internet assigned numbers authority (iana) time zone database

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• How Time Zones Are Coordinated

Around this time of year, many places in the Northern Hemisphere "spring forward" into daylight saving time, moving their clocks ahead one hour to realize sunnier skies in their evening times. On different days throughout the Southern Hemisphere, many similarly wind back their clocks to brace for the winter months ahead. While this annual ritual is standard for many, some locations this year won't adopt daylight saving time as they previously did, and other places will do it differently than before.

One of the most fascinating aspects of these time changes is that for many people they are fully automatic. Billions of devices around the world will automatically change without their users lifting a finger. Airline schedules will instantly adapt, calendar invites will silently adjust. The sleep-deprived will probably see "01:59" one minute, and "03:00" the next.

How is it possible for all these changes to happen seamlessly? The Time Zone Database, part of the Internet Assigned Numbers Authority (IANA) responsibilities of ICANN, is a community collaboration that forms the foundation of this synchronicity. Let's explore how it works.

What is the Time Zone Database?

The Time Zone Database is fundamentally a machine-readable description of the time zones used in locales across the world, including when transitions to and from daylight saving time occur. It contains an exhaustive set of mathematical rules that govern these transitions. Users of computers, phones, and web applications either select their location in their time settings, or sometimes find themselves automatically geolocated, and based on that location these rules do the rest of the work.

The rules cover not just the current time, but historical time adjustments and projected adjustments in the future. The database also records leap seconds, which are small adjustments made to account for irregularities in the Earth's rotation. The formal scope of the project is to faithfully record times from the year 1970 onward, so you can find out, for example, exactly when the 1985 Live Aid concert started for someone watching from Rio de Janeiro. However, the database contains historical data from before then as well.

How is the database maintained?

While IANA hosts the project, and is responsible for distributing the data, the curation of the time zone data is performed by a community of experts and interested observers convened through an IANA discussion forum. This group evaluates reports of changes to time zone policy, assesses the provenance of any proclamations, and if an update to the database is necessary, makes sure the changes are accurately recorded.

This group is led by volunteer Time Zone Coordinators, who organize the editorial reviews and make any final adjudications based on the group's review. The entire project originated with Arthur David Olson, who served in this role for many years. Today, Dr Paul Eggert and Tim Parenti lead this group.

How are time zone policies changed?

The time zone in any given location is essentially the time that people in that area set their clocks to. The time zone database seeks to reflect this "ground truth" through documenting sufficient evidence to confirm what time people adhere to. In most situations, this ground truth is set through applicable laws and regulations, which are defined by governments.

In addition to providing a home for the database, IANA also plays an educational role for policymakers. Through ICANN's global engagement capabilities, IANA helps educate policymakers on the need to make time zone changes in a way that minimizes potential negative technical impacts.

One of the important facets of this work is recognizing that, even if the Time Zone Database is updated with a new policy, propagation of the updated data can take many months, even up to a year or two. Most devices do not immediately retrieve the updated mathematical rules directly from IANA. Instead, software vendors retrieve the data, implement the changes into their software, and then distribute it to their customers through software updates. The latest changes may not be available to you until you install the latest system update to your computer or phone.

Because of this propagation time, it is crucial that policymakers provide a year or more advance notice to IANA before changes to their time zone policies take effect. Without this lead time it is almost guaranteed there will be great confusion caused by the use of inconsistently distributed time zone data.

For most people, the fact that their devices keep up with time changes happens like magic. But it is a magic born of hard work by a group of key contributors who diligently update the time zone database. As one of the many centralized Internet coordination functions we host, it is something ICANN is proud to support, and we look to continue to facilitate into the future.

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“Time Zone King”: How One UCLA Computer Scientist Keeps Digital Clocks Ticking

UC IT Blog March 30, 2022 All Articles Engineering , IANA , Internet Assigned Numbers Authority , Samueli School of Engineering , Time , time zone , UCLA

This article originally appeared on the UCLA Samueli School of Engineering web site.

Paul Eggert may not be the most famous person from Russell, Kansas. That distinction, he says, goes to former U.S. senators Bob Dole or Arlen Specter. But this Midwestern native sure has his finger on the pulse of the most valuable commodity in the world: time. 

If you’ve ever looked at the clock on a computer, smartphone, smartwatch or practically any other digital screen — and the time has been correct — you owe Eggert, a senior lecturer of computer science at the UCLA Samueli School of Engineering, a debt of gratitude. Working quietly in his spare time, Eggert helps manage everyone else’s time across the globe’s 24 plus time zones. 

Dubbed “The Time Zone King” by  Medium’s tech site OneZero , Eggert never thought he’d be caught in the spotlight doing something he views as a hobby.

“I didn’t do this to become famous, and I don’t think I’m famous now,” Eggert said — sounding bemused by all the fuss. “It’s just a hobby. My brother does genealogy, so I know my ancestors back to the 13th century, and my hobby is time zones.”

Eggert is currently the editor and coordinator of the Time Zone Database at the Internet Assigned Numbers Authority (IANA), which is one of the internet’s oldest operational institutions. The IANA dates back to the 1970s as an unofficial body before getting funding from the U.S. Defense Advanced Research Projects Agency and coining its name in 1988.

The importance of the Time Zone Database extends beyond keeping everyone on time for Zoom meetings across the globe. Hundreds of millions of people use Eggert’s code every day regardless of whether it is daylight-saving time or if they are flying between time zones. It also enables timestamps on official documents and photos showing when they were created and modified.

What makes the thankless task for Eggert and a small team of IANA “zone keepers” even more complicated is geopolitics. That’s when governments sometimes decide to change their time zones unilaterally with just a few days’ notice. Time becomes currency for these governments looking to flex their political muscles and alter the time without properly alerting the rest of the world. 

For Eggert, who undertakes this work without pay and in between teaching computer science classes at UCLA, the complexities necessitate staying up to date via an IANA-managed mailing list and figuring out when to change the database so order can be maintained.

“Last October, it was Palestine and a couple of weeks before that it was Fiji,” Eggert said. “The bread and butter of the work and the most important part of the work is just keeping track of what governments do with their clocks.” 

And this, Eggert said, is the biggest challenge when it comes to managing the database. The codebase itself is no problem, he said, but the interests of various parties can muddy the waters and make the work unexpectedly contentious.

“Sometimes I think governments delight in proving us wrong,” Eggert said.

Though he now plays an important role in upkeeping the online world, Eggert didn’t set out on a career in computer science with the intention of pursuing such an ambitious undertaking.

“I wrote a Blackjack simulator,” Eggert said. “I was 16 years old, and I was dreaming of going to Vegas and making a killing because I’d have this computer strategy and everyone else was still doing stuff by hand. Needless to say, none of that ever happened.”

When Eggert attended Rice University in 1971, the computer science field was still new and most schools, including Rice University, didn’t have computer science departments. Eggert graduated with a bachelor’s degree in electrical engineering in 1975 and went on to get his master’s degree and Ph.D. in computer science from UCLA. 

Eggert joined the faculty at UC Santa Barbara as an assistant professor from 1980 to 1983 before embarking on a two-decade career in industry, jumping between his own startups and larger companies. It was at his second startup Twin Sun, Inc., that he first encountered the time zone database in 1991. 

“There were a bunch of network computers in the Far East, and I had to get their clocks right,” Eggert said. “And so I discovered this nascent time zone database, maintained by Arthur David Olson at the National Institutes of Health.”

Olson’s database only covered a small portion of the world’s time zones, and as Eggert began inputting those for the Far East, he figured he would fill in the rest while he was at it. 

“It’s like coin collecting or stamp collecting,” Eggert said. “You want to have all the U.S. dollars ever minted, and if you collected some of them, you’d want them all. It was sort of that attitude.”

But maintaining the time zone databases isn’t just about knowing what time it is right now. Many programs and software rely on historical data to run properly, and collecting time zone history from all corners of the world is no easy feat. Luckily, there was another group of individuals who had been profiting from doing just that for centuries: astrologers. 

Before he would eventually join the regular faculty at UCLA in 2002, Eggert headed to the university libraries and pored over old books containing data collected by fortunetellers and psychics who used the information to create astrological charts. He combed through the tables of information that documented locations and the times they observed, going all the way back to 1883 when the standard time in the U.S was introduced. 

Unfortunately, accuracy was not the primary concern of many of the astrologers who compiled this information. For them, time was a business. 

“The astrologers were focused on the rich parts of the world where people had money to cast horoscopes,” Eggert said. “I’ve been pretty firm about how I want to get rid of the biased, bogus data, but I’ve agreed to do it more gradually to give people time to adjust their old software.”

Looking into the database’s future, Eggert cautioned that it will require a coordinated effort to maintain the legitimacy and consistency of time zone recordkeeping. 

“It has to be collaborative, and it has to be institutionalized,” Eggert said. “The technical challenges are there, but the political challenges are the thing that I most want people to understand and think ahead to if we want this to keep going.”

Sara Hubbard contributed to this story.

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IANA (TZDB) time zone information

This page provides information about the IANA (also known as TZ or TZDB) time zones used in Noda Time via DateTimeZoneProviders.Tzdb . Select a time zone data version from the drop-down below to see the list of zones from that version. See the notes at the end of this page for more information.

Data version: 2024a 2023d 2023c 2023b 2023a 2022g 2022f 2022e 2022d 2022c 2022b 2022a 2021e 2021d 2021c 2021b 2021a 2020e 2020d 2020c 2020b 2020a 2019c 2019b 2019a 2018i 2018h 2018g 2018f 2018e 2018d 2018c 2017c 2017b 2017a 2016j 2016i 2016h 2016g 2016f 2016e 2016d 2016c 2016b 2016a 2015g 2015f 2015e 2015d 2015c 2015b 2015a 2014j 2014i 2014h 2014g 2014f 2014e 2014c 2014b 2014a 2013i 2013h

• IANA Version: 2024a
• Full source version ID: TZDB: 2024a (mapping: $Revision$)
• Alternative representations: JSON , tzvalidate

This page displays a single row per canonical ID. Aliases for each ID are listed in the row for that canonical ID, but don't each have their own row.

The latitude and longitude are in degrees. These are the values provided by zone.tab in IANA, and are the reference locations for the zones. However, that does not mean that finding the time zone at a particular location is as simple as finding the zone with the nearest location to the target one. See this Stack Overflow answer for more information and resources.

The offsets for each zone are the ones which are effective (in the specified version) in the interval [2000-01-01T00:00, 2040-01-01T00:00). May time zones observed a wider range of offsets earlier than the year 2000. There's nothing special about the year 2000 here; it's just an arbitrary cutoff that is likely to give enough information for most uses. Of course, using Noda Time directly you can find all the offsets ever observed.

The JSON format models the information from this web page closely, but latitude and longitude are separated out to make them easier to use programmatically.

tzdb: Time Zone Database Information

Provides an up-to-date copy of the Internet Assigned Numbers Authority (IANA) Time Zone Database. It is updated periodically to reflect changes made by political bodies to time zone boundaries, UTC offsets, and daylight saving time rules. Additionally, this package provides a C++ interface for working with the 'date' library. 'date' provides comprehensive support for working with dates and date-times, which this package exposes to make it easier for other R packages to utilize. Headers are provided for calendar specific calculations, along with a limited interface for time zone manipulations.

Documentation:

Reverse dependencies:.

Please use the canonical form https://CRAN.R-project.org/package=tzdb to link to this page.

Special Features

Vendor voice.

This article is more than 1 year old

tz database community up in arms over proposals to merge certain time zones

Handbags at 12 o'clock er, is that with or without daylight saving.

The time zone database hosted at the Internet Assigned Numbers Authority (IANA) has been updated following threats, earlier this year, of a fork over a proposal to merge time zones.

The update, the 2021b release of the tz code and date, was published over the weekend and omits some, but not all, of the issues that have caused concern in the project's mailing list.

The tz database is a hugely important resource that contains information on the world's time zones. It also attempts to keep track of historical changes since 1970. Its usage is relatively straightforward; a time zone has an offset from UTC and a set of rules governing daylight saving time (should it apply).

The system gets regular updates, the last being 2021a. These do not usually generate drama – 2021a, for example, tweaked timestamps for South Sudan.

However, a proposal to merge multiple regions that have had the same data post-1970 into a single time zone has been met with controversy amid fears that an ID cull could result in pre-1970 data becoming difficult to get hold of – as well as causing backwards-compatibility issues.

In a nutshell, put "Europe/Berlin" or "Europe/Oslo" with a pre-1970 date into the system, and out will come an answer. But the answer will be different for each option as there was a time when the two zones were different. However, as they've been the same for the past 50+ years, the proposal was to have "Europe/Oslo" simply be an alias of "Europe/Berlin" – meaning that Oslo's pre-1970 data would be effectively replaced by Berlin's.

"Why can Berlin keep its status and full history, but Oslo gets effectively deleted?" asked Java developer and maintainer of the Joda-Time classes Stephen Colebourne. "The answer is that Berlin has the greater population."

"The project leader," Colebourne told The Register , "is trying to force through a merger of time zones affecting timestamps pre-1970. Data that has been present in the database for many years is to be effectively removed."

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Describing the rationale for the move as "extremely limited," Colebourne went on to say: "No consideration is being taken of the big impacts on downstream systems – Joda-Time is particularly affected because of the way it handles links as full aliases.

"If a Joda-Time user were to adopt the proposed release, then it would no longer be possible to hold a time zone ID for Oslo, Stockholm or Amsterdam in memory – a catastrophic outcome."

The patch itself was proposed some months ago, and controversy has rumbled on ever since. Aside from a wholesale reversion of the patch, Colebourne suggested alternative approaches back in June before suggesting a fork in order to keep the time zone data as it was before.

The protests of Colebourne and other users have not completely fallen on deaf ears, and primary tz coordinator Paul Eggert announced the 2021b release over the weekend with some of the changes absent. The clock had been ticking due to daylight saving time observance being dropped in Samoa.

However, as well as changes for Samoa and Jordan, some merging of time zones still occurred, although the announcement noted "it omits most proposed changes that merged all Zones agreeing since 1970, as concerns were raised about doing too many of these changes at once."

The Register contacted Eggert for his take on the furore, but he preferred not to make a comment.

Eggert's announcement said of the merge: "This is part of a process that has been ongoing since 2013.

"This does not affect post-1970 timestamps, and timezone historians who build with 'make PACKRATDATA=backzone' should see no changes to pre-1970 timestamps."

As for Colebourne, he admitted that the battle was lost for now and blogged: "Tonight 9 of the 30 changes have been included in release 2021b. These are not the ones affecting Europe.

"Stay tuned as I try and work out how best to resolve this completely unecessary [sic] drama." ®

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We are responsible for coordinating some of the key elements that keep the Internet running smoothly. Whilst the Internet is renowned for being a worldwide network free from central coordination, there is a technical need for some key parts of the Internet to be globally coordinated, and this coordination role is undertaken by us.

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Sources for time zone and daylight saving time data

Time zone and daylight saving rules are controlled by individual governments. They are sometimes changed with little notice, and their histories and planned futures are often recorded only fitfully. Here is a summary of attempts to organize and record relevant data in this area.

The tz database

The public-domain time zone database contains code and data that represent the history of local time for many representative locations around the globe. It is updated periodically to reflect changes made by political bodies to time zone boundaries and daylight-saving rules. This database (often called zoneinfo or tz ) is used by several implementations, including the GNU C Library (used in GNU /Linux ), Android , B2G OS , Free BSD , Net BSD , Open BSD , Chromium OS , Cygwin , DJGPP , MINIX , webOS , AIX , BlackBerry 10 , iOS , macOS , Microsoft Windows , Open VMS , Oracle Database , and Oracle Solaris .

Each location in the database represents a region where all clocks keeping local time have agreed since 1970. Locations are identified by continent or ocean and then by the name of the location, which is typically the largest city within the region. For example, America/New_York represents most of the US eastern time zone; America/Phoenix represents most of Arizona, which uses mountain time without daylight saving time ( DST ); America/Detroit represents most of Michigan, which uses eastern time but with different DST rules in 1975; and other entries represent smaller regions like Starke County, Indiana, which switched from central to eastern time in 1991 and switched back in 2006. To use the database on an extended POSIX implementation set the TZ environment variable to the location's full name, e.g., TZ ="America/New_York" .

Associated with each region is a history of offsets from Universal Time ( UT ), which is Greenwich Mean Time ( GMT ) with days beginning at midnight; for time stamps after 1960 this is more precisely Coordinated Universal Time ( UTC ). The database also records when daylight saving time was in use, along with some time zone abbreviations such as EST for Eastern Standard Time in the US .

The following shell commands download the latest release's two tarballs to a GNU /Linux or similar host.

Alternatively, the following shell commands download the same release in a single-tarball format containing extra data useful for regression testing:

These commands use convenience links to the latest release of the tz database hosted by the Time Zone Database website of the Internet Assigned Numbers Authority (IANA) . Older releases are in files named tzcode V .tar.gz , tzdata V .tar.gz , and tzdb- V .tar.lz , where V is the version. Since 1996, each version has been a four-digit year followed by lower-case letter ( a through z , then za through zz , then zza through zzz , and so on). Since version 2016h, each release has contained a text file named " version " whose first (and currently only) line is the version. The releases are also available in an FTP directory via a less-secure protocol .

Alternatively, a development repository of code and data can be retrieved from GitHub via the shell command:

Since version 2012e, each release has been tagged in development repositories. Untagged commits are less well tested and probably contain more errors.

After obtaining the code and data files, see the README file for what to do next. The code lets you compile the tz source files into machine-readable binary files, one for each location. It also lets you read a tz binary file and interpret time stamps for that location.

Changes to the tz database

The tz code and data are by no means authoritative. If you find errors, please send changes to the time zone mailing list . You can also subscribe to it and browse the archive of old messages .

If your government plans to change its time zone boundaries or daylight saving rules, let the mailing list know well in advance. With less than a year's notice there is a good chance that some computer-based clocks will operate incorrectly after the change, due to delays in propagating updates to software and data. The shorter the notice, the more likely clock problems will arise.

Sources for the tz database are UTF-8 text files with lines terminated by LF , which can be modified by common text editors such as GNU Emacs , gedit , and vim . One editor has a package to simplify editing further:

• Sublime zoneinfo is a Sublime Text package for syntax highlighting tz source files.

For further information about updates, please see Procedures for Maintaining the Time Zone Database (Internet RFC 6557).

Commentary on the tz database

• The article tz database is an encyclopedic summary.
• How to Read the tz Database Source Files explains the tz database format.
• On the Timing of Time Zone Changes gives examples of problems caused by inadequate notice by governments of time zone and daylight saving rule changes.
• A literary appreciation of the Olson/Zoneinfo/tz database comments on the database's style.

Web sites using recent versions of the tz database

These are listed roughly in ascending order of complexity and fanciness.

• Time.is shows locations' time and zones in a simple format.
• TimeJones.com is a simple time zone converter.
• Date and Time Gateway lets you see the TZ values directly.
• Current Time in 1000 Places uses descriptions of the values.
• Time Zone Converter uses a pulldown menu.
• The World Clock – Worldwide lets you sort zone names and convert times.
• Time Difference calculates the current time difference between locations.
• Weather Now lists the weather too.
• The Time Now also lists weather.

Network protocols for tz data

• The Internet Engineering Task Force 's Time Zone Data Distribution Service (tzdist) working group defined TZDIST (Internet RFC 7808), a time zone data distribution service, along with CalDAV (Internet RFC 7809), a calendar access protocol for transferring time zone data by reference. The draft TZDIST Geolocate Extension lets a client determine its time zone region from its geographic location using a 'geo' URI .
• The Internet Calendaring and Scheduling Core Object Specification (iCalendar) (Internet RFC 5445) covers time zone data; see its VTIMEZONE calendar component. The iCalendar format requires specialized parsers and generators; a variant xCal (Internet RFC 6321) uses XML format, and a variant jCal (Internet RFC 7265) uses JSON format.

Other tz compilers

• Vzic is a C program that compiles tz source into iCalendar-compatible VTIMEZONE files. Vzic is freely available under the GNU General Public License ( GPL ) .
• tziCal – tz database conversion utility is like Vzic, except for the .NET framework and with a BSD -style license.
• DateTime::TimeZone contains a script parse_olson that compiles tz source into Perl modules. It is part of the Perl DateTime Project , which is freely available under both the GPL and the Perl Artistic License. DateTime::TimeZone also contains a script tests_from_zdump that generates test cases for each clock transition in the tz database.
• The Time Zone Database Parser is a C++ parser and runtime library. It is freely available under the Creative Commons Attribution 4.0 International Public License .
• International Components for Unicode ( ICU ) contains C/C++ and Java libraries for internationalization that has a compiler from tz source and from CLDR data (mentioned below ) into an ICU -specific format. ICU is freely available under a BSD -style license.
• The Tzdata package for the Elixir language downloads and compiles tz source and exposes API s for use. It is freely available under the MIT license.
• The TZUpdater tool compiles tz source into the format used by Oracle Java.
• The Java 8 java.time API can be supplemented by ThreeTen-Extra , which is freely available under a BSD -style license.
• Joda-Time – Java date and time API contains a class org.joda.time.tz.ZoneInfoCompiler that compiles tz source into a binary format. It inspired Java 8 java.time , which its users should migrate to once they can assume Java 8 or later. It is available under the Apache License .
• Time4J – Advanced date, time and interval library for Java contains a class net.time4j.tool.TimezoneRepositoryCompiler that compiles tz source into a binary format. Time4J is available under the GNU Lesser General Public License ( LGPL ) .
• ICU (mentioned above ) contains compilers and Java-based libraries.
• Noda Time – Date and time API for .NET and TZ4Net are similar to Joda-Time and Time4J, but for the .NET framework instead of Java. They are freely available under the Apache License and a BSD -style license, respectively.
• Moment Timezone is a plugin for the Moment.js date manipulation library. It is freely available under the MIT license.
• TimezoneJS.Date 's API is upward compatible with standard JavaScript Dates. It is freely available under the Apache License.
• Walltime-js translates UT to local time. It is freely available under the MIT license.
• JuliaTime contains a compiler from tz source into Julia . It is freely available under the MIT license.
• pytz – World Timezone Definitions for Python compiles tz source into Python . It is freely available under a BSD -style license.
• TZInfo – Ruby Timezone Library compiles tz source into Ruby . It is freely available under the MIT license.
• The Chronos Date/Time Library is a Smalltalk class library that compiles tz source into a time zone repository whose format is either proprietary or an XML -encoded representation.
• Tcl contains a developer-oriented parser that compiles tz source into text files, along with a runtime that can read those files. Tcl is freely available under a BSD -style license.

Other tz binary file readers

• The GNU C Library has an independent, thread-safe implementation of a tz binary file reader. This library is freely available under the LGPL and is widely used in GNU /Linux systems.
• GNOME 's GLib has a tz binary file reader written in C that creates a GTimeZone object representing sets of UT offsets. It is freely available under the LGPL .
• The BDE Standard Library 's baltzo::TimeZoneUtil component contains a C++ implementation of a binary file reader. It is freely available under the Apache License.
• CCTZ is a simple C++ library that translates between UTC and civil time and can read binary files. It is freely available under the Apache License.
• ZoneInfo.java is a tz binary file reader written in Java. It is freely available under the LGPL .
• Timezone is a JavaScript library that supports date arithmetic that is time zone aware. It is freely available under the MIT license.
• Tcl, mentioned above , also contains a tz binary file reader.
• DateTime::TimeZone::Tzfile is a tz binary file reader written in Perl. It is freely available under the same terms as Perl (dual GPL and Artistic license).
• The public-domain tz.js library contains a Python tool that converts tz binary data into JSON -format data suitable for use in its JavaScript library for time zone conversion. Dates before 1970 are not supported.
• The timezone-olson package contains Haskell code that parses and uses tz binary data. It is freely available under a BSD -style license.

Other tz -based time zone software

• FoxClocks is an extension for Google Chrome and for Mozilla Toolkit applications like Firefox and Thunderbird . It displays multiple clocks in the application window, and has a mapping interface to Google Earth . It is freely available under the GPL .
• Go programming language implementations contain a copy of a 32-bit subset of a recent tz database in a Go-specific format.
• International clock (intclock) is a clock that displays multiple time zones on GNU /Linux and similar systems. It is freely available under the GPL .
• Oracle Java contains a copy of a subset of a recent tz database in a Java-specific format.
• Time Zone is a WordPress plugin. It is freely available under a BSD -style license.
• Time Zone Master is a Microsoft Windows clock program that can automatically download, compile and use tz releases. The Basic version is free.
• VelaTerra is a macOS program. Its developers offer free licenses to tz contributors.

Other time zone databases

• Time-zone Atlas is Astrodienst's Web version of Shanks and Pottenger's time zone history atlases also published in software form by ACS-Starcrafts . These atlases are extensive but unreliable, as Shanks appears to have guessed many UT offsets and transitions. The atlases cite no sources and do not indicate which entries are guesswork.
• HP-UX has a database in its own tztab (4) format.
• Microsoft Windows has proprietary data mentioned above .
• World Time Server is another time zone database.
• World Time Zones contains data from the Time Service Department of the US Naval Observatory.
• The Standard Schedules Information Manual of the International Air Transport Association gives current time zone rules for airports served by commercial aviation.
• The United States Central Intelligence Agency ( CIA ) publishes a time zone map ; the Perry–Castañeda Library Map Collection of the University of Texas at Austin has copies of recent editions. The pictorial quality is good, but the maps do not indicate summer time, and parts of the data are a few years out of date.
• Current time around the world and standard time zones map of the world has several fancy time zone maps; it covers Russia particularly well. The maps' pictorial quality is not quite as good as the CIA 's but the maps are more up to date.
• How much is time wrong around the world? maps the difference between mean solar and standard time, highlighting areas such as western China where the two differ greatly. It's a bit out of date, unfortunately.

Time zone boundaries

Geographical boundaries between time zone regions are available from several geolocation services and other sources.

• Timezone Boundary Builder extracts Open Street Map data to build boundaries of tz regions. Its code is freely available under the MIT license, and its data entries are freely available under the Open Data Commons Open Database License . The maps' borders appear to be quite accurate.
• TZ timezones maps contains shapefiles of sets of tz regions. This includes tz_world , a shapefile for all the world's regions
• Whereonearth-timezone is in GeoJSON format (Internet RFC 7946), and combines the the tz_world shapefiles with the GeoPlanet dataset.
• GeoTimeZone is written in C# and is freely available under the MIT license.
• The latlong package is written in Go and is freely available under the Apache License.
• LatLongToTimezone , in both Java and Swift form, is freely available under the MIT license.
• For Node.js , the geo-tz module is freely available under the MIT license, and the tz-lookup module is in the public domain.
• The timezone_finder library for Ruby is freely available under the MIT license.
• What Time is It Here? applies MongoDB geospatial query operators to shapefiles' data.
• Free access via a network API, if you register a key, is provided by the GeoNames Timezone web service , the Google Maps Time Zone API , and the Time Zone Database & API . Commercial network API access is provided by AskGeo and GeoGarage . Also, an experimental server is available for the TZDIST Geolocate Extension mentioned above .
• " How to get a time zone from a location using latitude and longitude coordinates? " discusses other geolocation possibilities.
• Administrative Divisions of Countries ("Statoids") lists political subdivision data related to time zones.
• Time zone boundaries for multizone countries summarizes legal boundaries between time zones within countries.
• Manifold.net's Free Stuff for Manifold System Users includes a Manifold-format map of world time zone boundaries distributed under the GPL .
• The GeoCommunity lists several commercial sources for International Time Zones and Time Zone Data .
• A ship within the territorial waters of any nation uses that nation's time. In international waters, time zone boundaries are meridians 15° apart, except that UTC −12 and UTC +12 are each 7.5° wide and are separated by the 180° meridian (not by the International Date Line, which is for land and territorial waters only). A captain can change ship's clocks any time after entering a new time zone; midnight changes are common.

Civil time concepts and history

• A Walk through Time surveys the evolution of timekeeping.
• About Daylight Saving Time – History, rationale, laws & dates is an overall history of DST .
• Working with Time Zones contains guidelines and best practices for software applications that deal with civil time.
• A Brief History of Daylight Saving Time summarizes some of the contentious history of DST .
• A History of the International Date Line tells the story of the most important time zone boundary.
• Basic Time Zone Concepts discusses terminological issues behind time zones.

National histories of legal time

Precision timekeeping.

• The Science of Timekeeping is a thorough introduction to the theory and practice of precision timekeeping.
• NTP : The Network Time Protocol (Internet RFC 5905) discusses how to synchronize clocks of Internet hosts.
• The Precision Time Protocol ( IEEE 1588) can achieve submicrosecond clock accuracy on a local area network.
• Timezone Options for DHCP (Internet RFC 4833) specifies a DHCP option for a server to configure a client's time zone and daylight saving settings automatically.
• Astronomical Times explains more abstruse astronomical time scales like TDT , TCG , and TDB . Time Scales goes into more detail, particularly for historical variants.
• The IAU 's SOFA collection contains C and Fortran code for converting among time scales like TAI , TDB , TDT and UTC .
• Mars24 Sunclock – Time on Mars describes Airy Mean Time ( AMT ) and the diverse local time scales used by each landed mission on Mars.
• LeapSecond.com is dedicated not only to leap seconds but to precise time and frequency in general. It covers the state of the art in amateur timekeeping, and how the art has progressed over the past few decades.
• IERS Bulletins contains official publications of the International Earth Rotation and Reference Systems Service, which decides when leap seconds occur. The tz code and data support leap seconds via an optional " right " configuration, as opposed to the default " posix " configuration.
• Leap Smear discusses how to gradually adjust POSIX clocks near a leap second so that they disagree with UTC by at most a half second, even though every POSIX minute has exactly sixty seconds. This approach works with the default tz " posix " configuration, is supported by the NTP reference implementation, and is used by major cloud service providers.
• The Leap Second Discussion List covers McCarthy and Klepczynski's 1999 proposal to discontinue leap seconds , discussed further in The leap second: its history and possible future . UTC might be redefined without Leap Seconds gives pointers on this contentious issue, which was active until 2015 and could become active again.

Time notation

• A summary of the international standard date and time notation is a good summary of ISO 8601:2004 – Data elements and interchange formats – Information interchange – Representation of dates and times .
• XML Schema: Datatypes – dateTime specifies a format inspired by ISO 8601 that is in common use in XML data.
• §3.3 of Internet Message Format (Internet RFC 5322) specifies the time notation used in email and HTTP headers.
• Date and Time on the Internet: Timestamps (Internet RFC 3339) specifies an ISO 8601 profile for use in new Internet protocols.
• Date & Time Formats on the Web surveys web- and Internet-oriented date and time formats.
• The Best of Dates, the Worst of Dates covers many problems encountered by software developers when handling dates and time stamps.
• Alphabetic time zone abbreviations should not be used as unique identifiers for UTC offsets as they are ambiguous in practice. For example, in English-speaking North America " CST " denotes 6 hours behind UTC , but in China it denotes 8 hours ahead of UTC , and French-speaking North Americans prefer " HNC " to " CST ". The tz database contains English abbreviations for many time stamps; unfortunately some of these abbreviations were merely the database maintainers' inventions, and are gradually being removed.
• Numeric time zone abbreviations typically count hours east of UTC , e.g., +09 for Japan and −10 for Hawaii. However, the POSIX TZ environment variable uses the opposite convention. For example, one might use TZ =" JST -9" and TZ =" HST 10" for Japan and Hawaii, respectively. If the tz database is available, it is usually better to use settings like TZ ="Asia/Tokyo" and TZ ="Pacific/Honolulu" instead, as this should avoid confusion, handle old time stamps better, and insulate you better from any future changes to the rules. One should never set POSIX TZ to a value like "GMT-9" , though, since this would incorrectly imply that local time is nine hours ahead of UTC and the time zone is called " GMT ".
• Time and the Arts

TO_UTC_TIMESTAMP scalar function

The TO_UTC_TIMESTAMP scalar function returns a TIMESTAMP that is converted to Coordinated Universal Time from the timezone that is specified by the timezone string. TO_UTC_TIMESTAMP is a a statement deterministic function.

The schema is SYSIBM.

• Area is the English name of a continent, ocean, or the special area 'Etc'.
• Location is the English name of a location within the area; usually a city, or small island.
• America/Toronto
• Asia/Sakhalin
• Etc/UTC (which represents Coordinated Universal Time)

For complete details on the valid set of time zone names and the rules that are associated with those time zones, refer to the IANA time zone database . The database server uses version 2010c of the IANA time zone database. Contact IBM® support if a newer version of the IANA time zone database is required.

The result of the function is a timestamp with the same precision as expression , if expression is a timestamp. If expression is a DATE, the result of the function is a TIMESTAMP(0). Otherwise, the result of the function is a TIMESTAMP(6).

The result can be null; if the expression is null, the result is the null value. The timezone-expression cannot be null if a not-null value was supplied for the expression (SQLSTATE 42815).

The result is the expression , adjusted to the Coordinated Universal Time time zone from the time zone specified by the timezone-expression . If the timezone-expression returns a value that is not a time zone in the IANA time zone database, then the value of expression is returned without being adjusted.

The timestamp adjustment is done by first applying the raw offset from Coordinated Universal Time of the timezone-expression . If Daylight Saving Time is in effect at the adjusted timestamp for the time zone that is specified by the timezone-expression , then the Daylight Saving Time offset is also applied to the timestamp.

Time zones that use Daylight Saving Time have ambiguities at the transition dates. When a time zone changes from standard time to Daylight Saving Time, a range of time does not occur as it is skipped during the transition. When a time zone changes from Daylight Saving Time to standard time, a range of time occurs twice. Ambiguous timestamps are treated as if they occurred when standard time was in effect for the time zone.

• Convert the timestamp '1970-01-01 00:00:00' to the Coordinated Universal Time timezone from the 'America/Denver' timezone. The following returns a TIMESTAMP with the value '1970-01-01 07:00:00'. TO_UTC_TIMESTAMP ( TIMESTAMP '1970-01-01 00:00:00', 'America/Denver')

Convert the timestamp '1970-01-01 00:00:00' to the Coordinated Universal Time timezone from the server's timezone. The following returns a TIMESTAMP with the value '1970-01-01 07:00:00'.