/2024-11-22/outback-wa-properties-strange-time-zones/104542494
As "Theory and pragmatics of the tz code and data":
https://data.iana.org/time-zones/theory.html
says:
The tz database attempts to record the history and predicted future of
civil time scales. It organizes time zone and daylight saving time data by
partitioning the world into timezones whose clocks all agree about timestamps
that occur after the POSIX Epoch (1970-01-01 00:00:00 UTC). Although 1970 is a
somewhat-arbitrary cutoff, there are significant challenges to moving the
cutoff earlier even by a decade or two, due to the wide variety of local
practices before computer timekeeping became prevalent. Most timezones
correspond to a notable location and the database records all known clock
transitions for that location; some timezones correspond instead to a fixed UTC
offset.
Each timezone typically corresponds to a geographical region that is
smaller than a traditional time zone, because clocks in a timezone all agree
after 1970 whereas a traditional time zone merely specifies current standard
time. For example, applications that deal with current and future timestamps in
the traditional North American mountain time zone can choose from the timezones
America/Denver which observes US-style daylight saving time (DST), and
America/Phoenix which does not observe DST. Applications that also deal with
past timestamps in the mountain time zone can choose from over a dozen
timezones, such as America/Boise, America/Edmonton, and America/Hermosillo,
each of which currently uses mountain time but differs from other timezones for
some timestamps after 1970.
Clock transitions before 1970 are recorded for location-based
timezones, because most systems support timestamps before 1970 and could
misbehave if data entries were omitted for pre-1970 transitions. However, the
database is not designed for and does not suffice for applications requiring
accurate handling of all past times everywhere, as it would take far too much
effort and guesswork to record all details of pre-1970 civil timekeeping.
Although some information outside the scope of the database is collected in a
file backzone that is distributed along with the database proper, this file is
less reliable and does not necessarily follow database guidelines.
That location has a bit more history:
https://eyrebirds.org.au/history/
but I don't know when that time zone was officially established; the
Observatory was established in 1977 or so, but I don't know what time zones
prevailed *prior* to that.
The time zone there may be unofficial, but if we're considering unofficial time
zones, apparently, as per the ABC story, there's another unofficial time zone
in the region:
A number of outposts along the Eyre Highway, including Cocklebiddy,
have long operated on the unofficial Central Western Time, which is 45 minutes
ahead of the official Western Standard Time (WST).
"It doesn't make much difference to us here, but it is a good
conversation point," Cocklebiddy Roadhouse manager Laree Bastin says.
However, to the confusion of visitors, the Eyre Bird Observatory (EBO)
operates another 15 minutes ahead of Central Western Time.
EBO committee member Steve Edwards says he has never been given a clear
explanation.
"The only answer I've got is that it is much easier for all concerned
to make EBO time one hour ahead of Perth," he says.
Anybody know the history of either of those, including any DST rules? Western
Standard Time appears to have had DST in the 1970s up to 2009.
