Sources for Time Zone and Daylight Saving Time Data

@(#)tz-link.htm 7.25

Please send corrections to this web page to the time zone mailing list.

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 UTC offsets and daylight-saving rules. This database (often called tz or zoneinfo) is used by several implementations, including BSD, DJGPP, GNU/Linux, HP-UX, IRIX, Solaris, and UnixWare. In the tz database's FTP distribution, the code is in the file tzcodeC.tar.gz, where C is the code's version; similarly, the data are in tzdataD.tar.gz, where D is the data's version.

The data are by no means authoritative. If you find errors, please send changes to the time zone mailing list. You can also subscribe to the mailing list, or retrieve the archive of old messages (in gzip compressed format).

The GNU C Library has an independent, thread-safe implementation of a time zone file reader that is compatible with tz. This library is freely available under the GNU Library General Public License, and is widely used in GNU/Linux systems.

The Web has several other sources for time zone and daylight saving time data. Here are some recent links that may be of interest.

Web pages using recent versions of the `tz` database

Date and Time Gateway is a text-based point-and-click interface to tables of current time throughout the world.
CGI/1.0 URL Timezone Converter is a similar interface, with source code written in Perl, using what Paul Stewart calls the "20-line hack no one will let me forget".
Local Times Around the World is a fancier web interface.
Time Zone Converter is an even fancier interface.
Burbs time zone converter is a multilingual interface.
The World Clock is a web interface to a time zone database derived from tz's.

Other `tz`-based time zone conversion software

HyperCard time zones calculator is a HyperCard stack.
Time Zone Converter is a Microsoft Windows 95/98/NT4 program.

Other time zone databases

Astrology / Astrologie -> Astrodienst Atlas Database is Astrodienst's Web version of Shanks's excellent time zone history atlases published by Astro Communications Services.
WORLDTIME: interactive atlas, time info, public holidays contains information on local time, sunrise and sunset, and public holidays in several hundred cities around the world.
World Time Zones contains US Naval Observatory data, used as the source for the usno* files in the tz distribution.
The International Air Transport Association publishes the IATA Standard Schedules Information Manual (SSIM), which gives current time zone rules for all the airports served by commercial aviation.

Maps

The United States Central Intelligence Agency publishes a time zone map; the Perry-Castañeda Library Map Collection of the University of Texas at Austin has on-line 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.
World time zones map with current time has several fancy time zone maps; it covers Russia particularly well. The maps' pictorial quality is not quite as good as the CIA's and (as usual with maps) the maps are not quite up to date.

Daylight saving time concepts and history

Daylight Saving Time -- History, rationale, laws and dates is a good overall history of DST.
The Time of Internet contains good descriptions of Time Zones and daylight saving time, with diagrams. The time zone map is out of date, however.
A few countries have well-documented histories of legal time.

Australia
The Community Relations Division of the NSW Attorney General's Department maintains a history of daylight saving in New South Wales.
Brazil
The Time Service Department of the National Observatory records Brazil's daylight saving time decrees (in Portuguese).
Germany
The National Institute for Science and Technology maintains a history of German legal time.
Israel
The Ministry of Interior periodically issues announcements (in Hebrew).
United Kingdom
History of legal time in Britain is an excellent discussion for the country with perhaps the best-documented history of clock adjustments.

Precision timekeeping

Time Server discusses the Network Time Protocol (NTP), used to synchronize clocks of Internet hosts.
A Few Facts Concerning GMT, UT, and the RGO answers questions like "What is the difference between GMT and UTC?"
Astronomical Times explains more abstruse astronomical time scales like TT, TCG, and TDB.
Earth and Its Reference Systems briefly explains interplanetary space flight timekeeping.
Bulletins of IERS contains official publications of the International Earth Rotation Service, the committee that decides when leap seconds occur.

Time notation

A Summary of the International Standard Date and Time Notation is a good summary of ISO 8601.

Sources for Time Zone and Daylight Saving Time Data

The tz database

Web pages using recent versions of the tz database

Other tz-based time zone conversion software