# Sources for Time Zone and Daylight Saving Time Data

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## Paul Eggert writes:

The public-domain tz 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 `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 GNU C Library has an independent, thread-safe implementation of a time zone file reader that is compatible with `zoneinfo`. 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.

- Date and Time Gateway is a text-based source for tables of current time throughout the world. Its point-and-click interface accesses a recent version of the tz data.
- 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.
- Local Times Around the World is a text-based system containing links to local time servers throughout the world; though the coverage is limited, the live data provide a nice way to check one's tables.
- World Time Zones contains US Naval Observatory data, used as the source for the `usno*` files.
- The United States Central Intelligence agency publishes time zone maps; 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 The pictorial quality is good, but the maps do not indicate summer time, and parts of the data are a few years out of date.
- 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 The time zone map is out of date, however.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 Facts Concerning GMT, UT, and the RGO answers questions like ``What is the difference between GMT and UTC?''
- Daylight Saving Time -- Saving Time, Saving Energy is a history of DST in the US.
- Yahoo! - Science:Measurements and Units:Time:Time Zones is where the famous Internet indexing service Yahoo! collects its time zone info.
- 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.
- Bulletins of IERS contains official publications of the International Earth Rotation Service, the committee that decides when leap seconds occur.

-- eggert@twinsun.com (1998-09-22)

## Arthur David Olson writes:

A good source of information about ISO 8601 seems to be International Standard Date and Time Notation maintained by Markus Kuhn.

-- arthur_david_olson@nih.gov (1996-01-04)