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On simultaneously experiencing daylight
by Tim Parenti July 8, 2022

July 8, 2022

A friend shared an article investigating a recent claim on Reddit that earlier today, 8 July 2022, at 11:15 UTC, "99% of the world’s population" would simultaneously find themselves between dawn and dusk. This claim was soon popularized into a related claim that a similar percentage would "experience daylight" at that time. https://earthsky.org/earth/99-percent-worlds-population-receive-sunlight/ Spoiler: The original claim of 99% holds only if you use the most *technical* definition of twilight — including civil, nautical, and astronomical. In practice, most folks living in areas falling into the latter categories would perceive nighttime. But, as the article goes on to explore, however you slice it, it's still an impressive percentage of the global population "experiencing daylight" by any definition. -- Tim Parenti

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question re zone America/Punta_Arenas in Chile
by Alois Treindl July 7, 2022

July 7, 2022

In 2016, Chile introduced a new time zone for it south-most province Magallanes, and for this reason a new zone Zone America/Punta_Arenas -4:43:40 - LMT 1890 -4:42:46 - SMT 1910 Jan 10 -5:00 - -05 1916 Jul 1 -4:42:46 - SMT 1918 Sep 10 -4:00 - -04 1919 Jul 1 -4:42:46 - SMT 1927 Sep 1 -5:00 Chile -05/-04 1932 Sep 1 -4:00 - -04 1942 Jun 1 -5:00 - -05 1942 Aug 1 -4:00 - -04 1947 Apr 1 -5:00 - -05 1947 May 21 23:00 -4:00 Chile -04/-03 2016 Dec 4 -3:00 - -03 has been created. before it followed Zone America/Santiago -4:42:46 - LMT 1890 -4:42:46 - SMT 1910 Jan 10 # Santiago Mean Time -5:00 - -05 1916 Jul 1 -4:42:46 - SMT 1918 Sep 10 -4:00 - -04 1919 Jul 1 -4:42:46 - SMT 1927 Sep 1 -5:00 Chile -05/-04 1932 Sep 1 -4:00 - -04 1942 Jun 1 -5:00 - -05 1942 Aug 1 -4:00 - -04 1946 Jul 15 -4:00 1:00 -03 1946 Sep 1 # central Chile -4:00 - -04 1947 Apr 1 -5:00 - -05 1947 May 21 23:00 -4:00 Chile -04/-03 The new zone differs from zone Santiago at two points: - it does not have the 1946/47 DST - it differs from 2016 Dec 4, the reason of its creation. I wonder on which basis the 1946/47 DST was left out for Puntas_Arenas? Is that documented somewhere? The main reason why I ask: My two sources Shanks and Gabriel have always claimed that zone America/Santiago is only good for the province of Santiago, but that the rest of Chile did not have DST between 1927 and 1932. This is why in my private pre-1970 TZ extension I have an extra zone for 'rest of Chile besides Santiago' Zone America/Chile/Antofagasta -4:41:36 - LMT 1890 -4:42:46 - SMT 1910 Jan 10 # Santiago Mean Time -5:00 - -05 1916 Jul 1 -4:42:46 - SMT 1918 Sep 10 -4:00 - -04 1919 Jul 1 -4:42:46 - SMT 1927 Sep 1 -5:00 - -05 1932 Sep 1 0 follow America/Santiago which leaves out the 1927-1932 DST. It has however the 1946/47 DST. I have another zone, based on Shanks and Gabriel, for Vaparaiso, which leaves out the 1946/47 DST, but has a one-summer 1931/1932 DST. Zone America/Chile/Vina_del_Mar -4:46:16 - LMT 1890 -4:42:46 - SMT 1910 Jan 10 # Santiago Mean Time -5:00 - -05 1916 Jul 1 -4:42:46 - SMT 1918 Sep 10 -4:00 - -04 1919 Jul 1 -4:42:46 - SMT 1927 Sep 1 -5:00 - -05 1931 Sep 1 -5:00 Chile -05/-04 1932 Sep 1 -4:00 - -04 1942 Jun 1 -5:00 - -05 1942 Aug 1 -4:00 - -04 1947 Apr 1 0 follow America/Santiago Sadly, I have currently no sources for that beyond Shanks and Gabriel. We would need local newspaper archives from a non-Santiago newspaper for 1927-1932 to confirm. But it this is true, we have to assume that province Magellanes behaved like 'the rest of Chile' and not like Santiago before the split in 2016. That means that it should be: Zone America/Punta_Arenas -4:43:40 - LMT 1890 -4:42:46 - SMT 1910 Jan 10 -5:00 - -05 1916 Jul 1 -4:42:46 - SMT 1918 Sep 10 -4:00 - -04 1919 Jul 1 -4:42:46 - SMT 1927 Sep 1 -5:00 - -05 1932 Sep 1 -4:00 - -04 1942 Jun 1 -5:00 - -05 1942 Aug 1 -4:00 - -04 1947 Apr 1 -5:00 - -05 1947 May 21 23:00 -4:00 Chile -04/-03 2016 Dec 4 -3:00 - -03

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Re: [tz] Fixing GeoNames timezone errors
by dpatte July 6, 2022

July 6, 2022

I use the free geonames database in several of my projects. It is a user-contributed db, so all users are welcome to make corrections. They also have a paid version which is more heavily scrutinized for errors. ----- Original Message ----- From: Kerry Shetline via tz [mailto:tz@iana.org] To: <tz(a)iana.org> Sent: Wed, 6 Jul 2022 15:50:02 -0400 Subject: [tz] Fixing GeoNames timezone errors For those not familiar with the website, geonames.org provides a Creative Commons-licensed database of city, towns, geographic features, etc. Among other things, this DB provides latitude, longitude, and IANA timezone for millions of places around the world. The problem is I’m finding many of the timezone values provided in this DB are incorrect. This mostly seems to be caused by places with coordinates near timezone boundaries being incorrectly assigned a nearby but incorrect timezone. For example, Walpole Island, Ontario, Canada, right next to the US border, is set to America/Detroit instead of the correct value of America/Toronto. It’s at least easy to spot some errors like this, when a particular timezone is known to definitely belong to a different country, but there are many other errors at national, and state/province/prefect/etc. boundaries not so easy to spot. I was trying to create a timezone lookup based on country, state (admin level 1), and county (admin level 2) by going through the millions of entries in the database, building lists of which timezones were used where, but it quickly became apparent that the data was contaminated by many errors. Does anyone know of a more reliable source for determining the timezone of a location on Earth, either by its latitude and longitude, or by the country and other administrative hierarchy information? I’ve found downloads of shape files meant to define timezone boundaries, but they don’t seem to be very accurate. In fact, I suspect that the use of inaccurate timezone boundaries is the source of many of the errors in the Geonames DB, and that Geonames isn't even applying the help of the zone.tab file to rule out some of the errors caused by this.

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Fixing GeoNames timezone errors
by Kerry Shetline July 6, 2022

July 6, 2022

For those not familiar with the website, geonames.org provides a Creative Commons-licensed database of city, towns, geographic features, etc. Among other things, this DB provides latitude, longitude, and IANA timezone for millions of places around the world. The problem is I’m finding many of the timezone values provided in this DB are incorrect. This mostly seems to be caused by places with coordinates near timezone boundaries being incorrectly assigned a nearby but incorrect timezone. For example, Walpole Island, Ontario, Canada, right next to the US border, is set to America/Detroit instead of the correct value of America/Toronto. It’s at least easy to spot some errors like this, when a particular timezone is known to definitely belong to a different country, but there are many other errors at national, and state/province/prefect/etc. boundaries not so easy to spot. I was trying to create a timezone lookup based on country, state (admin level 1), and county (admin level 2) by going through the millions of entries in the database, building lists of which timezones were used where, but it quickly became apparent that the data was contaminated by many errors. Does anyone know of a more reliable source for determining the timezone of a location on Earth, either by its latitude and longitude, or by the country and other administrative hierarchy information? I’ve found downloads of shape files meant to define timezone boundaries, but they don’t seem to be very accurate. In fact, I suspect that the use of inaccurate timezone boundaries is the source of many of the errors in the Geonames DB, and that Geonames isn't even applying the help of the zone.tab file to rule out some of the errors caused by this.

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Re: [tz] Timezone error (Kyiv not Kiev)
by Stephen Trainor (Crookneck) July 6, 2022

July 6, 2022

Steve Summit wrote: > What end-user interfaces are there that present raw tz identifiers > for selection, and that might therefore confuse or offend users > if the spellings are culturally inappropriate? I’ve seen them shown (and have used them myself 'as-is') in multiple astronomy apps. (I double checked some apps today, and they are there.) I’ve never quite understood the "don’t show them to the user" argument. When I first became involved in using time zone data in a desktop application some years ago (via geonames and other downstream tzdata repackaging projects), from memory there was no mention of this guidance. It would be wrong to assume downstream consumers even know about it. And given that TZ IDs conspicuously pass the "duck test” it’s hardly surprising to see them making public appearances. They appear perfectly suited to show in a UI (with underscores replaced by spaces, I suppose). That said, replacing them with an anonymous identifier (e.g. 7252) would be a major negative for usability of the data (at least from a development/testing perspective). And while it would kick the problem downstream, it’s not going to eliminate it. I imagine many of the new set of downstream TZ ID-to-human readable translation errors or disputes that would undoubtedly ensue would land back on this list anyway. > As regulars well know, but newcomers may not, time zone identifiers > are just that: identifiers. True, but clearly there’s major inertia when it comes to changing them, as evidenced by the last several years of debate on K**v. So which is it? Easily mutable identifiers that users supposedly never see or human consumable ‘readable’ IDs?

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Error Correction Request: Europe/Kiev to Europe/Kyiv
by Ivanka Kvitka July 5, 2022

July 5, 2022

Hello, Please be aware that 'Kiev' is an error. The correct name is 'Kyiv'. When are you planning to correct the mistake? Please advise. Best regards, -- Iavanka Kvikta Russia is a terrorist country and I am not afraid to say it!

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tzdata comments link to an April Fools article
by Jeff Epler July 5, 2022

July 5, 2022

I was poking around and found the following in the "australiasia" file: # From Paul Eggert (2018-04-01): # The Guardian Express of Perth, Australia reported today that the # government decided to advance the clocks permanently on January 1, # 2019, from UT +08 to UT +09. The article noted that an exemption # would be made for people aged 61 and over, who "can apply in writing # to have the extra hour of sunshine removed from their area." See: # Daylight saving coming to WA in 2019. Guardian Express. 2018-04-01. # https://www.communitynews.com.au/guardian-express/news/exclusive-daylight-s… However, this article is a joke (note that it is dated April 1 and says some rather silly things). Maybe everyone was in on the joke, but I very nearly wasn't. I think it would be best if this reference were removed or if not clearly marked as humor. In the unlikely event that this actually reflects reality, perhaps a different reference could be used. Please cc: me on replies. Jeff

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the tzdb information schema
by Michael H Deckers July 4, 2022

July 4, 2022

Some recent difficulties with tzdb updates have led me to consider how they could have been avoided. • The fact that two timezones agree since 1970 is not represented independently from the data of each timezone. This leads to "update anomalies" well-known from database theory. For instance, before Africa/Khartoum switched to UTC - 02 h in 2017, Africa/Juba was a link (in the file africa) to Africa/Khartoum. After the switch, new Zone data for Africa/Juba had to appear in the file africa. Actually, Zone data for Africa/Juba had survived in the file backzone but this was overlooked, so that we had Zone data for Africa/Juba in both files africa and backzone from 2017c until 2018b, and these Zone data did not even agree. And all this happened for Africa/Juba even though civil time in Juba was not changed at all at the time. It appears that this error would not have happened if all African Zone data had been kept in the file africa (rather than in africa and in backzone) -- it was not the Zone data of Africa/Juba that had changed, but only the fact that Africa/Juba ws merged with Africa/Khartoum because their Zone data agreed since 1970. Unfortunately, this fact was not (and still is not) representable as an independently changeable item in tzdb. • Most of the Zone data currently contained in the file backzone have in earlier versions been stored in the "continental" files (africa, antarctica, asia, australasia, europe, northamerica, southamerica), and the reason why they are in backzone is that their Zone data agree with other Zone data since 1970. And since this may well change in the future, we have to keep these Zone data in backzone current. The file backzone is an integral part of the tzdb data, not just a container for additional data of lesser quality. The quality of any Zone data (and any Rule data) in tzdb should always be "to the best of our current knowledge" -- it just does not make sense to keep Zone data in tzdb that are not updated when we acquire relevant new information for them. Thus we should get rid of Zone data for Argentina/Rosario etc (or else update them); keeping data that are known to be wrong is not only useless, it is an invitation for consequential errors. • Letting derived data (such as whether two timezones should be merged because they agree since 1970) decide about the storage location of the Zone data for a timezone not only implies unnecessary data moves upon data updates, it may also disrupt commentary text and its references. Easily understandable comments (such as which facts were deduced from which document) are crucial for later updates, where the effect of a newly found document has to be determined, often after several years, and likely by a different contributor. • The fact that two timezones agree since 1970 has nothing to do with the fact that some timezones have changed their names, with the old names being kept as Links to the new names. Currently, however, Links representing one or both facts are kept in the same file backward, and cannot be distinguished. This leads to information loss and update anomalies: Currently, the file backward has a Link from Africa/Asmera to Africa/Nairobi -- the information that Asmera is an outdated spelling of Asmara can only be found in the file backzone. The name America/Virgin had been replaced by America/St_Thomas in version 95k, and this fact could be seen in the file backward until 2021a when this information was lost. It reappeared (in backzone) only in version 2021c. Keeping one type of information (spelling changes) in different locations (files backward or backzone) depending on an independent condition (that may even change over time) certainly causes unnecessary maintenance effort. While some of these points may sound like theoretical claims for normal forms as taught in computer science, my point here is only practical simplicity: each basic fact to be recorded in tzdb should have its obvious place where it is stored and where it can be looked up and updated; and updates of independent facts should be possible without mutual side effects. This appears to be a necessity for a collaborative project. Last Saturday, Paul Eggert has very nicely summarized the history and some of the guiding principles of tzdb. It is largely due to his immense work on the maintenance and evolvement of tzdb that the tzdb system was such a tremendous success in its first 30 years. As a means for the success over the next 30 years, I propose a simplification of the tzdb schema, so as to avoid the update anomalies described above, and thus decrease the maintenance burden, currently mainly shouldered by Paul. The information schema used in the fork produced by Stephen Colebourne is already much simpler, and it is apparently what is needed by several power users contributing to the widespread success of tzdb. Michael Deckers.

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Kyiv not Kiev
by Petro Ord July 2, 2022

July 2, 2022

Hello, Please be informed that your database has an error in naming Ukrainian city Kyiv. It is provided in the tz database as 'Kiev'. In June 2019 the name *Kyiv* was officially adopted by the United States Board on Geographic Names as the only correct one. Please correct the mistake Thank you

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Etc/GMT+nn and Etc/GMT-nn not working since zic 2021d
by Peter Krefting July 1, 2022

July 1, 2022

Hi! I am creating timezone data for an embedded device, and with space as a premium I run zic with the -r parameter to cut off all time change information from before the software release date, as this is not relevant for the system. Since commit 5f06f9a3182d2c2942be1b678e4defa9c7400653 (included in 2021d), this causes the Etc/GMT+xx and Etc/GMT-xx timezones not to work, they always report GMT ("-00"): ~ # TZ=Europe/Oslo date Mon Mar 21 13:08:32 CET 2022 ~ # TZ=Europe/London date Mon Mar 21 12:08:36 GMT 2022 ~ # TZ=Etc/GMT+1 date Mon Mar 21 12:08:43 -00 2022 ~ # TZ=Etc/GMT+2 date Mon Mar 21 12:08:45 -00 2022 This is particularly severe for our devices since previous versions of our software only supported UTC offsets, and these are automatically updated to these GMT+xx and GMT-xx timezones on update, so many of our customers are expected to have these zones configured. We are running with "-r cutoff -b fat", where cutoff depends on the release date, and the embedded software currenlty is using GNU libc 2.20. Reverting 5f06f9a3182d2c2942be1b678e4defa9c7400653 fixes the issue for us, but is probably not the correct approach. -- \\// Peter - http://www.softwolves.pp.se/

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