The tz database is a collaborative compilation of information about the world's time zones, primarily intended for use with computer programs and operating systems. Paul Eggert is its current editor and maintainer, with the organizational backing of ICANN. The tz database is also known as tzdata, the zoneinfo database or IANA time zone database, and occasionally as the Olson database, referring to the founding contributor, Arthur David Olson.
Its uniform naming convention for time zones, such as America/New_York and Europe/Paris, was designed by Paul Eggert. The database attempts to record historical time zones and all civil changes since 1970, the Unix time epoch. It also includes transitions such as daylight saving time, and also records leap seconds.
The tz database is published as a set of text files which list the rules and zone transitions in a human-readable format. For use, these text files are compiled into a set of platform-independent binary files—one per time zone. The reference source code includes such a compiler called zic (zone information compiler), as well as code to read those files and use them in standard application programming interfaces such as
Within the tz database, a time zone is any national region where local clocks have all agreed since 1970. This definition concerns itself first with geographic areas which have had consistent local clocks. This is different from other definitions which concern themselves with consistent offsets from a prime meridian. Therefore, each of the time zones defined by the tz database may document multiple offsets from UTC, typically including both standard time and daylight saving time.
In the time zone text files, each time zone has one or more "zone lines" in one of the time zone text files. The first zone line for a time zone gives the name of the time zone; any subsequent zone lines for that time zone leave the name blank, indicating that they apply to the same zone as the previous line. Each zone line for a zone specifies, for a range of date and time, the offset to UTC for standard time, the name of the set of rules that govern daylight saving time (or a hyphen if standard time always applies), the format for time zone abbreviations, and, for all but the last zone line, the date and time at which the range of date and time governed by that line ends.
The rules for daylight saving time are specified in named rule sets. Each rule set has one or more rule lines in the time zone text files. A rule line contains the name of the rule set to which it belongs, the first year in which the rule applies, the last year in which the rule applies (or "only" if it applies only in one year or "max" if it is the rule currently in effect), the type of year to which the rule applies ("-" if it applies to all years in the specified range, which is almost always the case, otherwise a name used as an argument to a script that indicates whether the year is of the specified type), the month in which the rule takes effect, the day on which the rule takes effect (which could either be a specific day or a specification such as "the last Sunday of the month"), the time of day at which the rule takes effect, the amount of time to add to the offset to UTC when the rule is in effect, and the letter or letters to use in the time zone abbreviation (for example, "S" if the rule governs standard time and "D" if it governs daylight saving time).
The time zones have unique names in the form "Area/Location", e.g. "America/New_York". A choice was also made to use English names or equivalents, and to omit punctuation and common suffixes. The underscore character is used in place of spaces. Hyphens are used where they appear in the name of a location. The Area and Location names have a maximum length of 14 characters.
The oceans are included since some islands are hard to connect to a certain continent. Some are geographically connected to one continent and politically to another. See also Boundaries between continents.
The special area of "Etc" is used for some administrative zones, particularly for "Etc/UTC" which represents Coordinated Universal Time. In order to conform with the POSIX style, those zone names beginning with "Etc/GMT" have their sign reversed from the standard ISO 8601 convention. In the "Etc" area, zones west of GMT have a positive sign and those east have a negative sign in their name (e.g "Etc/GMT-14" is 14 hours ahead of GMT.)
Location is the name of a specific location within the area – usually a city or small island.
Country names are not used in this scheme, primarily because they would not be robust, owing to frequent political and boundary changes. The names of large cities tend to be more permanent. However, the database maintainers attempt to include at least one zone for every ISO 3166-1 alpha-2 country code, and a number of user interfaces to the database take advantage of this. Additionally there is a desire to keep locations geographically compact so that any future time zone changes do not split locations into different time zones.
Usually the most populous city in a region is chosen to represent the entire time zone, although other cities may be selected if they are more widely known or result in a less ambiguous name. In the event that the name of the location used to represent the time zone changes, the convention is to create an alias in future editions so that both the old and new names refer to the same database entry.
In some cases the Location is itself represented as a compound name, for example the time zone "America/Indiana/Indianapolis". Three-level names include those under "America/Argentina/...", "America/Kentucky/...", "America/Indiana/...", and "America/North_Dakota/...".
The location selected is representative for the entire area.
|America/Costa_Rica||name of country used because the name of the largest city (and capital city) San José is ambiguous|
|America/New_York||Space replaced with underscore|
|Asia/Kolkata||name of city of Kolkata used, because it was the most populous city in the zone at the time the zone was set up, though this is no longer true|
|Asia/Sakhalin||name of island used, because largest city, Yuzhno-Sakhalinsk, has more than 14 characters|
|America/Bahia_Banderas||name of largest city altered, "de" removed from Bahia de Banderas, because correct name has more than 14 characters|
|Antarctica/DumontDUrville||the apostrophe is removed. The space would normally be replaced with "_", but the name would then exceed 14 characters.|
These are rule lines for the standard United States daylight saving time rules, rule lines for the daylight saving time rules in effect in the US Eastern Time Zone (called "NYC" as New York City is the city representing that zone) in some years, and zone lines for the America/New_York time zone, as of release version tzdata2011n of the time zone database. The zone and rule lines reflect the history of DST in the United States.
# Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S Rule US 1918 1919 - Mar lastSun 2:00 1:00 D Rule US 1918 1919 - Oct lastSun 2:00 0 S Rule US 1942 only - Feb 9 2:00 1:00 W # War Rule US 1945 only - Aug 14 23:00u 1:00 P # Peace Rule US 1945 only - Sep 30 2:00 0 S Rule US 1967 2006 - Oct lastSun 2:00 0 S Rule US 1967 1973 - Apr lastSun 2:00 1:00 D Rule US 1974 only - Jan 6 2:00 1:00 D Rule US 1975 only - Feb 23 2:00 1:00 D Rule US 1976 1986 - Apr lastSun 2:00 1:00 D Rule US 1987 2006 - Apr Sun>=1 2:00 1:00 D Rule US 2007 max - Mar Sun>=8 2:00 1:00 D Rule US 2007 max - Nov Sun>=1 2:00 0 S .... # Rule NAME FROM TO TYPE IN ON AT SAVE LETTER Rule NYC 1920 only - Mar lastSun 2:00 1:00 D Rule NYC 1920 only - Oct lastSun 2:00 0 S Rule NYC 1921 1966 - Apr lastSun 2:00 1:00 D Rule NYC 1921 1954 - Sep lastSun 2:00 0 S Rule NYC 1955 1966 - Oct lastSun 2:00 0 S # Zone NAME GMTOFF RULES FORMAT [UNTIL] Zone America/New_York -4:56:02 - LMT 1883 Nov 18 12:03:58 -5:00 US E%sT 1920 -5:00 NYC E%sT 1942 -5:00 US E%sT 1946 -5:00 NYC E%sT 1967 -5:00 US E%sT
For each time zone that has multiple offsets (usually due to daylight saving time), the tz database records the exact moment of transition. The format can accommodate changes in the dates and times of transitions as well. Zones may have historical rule changes going back many decades (as shown in the example above).
The file zone.tab is in the public domain and lists the zones. Columns and row sorting are described in the comments of the file, as follows:
# This file contains a table with the following columns: # 1. ISO 3166 2-character country code. See the file `iso3166.tab'. # 2. Latitude and longitude of the zone's principal location # in ISO 6709 sign-degrees-minutes-seconds format, # either +-DDMM+-DDDMM or +-DDMMSS+-DDDMMSS, # first latitude (+ is north), then longitude (+ is east). # 3. Zone name used in value of TZ environment variable. # 4. Comments; present if and only if the country has multiple rows. # # Columns are separated by a single tab. # The table is sorted first by country, then an order within the country that # (1) makes some geographical sense, and # (2) puts the most populous zones first, where that does not contradict (1).
Data before 1970 aims to be correct for the city identifying the region, but is not necessarily correct for the entire region. This is because new regions are created only as required to distinguish clocks since 1970.
For example, between 1963-10-23 and 1963-12-09 in Brazil only the states of Minas Gerais, Espirito Santo, Rio de Janeiro, and São Paulo had summer time. However, a requested split from America/Sao_Paulo was rejected in 2010 with the reasoning that, since 1970, the clocks were the same in the whole region.
There are two zones that cover an area that was covered by two countries after 1970. The database follows the definitions of countries as per ISO 3166-1, whose predecessor, ISO 3166, was first published in 1974.
The tz reference code and database is maintained by a group of volunteers. Arthur David Olson makes most of the changes to the code, and Paul Eggert to the database. Proposed changes are sent to the tz mailing list, which is gatewayed to the comp.time.tz Usenet newsgroup. Source files are distributed via the IANA FTP server. Typically, these files are taken by a software distributor like Debian, compiled, and then the source and binaries are packaged as part of that distribution. End users can either rely on their software distribution's update procedures, which may entail some delay, or obtain the source directly and build the binary files themselves. The IETF has published RFC 6557, "Procedures for Maintaining the Time Zone Database" documenting best practices based on similar principles.
Geographical boundaries in the form of coordinate sets are not part of the tz database, but boundaries are published by Eric Muller in the form of vector polygons. Using these vector polygons, one can determine, for each place on the globe, the tz database zone in which it is located.
The Unicode Common Locale Data Repository (CLDR) refers to zones in the tz database. However, as the name for a zone can change from one tz database release to another, the CLDR assigns the UN/LOCODE for the city used in the name for the zone, or an internally-assigned code if there is no such city for the zone, to a tzdb zone.
The tz database is used for time zone processing and conversions in many computer software systems, including:
The Olson timezone IDs are also used by the Unicode Common Locale Data Repository (CLDR) and International Components for Unicode (ICU). For example, the CLDR Windows–Tzid table maps Microsoft Windows time zone IDs to the standard Olson names, although such a mapping cannot be perfect because the number of time zones in Windows systems is significantly lower that those in the IANA TZ database.
The project's origins go back to 1986 or earlier.
On September 30, 2011, a lawsuit, Astrolabe, Inc. v. Olson et al., was filed concerning copyright in the database. As a result, on October 6, 2011, the database's mailing list and FTP site were shut down. The case revolved around the database maintainers' use of The American Atlas, by Thomas G. Shanks, and The International Atlas, by Thomas G. Shanks and Rique Pottenger. It complained of unauthorised reproduction of atlas data in the timezone mailing list archive and in some auxiliary link collections maintained with the database, though it did not actually point at the database itself. The complaint related only to the compilation of historical timezone data, and did not cover current tzdata world timezone tables.
This lawsuit was resolved on February 22, 2012 after the involvement of the Electronic Frontier Foundation, when Astrolabe voluntarily moved to dismiss the lawsuit without having ever served the defendants and agreed to a covenant not to sue in the future.
ICANN took responsibility for the maintenance of the database on October 14, 2011. The full database and a description of current and future plans for its maintenance are available online from IANA.
Iran Standard Time (IRST) or Iran Time (IT) is the time zone used in Iran. Iran uses a UTC offset UTC+03:30. IRST is defined by the 52.5 degrees east meridian, the same meridian which defines the Iranian calendar and is the official meridian of Iran.
Between 2005 and 2008, by decree of President Mahmoud Ahmadinejad, Iran did not observe daylight saving time (called Iran Daylight Time or IRDT). It was reintroduced from 21 March 2008.List of UTC time offsets
This is a list of the UTC time offsets, showing the difference in hours and minutes from Coordinated Universal Time (UTC), from the westernmost (−12:00) to the easternmost (+14:00). It includes countries and regions that observe them during standard time or year-round.
The main purpose of this page is to list the standard time offsets of different countries, territories and regions. Information on daylight saving time or historical changes in offsets can be found in the individual offset articles (e.g. UTC+01:00), or the country-specific time articles (e.g. Time in Russia).
Places that observe daylight saving time (DST) during their respective summer periods are listed only once, at the offset for their winter (usually known as "standard") period; see their individual articles for more information. A source for detailed DST and historical information is the tz database. Note that there are many instances of unofficial observation of a different offset (and/or DST) than expected by areas close to borders, usually for economic reasons.In the section names, the letter after the offset is that used in nautical time. If present, a dagger (†) indicates the usage of a nautical time zone letter outside of the standard geographic definition of that time zone.
Some locations use the term GMT (Greenwich Mean Time) instead of UTC in their definition of local time. (For most purposes, including this article, this distinction is not significant; see the UTC article for details.)
Some zones that are north/south of each other in the mid Pacific differ by 24 hours in time – they have the same time of day but dates that are one day apart. The two extreme time zones on Earth (both in the mid Pacific) differ by 26 hours.
In the following list, only the rightmost indent of a group of locations is meant to indicate the area observing the offset; the places above and to the left are meant solely to indicate the area's parent administrative divisions. For example, the entry of Eucla explains that Eucla observes the specified time offset, and the state (Western Australia) and country (Australia) are shown only for reference and are not meant to be wholly included as observing that offset.
The purpose of the "principal cities" list at the top of some of the time zone entries is to give a brief list of major cities. These should be limited to a maximum of one city per country (within each zone), and not all countries in a zone need to have a city listed. Similarly, time zones need not have any cities listed if there are no major cities in that offset.List of tz database time zones
This is a list of time zones from release 2017c of the tz database.Lists of time zones
List of time zones by country – sorted by number of current time zones in the world
List of time zones by UTC offset – current UTC offsets
List of time zone abbreviations – abbreviations
List of tz database time zones – zones used by many computer systems as defined by IANA
List of military time zonesCountry-specific:
List of time zones by U.S. stateTime in Alaska
Alaska is covered by two time zones, as described below:
Islands west of -169.5° (169°30'W) are in the Hawaii–Aleutian Time Zone (UTC−10:00, DST UTC−09:00). Daylight saving time (DST) is observed.
The town of Hyder, because it essentially is a single town split by the US-Canada border with roads only to Canada, unofficially observes Pacific Time including DST (UTC−08:00, DST UTC−07:00) like its neighbor Stewart, British Columbia, with the exception of the U.S. Post Office (because it is a federal facility).
The rest of the state is in the Alaska Time Zone and observes DST (UTC−09:00, DST UTC−08:00).Time in Angola
All of Angola uses UTC+01:00 (West Africa Time), and has never observed Daylight saving time.Time in Antarctica
Antarctica sits on every line of longitude, due to the South Pole being situated near the middle of the continent. Theoretically Antarctica would be located in all time zones; however, areas south of the Antarctic Circle experience extreme day-night cycles near the times of the June and December solstices, making it difficult to determine which time zone would be appropriate. For practical purposes time zones are usually based on territorial claims; however, many stations use the time of the country they are owned by or the time zone of their supply base (e.g. McMurdo Station and Amundsen–Scott South Pole Station use New Zealand time due to their main supply base being Christchurch, New Zealand). Nearby stations can have different time zones, due to their belonging to different countries. Many areas have no time zone since nothing is decided and there are not even any temporary settlements that have any clocks. They are simply labeled with UTC time.Time in Argentina
Argentina is located at a longitude that would naturally put it in the UTC−04:00 or UTC−05:00 time zone; however, it actually uses the UTC−03:00 time zone. Argentina determines whether to observe daylight saving time on a year-by-year basis, and individual provinces may opt out of the federal decision. At present, Argentina does not observe daylight saving time.The Argentine Hydrographic Service maintains the official national time.Time in Arizona
Time in Arizona, as in all US states, is regulated by the United States Department of Transportation.Arizona is in the Mountain Time Zone and most of the state remains in Mountain Standard Time (MST) all year.Time in Florida
Most of Florida is in the Eastern Time Zone (UTC−05:00, DST UTC−04:00).
The following parts of the Florida panhandle in northwest Florida are in the Central Time Zone (UTC−06:00, DST UTC−05:00):
Santa Rosa County
Northern part of Gulf CountyDaylight saving time is observed throughout the state.Time in Germany
The time zone in Germany is Central European Time (Mitteleuropäische Zeit, MEZ; UTC+01:00) and Central European Summer Time (Mitteleuropäische Sommerzeit, MESZ; UTC+02:00). Daylight saving time is observed from the last Sunday in March (02:00 CET) to the last Sunday in October (03:00 CEST). The doubled hour during the switch back to standard time is named 2A (02:00 to 03:00 CEST) and 2B (02:00 to 03:00 CET).Time in Idaho
The U.S. state of Idaho is covered by two time zones, as described below. All locations observe daylight saving time.
The Pacific Time Zone (UTC−08:00, DST UTC−07:00) covers an area roughly coterminous with the Idaho Panhandle or North Idaho:
Kootenai County (includes Coeur d'Alene)
Latah County (includes Moscow)
Nez Perce County (includes Lewiston)
Portion of Idaho County north of the Salmon River
The towns of Burgdorf and WarrenAn easy way to distinguish the line is that it essentially follows the line that divides Washington and Oregon. If a county in Idaho is due east of Washington, it's Pacific Time. On the other hand, the counties of Idaho that are fully due east of Oregon are on Mountain Time.
The Mountain Time Zone (UTC−07:00, DST UTC−06:00) covers the rest of the state.Time in Indiana
The U.S. state of Indiana is divided between Eastern and Central time zones. The official dividing line has generally moved progressively west from its original location on the Indiana–Ohio border, to a position dividing Indiana down the middle, and finally to its current location along much of the Indiana–Illinois border. In April 2006, several southwestern and northwestern counties reverted to Central time, although by late 2007 all but two had returned to Eastern time.
As Indiana is on the western frontier of the Eastern time zone, there was opposition from many in the state to observing daylight saving time for decades. The 2005 decision by the Indiana General Assembly to implement daylight saving time state-wide beginning in April 2006 remains controversial.Time in Kazakhstan
Standard time in Kazakhstan is either UTC+05:00 or UTC+06:00. These times apply throughout the year as Kazakhstan does not observe Daylight saving time.Time in Russia
There are eleven time zones in Russia, which currently observe times ranging from UTC+02:00 to UTC+12:00. Daylight saving time is not used in Russia (since March 2011).Yakutsk (disambiguation)
Yakutsk is the capital of the Sakha Republic, Russia.
Yakutsk may also refer to:
Yakutsk Urban Okrug, a municipal formation in the Sakha Republic, Russia, which the city of Yakutsk and eleven rural localities in its jurisdiction are incorporated as
Yakutsk Airport, an airport in the Sakha Republic, Russia
Yakutsk Time, a time zone in Russia, ten hours ahead of UTC
Asia/Yakutsk, a time zone identifier in the Tz database
|UTC offset for standard time and |
Daylight saving time (DST)
Italics: historical or unofficial
|Time zone data sources|
|Lists of time zones|