<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>Sources for Time Zone and Daylight Saving Time Data</title> <link rel="schema.DC" href="http://purl.org/DC/elements/1.1/"> <meta http-equiv="Content-type" content='text/html; charset="UTF-8"'> <meta name="DC.Creator" content="Eggert, Paul"> <meta name="DC.Contributor" content="Olson, Arthur David"> <meta name="DC.Date" content="2015-01-29"> <meta name="DC.Description" content="Sources of information about time zones and daylight saving time"> <meta name="DC.Identifier" content="http://www.iana.org/time-zones/repository/tz-link.htm"> <meta name="Keywords" content="database,daylight saving,DST,time zone,timezone,tz,zoneinfo"> </head> <body> <h1>Sources for Time Zone and Daylight Saving Time Data</h1> <h2>The <code><abbr title="time zone">tz</abbr></code> database</h2> <p> The <a href="http://en.wikipedia.org/wiki/Public_domain">public-domain</a> 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 <a href="http://en.wikipedia.org/wiki/Time_zone">time zone</a> boundaries and <a href="http://en.wikipedia.org/wiki/Daylight_saving_time">daylight-saving</a> rules. This database (often called <code>zoneinfo</code> or <code><abbr>tz</abbr></code>) is used by several implementations, including <a href="http://www.gnu.org/software/libc/">the <abbr title="GNU's Not Unix">GNU</abbr> C Library</a> (used in <a href="http://en.wikipedia.org/wiki/Linux"><abbr>GNU</abbr>/Linux</a>), <a href="http://www.android.com">Android</a>, <a href="https://developer.mozilla.org/en-US/Firefox_OS">Firefox <abbr title="Operating System">OS</abbr></a>, <a href="https://www.freebsd.org">Free<abbr title="Berkeley Software Distribution">BSD</abbr></a>, <a href="http://netbsd.org">Net<abbr>BSD</abbr></a>, <a href="http://openbsd.org">Open<abbr>BSD</abbr></a>, <a href="https://cygwin.com">Cygwin</a>, <a href="http://www.delorie.com/djgpp/"><abbr title="DJ's GNU Programming Platform">DJGPP</abbr></a>, <a href="http://en.wikipedia.org/wiki/MINIX">MINIX</a>, <a href="http://en.wikipedia.org/wiki/WebOS"><abbr title="Web Operating System">webOS</abbr></a>, <a href="http://ibm.com/aix"><abbr title="Advanced Interactive eXecutive">AIX</abbr></a>, <a href="http://en.wikipedia.org/wiki/BlackBerry_10">BlackBerry 10</a>, <a href="http://www.apple.com/ios/"><abbr title="iPhone OS">iOS</abbr></a>, <a href="http://windows.microsoft.com">Microsoft Windows</a>, <a href="http://h71000.www7.hp.com">Open<abbr title="Virtual Memory System">VMS</abbr></a>, <a href="https://www.oracle.com/database/index.html">Oracle Database</a>, <a href="http://oracle.com/solaris">Oracle Solaris</a>, and <a href="http://www.apple.com/osx/"><abbr title="Operating System Ten">OS X</abbr></a>.</p> <p> 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, <code>America/New_York</code> represents most of the <abbr title="United States">US</abbr> eastern time zone; <code>America/Phoenix</code> represents most of Arizona, which uses mountain time without daylight saving time (<abbr title="daylight saving time">DST</abbr>); <code>America/Detroit</code> represents most of Michigan, which uses eastern time but with different <abbr>DST</abbr> 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 <a href="http://en.wikipedia.org/wiki/POSIX"><abbr title="Portable Operating System Interface">POSIX</abbr></a> implementation set the <code><abbr>TZ</abbr></code> environment variable to the location's full name, e.g., <code><abbr>TZ</abbr>="America/New_York"</code>.</p> <p> Associated with each region is a history of offsets from <a href="http://en.wikipedia.org/wiki/Universal_Time">Universal Time</a> (<abbr>UT</abbr>), which is <a href="http://en.wikipedia.org/wiki/Greenwich_Mean_Time">Greenwich Mean Time</a> (<abbr>GMT</abbr>) with days beginning at midnight; for time stamps after 1960 this is more precisely <a href="http://en.wikipedia.org/wiki/Coordinated_Universal_Time">Coordinated Universal Time</a> (<abbr>UTC</abbr>). The database also records when daylight saving time was in use, along with alphabetic time zone abbreviations such as <abbr>EST</abbr> for Eastern Standard Time in the <abbr>US</abbr>.</p> <p> In the <code><abbr>tz</abbr></code> database's <a href="ftp://ftp.iana.org/tz/releases/"><abbr title="File Transfer Protocol">FTP</abbr> releases</a> the code is in the file <code>tzcode<var>C</var>.tar.gz</code>, where <code><var>C</var></code> is the code's version; similarly, the data entries are in <code>tzdata<var>D</var>.tar.gz</code>, where <code><var>D</var></code> is the data's version. Since 1996, each version has been a four-digit year followed by lower-case letter (<samp>a</samp> through <samp>z</samp>, then <samp>za</samp> through <samp>zz</samp>, then <samp>zza</samp> through <samp>zzz</samp>, and so on). Convenience links to the <a href="ftp://ftp.iana.org/tz/tzcode-latest.tar.gz">latest code</a> and <a href="ftp://ftp.iana.org/tz/tzdata-latest.tar.gz">latest data</a> revisions are also available. The following <a href="http://en.wikipedia.org/wiki/Unix_shell">shell</a> commands download these files to a <abbr>GNU</abbr>/Linux or similar host; see the downloaded <code>README</code> file for what to do next.</p> <pre style="margin-left: 2em"><code>mkdir tz cd tz <a href="http://www.gnu.org/software/wget/">wget</a> --retr-symlinks 'ftp://ftp.iana.org/tz/tz*-latest.tar.gz' <a href="http://www.gnu.org/software/gzip/">gzip</a> -dc tzcode-latest.tar.gz | <a href="http://www.gnu.org/software/tar/">tar</a> -xf - gzip -dc tzdata-latest.tar.gz | tar -xf - </code></pre> <p> The code and data files can also be obtained from the <a href="http://www.iana.org/time-zones">Time Zone Database website</a> of the <a href="http://www.iana.org">Internet Assigned Numbers Authority (IANA)</a>. An <a href="https://github.com/eggert/tz">unofficial development repository</a> of the code and data is available in <a href="http://git-scm.com">Git</a> form from <a href="https://github.com">GitHub</a>; be careful, as this repository is less well tested and probably contains more errors. <p> The code lets you compile the <code><abbr>tz</abbr></code> source files into machine-readable binary files, one for each location. It also lets you read a <code><abbr>tz</abbr></code> binary file and interpret time stamps for that location.</p> <p> The files are by no means authoritative. If you find errors, please send changes to the <a href="mailto:tz@iana.org">time zone mailing list</a>. You can also <a href="http://news.gmane.org/gmane.comp.time.tz">browse recent messages</a> sent to the mailing list, <a href="https://mm.icann.org/mailman/listinfo/tz">subscribe</a> to it, and browse the <a href="http://mm.icann.org/pipermail/tz/">archive of old messages</a>. For further information about updates, please see <a href="http://tools.ietf.org/html/rfc6557">Procedures for Maintaining the Time Zone Database</a> (Internet <abbr title="Request For Comments">RFC</abbr> 6557).</p> <p> The Web has several other sources for time zone and daylight saving time data. Here are some links that may be of interest. </p> <h2>Commentary on the <code><abbr>tz</abbr></code> database</h2> <ul> <li>The article <a href="http://en.wikipedia.org/wiki/Tz_database">tz database</a> is an encyclopedic summary.</li> <li><a href="http://www.cstdbill.com/tzdb/tz-how-to.html">How to Read the tz Database Source Files</a> explains the <code><abbr>tz</abbr></code> database format.</li> <li><a href="http://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonzoneinfotz-database/">A literary appreciation of the Olson/Zoneinfo/tz database</a> comments on the database's style.</li> </ul> <h2>Web sites using recent versions of the <code><abbr>tz</abbr></code> database</h2> <p> These are listed roughly in ascending order of complexity and fanciness. </p> <ul> <li><a href="http://time.is">Time.is</a> shows locations' time and zones in a simple format.</li> <li><a href="http://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a> lets you see the <code><abbr>TZ</abbr></code> values directly.</li> <li><a href="http://convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current Time in 1000 Places</a> uses descriptions of the values.</li> <li><a href="http://www.timezoneconverter.com/cgi-bin/tzc.tzc">Time Zone Converter</a> uses a pulldown menu.</li> <li><a href="http://home.kpn.nl/vanadovv/time/TZworld.html">Complete timezone information for all countries</a> displays tables of DST rules. <li><a href="http://timeanddate.com/worldclock/">The World Clock – Time Zones</a> lets you sort zone names and convert times.</li> <li><a href="http://permatime.com">Permatime</a> generates and views links that refer to a particular point in time and can be displayed in multiple time zones.</li> <li><a href="http://www.zeitverschiebung.net/en/">Time Difference</a> calculates the current time difference between locations.</li> <li><a href="http://www.wx-now.com">Weather Now</a> lists the weather too.</li> <li><a href="http://worldtime.io">worldtime.io</a> also contains data about time zone boundaries; it supports queries via place names and shows location maps.</li> </ul> <h2>Network protocols for <code><abbr>tz</abbr></code> data</h2> <ul> <li>The <a href="http://www.ietf.org">Internet Engineering Task Force</a>'s <a href="http://datatracker.ietf.org/wg/tzdist/charter/">Time Zone Data Distribution Service (tzdist) working group</a> is developing a scalable protocol for distributing time zone data to clients. It has generated a a <a href="http://datatracker.ietf.org/doc/draft-ietf-tzdist-service/">draft protocol for transferring time zone data</a> and a <a href="http://datatracker.ietf.org/doc/draft-ietf-tzdist-caldav-timezone-ref/">draft protocol for transferring time zone data by reference</a>. This work is based on the iCalendar and CalConnect efforts described below.</li> <li>The <a href="http://tools.ietf.org/html/rfc5545"> Internet Calendaring and Scheduling Core Object Specification (iCalendar)</a> (Internet <abbr>RFC</abbr> 5445) covers time zone data; see its VTIMEZONE calendar component. The iCalendar format requires specialized parsers and generators; a variant <a href="http://tools.ietf.org/html/rfc6321">xCal</a> (Internet <abbr>RFC</abbr> 6321) uses <a href="http://www.w3.org/XML/"><abbr title="Extensible Markup Language">XML</abbr></a> format, and a variant <a href="http://tools.ietf.org/html/rfc7265">jCal</a> (Internet <abbr>RFC</abbr> 7265) uses <a href="http://www.json.org"><abbr title="JavaScript Object Notation">JSON</abbr></a> format. <a href="http://calconnect.org">CalConnect, The Calendaring and Scheduling Consortium</a> is promoting further work in this area. <a href="http://calconnect.org/publications/icalendartimezoneproblemsandrecommendationsv1.0.pdf">iCalendar TIMEZONE Problems and Recommendations</a> offers guidelines and recommendations for the use of VTIMEZONE and <code><abbr>tz</abbr></code>.</li> <li>The <a href="http://calconnect.org/publications/timezoneregistryandservicerecommendationsv1.0.pdf">Timezone Registry and Service Recommendations</a> of CalConnect's <a href="http://calconnect.org/tc-timezone.shtml">TIMEZONE Technical Committee</a> discusses a strategy for defining and deploying a time zone registration process that would establish unique names for each version of each <code><abbr>tz</abbr></code> zone, along with a polygonal representation of the geographical area corresponding to the zone.</li> <li>The <a href="http://lists.w3.org/Archives/Public/www-rdf-calendar/">www-rdf-calendar</a> list discusses <a href="http://www.w3.org/RDF/"><abbr title="Resource Description Framework">RDF</abbr></a>-based calendar and group scheduling systems, and has a <a href="http://www.w3.org/2002/12/cal/#tzd">workspace on time zone data</a> converted from <code><abbr>tz</abbr></code>.</li> </ul> <h2>Other <code><abbr>tz</abbr></code> compilers</h2> <ul> <li><a href="http://sourceforge.net/projects/vzic/">Vzic</a> is a <a href="http://en.wikipedia.org/wiki/C_%28programming_language%29">C</a> program that compiles <code><abbr>tz</abbr></code> source into iCalendar-compatible VTIMEZONE files. Vzic is freely available under the <a href="http://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr> General Public License (<abbr title="General Public License">GPL</abbr>)</a>.</li> <li><a href="http://sourceforge.net/projects/tzical">tziCal – tz database conversion utility</a> is like Vzic, except for the <a href="http://msdn.microsoft.com/netframework">.NET framework</a> and with a <abbr>BSD</abbr>-style license.</li> <li><a href="http://search.cpan.org/dist/DateTime-TimeZone/">DateTime::TimeZone</a> contains a script <code>parse_olson</code> that compiles <code><abbr>tz</abbr></code> source into <a href="http://www.perl.org">Perl</a> modules. It is part of the Perl <a href="http://datetime.perl.org">DateTime Project</a>, which is freely available under both the <abbr>GPL</abbr> and the Perl Artistic License. DateTime::TimeZone also contains a script <code>tests_from_zdump</code> that generates test cases for each clock transition in the <code><abbr>tz</abbr></code> database.</li> <li><a href="http://icu-project.org">International Components for Unicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a href="http://en.wikipedia.org/wiki/Java_%28programming_language%29">Java</a> libraries for internationalization that has a compiler from <code><abbr>tz</abbr></code> source and from <abbr title="Common Locale Data Repository">CLDR</abbr> data (mentioned below) into an <abbr>ICU</abbr>-specific format. <abbr>ICU</abbr> is freely available under a <abbr>BSD</abbr>-style license.</li> <li><a href="http://www.joda.org/joda-time/">Joda-Time – Java date and time <abbr title="Application Program Interface">API</abbr></a> contains a class <code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles <code><abbr>tz</abbr></code> source into a Joda-specific binary format. Joda Time is freely available under a <abbr>BSD</abbr>-style license.</li> <li><a href="http://nodatime.org">Noda Time – Date and time API for .NET</a> and <a href="http://www.babiej.demon.nl/Tz4Net/main.htm">TZ4Net</a> are similar to Joda Time, but for the .NET framework instead of Java. They are freely available under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License</a> and a <abbr>BSD</abbr>-style license, respectively.</li> <li><a href="http://en.wikipedia.org/wiki/JavaScript">JavaScript</a>-based compilers and libraries include: <ul> <li><a href="http://momentjs.com/timezone/">Moment Timezone</a> is a plugin for the <a href="http://momentjs.com">Moment.js</a> date manipulation library. It is freely available under the <abbr title="Massachusetts Institute of Technology">MIT</abbr> license.</li> <li><a href="https://github.com/mde/timezone-js">TimezoneJS.Date</a>'s <abbr>API</abbr> is upward compatible with standard JavaScript Dates. It is freely available under the Apache License.</li> <li><a href="https://github.com/sproutsocial/walltime-js">Walltime-js</a> translates <abbr>UT</abbr> to local time. It is freely available under the <abbr>MIT</abbr> license.</li> </ul> <li><a href="http://pytz.sourceforge.net">pytz – World Timezone Definitions for Python</a> compiles <code><abbr>tz</abbr></code> source into <a href="https://www.python.org">Python</a>. It is freely available under a <abbr>BSD</abbr>-style license.</li> <li><a href="http://tzinfo.github.io">TZInfo – Ruby Timezone Library</a> compiles <code><abbr>tz</abbr></code> source into <a href="http://www.ruby-lang.org/en/">Ruby</a>. It is freely available under the <abbr>MIT</abbr> license.</li> <li>The <a href="http://www.squeaksource.com/Chronos/">Chronos Date/Time Library</a> is a <a href="http://en.wikipedia.org/wiki/Smalltalk">Smalltalk</a> class library that compiles <code><abbr>tz</abbr></code> source into a time zone repository whose format is either proprietary or an <abbr>XML</abbr>-encoded representation.</li> <li><a href="http://tcl.tk">Tcl</a> contains a developer-oriented parser that compiles <code><abbr>tz</abbr></code> source into text files, along with a runtime that can read those files. Tcl is freely available under a <abbr>BSD</abbr>-style license.</li> </ul> <h2>Other <code><abbr>tz</abbr></code> binary file readers</h2> <ul> <li>The <a href="http://www.gnu.org/software/libc/"><abbr>GNU</abbr> C Library</a> has an independent, thread-safe implementation of a <code><abbr>tz</abbr></code> binary file reader. This library is freely available under the <a href="http://www.gnu.org/copyleft/lesser.html"> <abbr>GNU</abbr> Lesser General Public License (<abbr title="Lesser General Public License">LGPL</abbr>)</a>, and is widely used in <abbr>GNU</abbr>/Linux systems.</li> <li><a href="http://www.gnome.org">GNOME</a>'s Glib has a <code><abbr>tz</abbr></code> binary file reader written in C that creates a <code>GTimeZone</code> object representing sets of <abbr>UT</abbr> offsets. It is freely available under the <abbr>LGPL</abbr>.</li> <li><a href="http://bmsi.com/java/#TZ">ZoneInfo.java</a> is a <code><abbr>tz</abbr></code> binary file reader written in Java. It is freely available under the <abbr>LGPL</abbr>.</li> <li><a href="https://github.com/bigeasy/timezone">Timezone</a> is a JavaScript library that supports date arithmetic that is time zone aware. It is freely available under the <abbr>MIT</abbr> license.</li> <li>Tcl, mentioned above, also contains a <code><abbr>tz</abbr></code> binary file reader.</li> <li><a href="http://search.cpan.org/perldoc?DateTime::TimeZone::Tzfile"> DateTime::TimeZone::Tzfile</a> is a <code><abbr>tz</abbr></code> binary file reader written in Perl. It is freely available under the same terms as Perl (dual <abbr>GPL</abbr> and Artistic license).</li> <li>The public-domain <a href="https://github.com/dbaron/tz.js">tz.js</a> library contains a Python tool that converts <code><abbr>tz</abbr></code> binary data into <abbr>JSON</abbr>-format data suitable for use in its JavaScript library for time zone conversion. Dates before 1970 are not supported.</li> <li>The <a href="http://hackage.haskell.org/package/timezone-olson">timezone-olson</a> package contains <a href="http://haskell.org">Haskell</a> code that parses and uses <code><abbr>tz</abbr></code> binary data. It is freely available under a BSD-style license.</li> </ul> <h2>Other <code><abbr>tz</abbr></code>-based time zone software</h2> <ul> <li><a href="https://foxclocks.org">FoxClocks</a> is an extension for <a href="http://google.com/chrome/">Google Chrome</a> and for <a href="https://developer.mozilla.org/en-US/docs/Mozilla/Tech/Toolkit_API">Mozilla Toolkit</a> applications like <a href="https://www.mozilla.org/en-US/firefox/new/">Firefox</a> and <a href="https://www.mozilla.org/en-US/thunderbird/">Thunderbird</a>. It displays multiple clocks in the application window, and has a mapping interface to <a href="http://www.google.com/earth/">Google Earth</a>. It is freely available under the <abbr>GPL</abbr>.</li> <li><a href="http://golang.org">Go programming language</a> implementations contain a copy of a 32-bit subset of a recent <code><abbr>tz</abbr></code> database in a Go-specific format.</li> <li><a href="http://users.skynet.be/Peter.Verthez/projects/intclock/">International clock (intclock)</a> is a clock that displays multiple time zones on <abbr>GNU</abbr>/Linux and similar systems. It is freely available under the <abbr>GPL</abbr>.</li> <li>Microsoft Windows 8.1 and later has <code><abbr>tz</abbr></code> data and <abbr>CLDR</abbr> data (mentioned below) used by <a href="http://en.wikipedia.org/wiki/Windows_Runtime">Windows Runtime</a> classes such as <a href="http://msdn.microsoft.com/en-us/library/windows/apps/windows.globalization.datetimeformatting.datetimeformatter.aspx"><code>DateTimeFormatter</code></a>. <a href="http://blogs.msdn.com/b/bclteam/archive/2007/06/07/exploring-windows-time-zones-with-system-timezoneinfo-josh-free.aspx">Exploring Windows Time Zones with <code>System.TimeZoneInfo</code></a> describes the older, proprietary method of Microsoft Windows 2000 and later, which stores time zone data in the <a href="http://en.wikipedia.org/wiki/Windows_Registry">Windows Registry</a>. The <a href="http://www.unicode.org/cldr/charts/latest/supplemental/zone_tzid.html">Zone → Tzid table</a> or <a href="http://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml"><abbr>XML</abbr> file</a> of the <abbr>CLDR</abbr> data maps proprietary zone IDs to <code><abbr>tz</abbr></code> names. <li><a href="https://www.oracle.com/java/index.html">Oracle Java</a> contains a copy of a subset of a recent <code><abbr>tz</abbr></code> database in a Java-specific format.</li> <li><a href="https://kimmo.suominen.com/sw/timezone/">Time Zone</a> is a <a href="https://wordpress.org">WordPress</a> plugin. It is freely available under a <abbr>BSD</abbr>-style license.</li> <li><a href="http://www.relativedata.com/time-zone-master">Time Zone Master</a> is a Microsoft Windows clock program that can automatically download, compile and use the <code>tzdata<var>D</var>.tar.gz</code> files as they are released. The Basic version is free.</li> <li><a href="http://veladg.com/velaterra.html">VelaTerra</a> is an <abbr>OS X</abbr> program. Its developers <a href="http://veladg.com/tzoffer.html">offer free licenses</a> to <code><abbr>tz</abbr></code> contributors.</li> </ul> <h2>Other time zone databases</h2> <ul> <li><a href="http://www.astro.com/cgi/aq.cgi">Atlas Query</a> is Astrodienst's Web version of Shanks and Pottenger's time zone history atlases published in both <a href="http://astrocom.com/astrology-products/software/acs-atlas-software">computer</a> and book form (<a href="http://www.astrocom.com/astrology/books/american-atlas">one volume for the <abbr>US</abbr></a>, and <a href="http://www.astrocom.com/astrology/books/international-atlas">one for other locations</a>) by <a href="http://astrocom.com">Astro Computing Services</a>. These atlases are extensive but unreliable, as Shanks appears to have guessed many <abbr>UT</abbr> offsets and transitions. The atlases cite no sources and do not indicate which entries are guesswork.</li> <li><a href="http://en.wikipedia.org/wiki/HP-UX">HP-UX</a> has a database in its own <code>tztab</code>(4) format.</li> <li>Microsoft Windows has proprietary data mentioned above.</li> <li><a href="http://worldtimeserver.com">World Time Server</a> is another time zone database.</li> <li><a href="http://tycho.usno.navy.mil/tzones.html">World Time Zones</a> contains data from the Time Service Department of the <abbr>US</abbr> Naval Observatory.</li> <li>The <a href="http://www.iata.org/publications/Pages/ssim.aspx">Standard Schedules Information Manual</a> of the International Air Transport Association gives current time zone rules for airports served by commercial aviation.</li> </ul> <h2>Maps</h2> <ul> <li>The <a href="https://www.cia.gov/index.html">United States Central Intelligence Agency (<abbr title="Central Intelligence Agency">CIA</abbr>)</a> publishes a <a href="https://www.cia.gov/library/publications/the-world-factbook/graphics/ref_maps/physical/pdf/standard_time_zones_of_the_world.pdf">time zone map</a>; the <a href="http://www.lib.utexas.edu/maps/world.html">Perry–Castañeda Library Map Collection</a> 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.</li> <li><a href="http://worldtimezone.com">Current time around the world and standard time zones map of the world</a> has several fancy time zone maps; it covers Russia particularly well. The maps' pictorial quality is not quite as good as the <abbr>CIA</abbr>'s but the maps are more up to date.</li> <li><a href="http://poisson.phc.unipi.it/~maggiolo/index.php/2014/01/how-much-is-time-wrong-around-the-world/">How much is time wrong around the world?</a> 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.</li> </ul> <h2>Time zone boundaries</h2> <ul> <li><a href="http://efele.net/maps/tz/"><abbr>TZ</abbr> timezones maps</a> contains <a href="http://en.wikipedia.org/wiki/Shapefile">shapefiles</a> of sets of <code><abbr>tz</abbr></code> regions.</li> <li>The <a href="https://github.com/bradfitz/latlong">latlong package</a> maps geographical coordinates to a <code><abbr>tz</abbr></code> region. It is written in Go and is freely available under the Apache License.</li> <li><a href="http://derickrethans.nl/what-time-is-it.html">What Time is It Here?</a> applies <a href="http://www.mongodb.org">MongoDB</a> geospatial query operators to shapefiles' data.</li> <li><a href="http://statoids.com/statoids.html">Administrative Divisions of Countries ("Statoids")</a> contains lists of political subdivision data related to time zones.</li> <li><a href="http://home.kpn.nl/vanadovv/time/Multizones.html">Time zone boundaries for multizone countries</a> summarizes legal boundaries between time zones within countries.</li> <li>Manifold.net's <a href="http://manifold.net/info/freestuff.shtml">Free Stuff for Manifold System Users</a> includes a Manifold-format map of world time zone boundaries distributed under the <abbr>GPL</abbr>.</li> <li>The GeoCommunity lists several commercial sources for <a href="http://spatialnews.geocomm.com/features/timezones/">International Time Zones and Time Zone Data</a>.</li> <li>A ship within the <a href="http://en.wikipedia.org/wiki/Territorial_waters">territorial waters</a> of any nation uses that nation's time. In international waters, time zone boundaries are meridians 15° apart, except that <abbr>UTC</abbr>−12 and <abbr>UTC</abbr>+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.</li> </ul> <h2>Civil time concepts and history</h2> <ul> <li><a href="http://www.nist.gov/pml/general/time/index.cfm">A Walk through Time</a> surveys the evolution of timekeeping.</li> <li><a href="http://www.webexhibits.org/daylightsaving/">About Daylight Saving Time – History, rationale, laws & dates</a> is an overall history of <abbr>DST</abbr>.</li> <li><a href="http://www.w3.org/TR/timezone/">Working with Time Zones</a> contains guidelines and best practices for software applications that deal with civil time.</li> <li><a href="http://energy.ca.gov/daylightsaving.html">Saving Time, Saving Energy</a> discusses a primary justification for <abbr>DST</abbr>.</li> <li><a href="http://seizethedaylight.com/dst/">A Brief History of Daylight Saving Time</a> summarizes some of the contentious history of <abbr>DST</abbr>.</li> <li><a href="http://toi.inrim.it/uk/toi.html">The Time of Internet</a> describes time zones and daylight saving time, with diagrams. The time zone map is out of date, however.</li> <li><a href="http://www.staff.science.uu.nl/~gent0113/idl/idl.htm">A History of the International Date Line</a> tells the story of the most important time zone boundary.</li> <li><a href="http://statoids.com/tconcept.html">Basic Time Zone Concepts</a> discusses terminological issues behind time zones.</li> </ul> <h2>National histories of legal time</h2> <dl> <dt>Australia</dt> <dd>The Parliamentary Library has commissioned a <a href="http://www.aph.gov.au/binaries/library/pubs/rp/2009-10/10rp10.pdf">research paper on daylight saving time in Australia</a>. The Bureau of Meteorology publishes a list of <a href="http://www.bom.gov.au/climate/averages/tables/dst_times.shtml">Implementation Dates of Daylight Savings Time within Australia</a>.</dd> <dt>Belgium</dt> <dd>The Royal Observatory of Belgium maintains a table of <a href="http://www.astro.oma.be/GENERAL/INFO/nli001a.html" hreflang="nl">time in Belgium (in Dutch)</a>.</dd> <dt>Brazil</dt> <dd>The Time Service Department of the National Observatory records <a href="http://pcdsh01.on.br/DecHV.html" hreflang="pt-BR">Brazil's daylight saving time decrees (in Portuguese)</a>.</dd> <dt>Canada</dt> <dd>National Research Council Canada publishes current and some older information about <a href="http://www.nrc-cnrc.gc.ca/eng/services/time/time_zones.html">time zones & daylight saving time</a>.</dd> <dt>Chile</dt> <dd>The Hydrographic and Oceanographic Service of the Chilean Navy publishes a <a href="http://www.horaoficial.cl/historia_hora.html" hreflang="es">history of Chile's official time (in Spanish)</a>.</dd> <dt>Germany</dt> <dd>The National Institute for Science and Technology maintains the <a href="http://www.ptb.de/cms/en/fachabteilungen/abt4/fb-44/ag-441/realisation-of-legal-time-in-germany.html">Realisation of Legal Time in Germany</a>.</dd> <dt>Israel</dt> <dd>The Interior Ministry periodically issues <a href="ftp://ftp.cs.huji.ac.il/pub/tz/announcements" hreflang="he">announcements (in Hebrew)</a>.</dd> <dt>Mexico</dt> <dd>The Investigation and Analysis Service of the Mexican Library of Congress has published a <a href="http://www.diputados.gob.mx/bibliot/publica/inveyana/polisoc/horver/index.htm" hreflang="es">history of Mexican local time (in Spanish)</a>.</dd> <dt>Malaysia</dt> <dd>See Singapore below.</dd> <dt>Netherlands</dt> <dd><a href="http://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm" hreflang="nl">Legal time in the Netherlands (in Dutch)</a> covers the history of local time in the Netherlands from ancient times.</dd> <dt>New Zealand</dt> <dd>The Department of Internal Affairs maintains a brief <a href="http://www.dia.govt.nz/Daylight-Saving-History">History of Daylight Saving</a>. The privately-maintained <a href="http://astrologyschool.com/nztime.html">History of New Zealand time</a> has more details.</dd> <dt>Singapore</dt> <dd><a href="http://www.math.nus.edu.sg/aslaksen/teaching/timezone.html">Why is Singapore in the "Wrong" Time Zone?</a> details the history of legal time in Singapore and Malaysia.</dd> <dt>United Kingdom</dt> <dd><a href="http://www.polyomino.org.uk/british-time/">History of legal time in Britain</a> discusses in detail the country with perhaps the best-documented history of clock adjustments. The National Physical Laboratory also maintains an <a href="http://www.npl.co.uk/educate-explore/what-is-time/archive-of-summer-time-dates-1916-2006">Archive of Summer time dates</a>.</dd> </dl> <h2>Precision timekeeping</h2> <ul> <li><a href="http://literature.agilent.com/litweb/pdf/5965-7984E.pdf">The Science of Timekeeping</a> is a thorough introduction to the theory and practice of precision timekeeping.</li> <li><a href="http://www.ntp.org"><abbr title="Network Time Protocol">NTP</abbr>: The Network Time Protocol</a> discusses how to synchronize clocks of Internet hosts.</li> <li>The <a href="http://www.nist.gov/el/isd/ieee/ieee1588.cfm">Precision Time Protocol</a> (<abbr title="Institute of Electrical and Electronics Engineers">IEEE</abbr> 1588) can achieve submicrosecond clock accuracy on a local area network.</li> <li><a href="http://tools.ietf.org/html/rfc4833">Timezone Options for <abbr title="Dynamic Host Configuration Protocol">DHCP</abbr></a> (Internet <abbr>RFC</abbr> 4833) specifies a <a href="http://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol"><abbr>DHCP</abbr></a> option for a server to configure a client's time zone and daylight saving settings automatically.</li> <li><a href="http://gauss.gge.unb.ca/GMT.UT.and.the.RGO.html">A Few Facts Concerning <abbr>GMT</abbr>, <abbr>UT</abbr>, and the <abbr title="Royal Greenwich Observatory">RGO</abbr></a> answers questions like "What is the difference between <abbr>GMT</abbr> and <abbr>UTC</abbr>?"</li> <li><a href="http://www.cv.nrao.edu/~rfisher/Ephemerides/times.html">Astronomical Times</a> explains more abstruse astronomical time scales like <abbr title="Terrestrial Dynamic Time">TDT</abbr>, <abbr title="Geocentric Coordinate Time">TCG</abbr>, and <abbr title="Barycentric Dynamic Time">TDB</abbr>. <a href="http://www.ucolick.org/~sla/leapsecs/timescales.html">Time Scales</a> goes into more detail, particularly for historical variants.</li> <li>The <a href="http://iau.org"><abbr title="International Astronomical Union">IAU</abbr></a>'s <a href="http://www.iausofa.org"><abbr title="Standards Of Fundamental Astronomy">SOFA</abbr></a> collection contains C and <a href="http://en.wikipedia.org/wiki/Fortran">Fortran</a> code for converting among time scales like <abbr title="International Atomic Time">TAI</abbr>, <abbr>TDB</abbr>, <abbr>TDT</abbr> and <abbr>UTC</abbr>.</li> <li><a href="http://www2.jpl.nasa.gov/basics/bsf2-3.php">Basics of Space Flight – Reference Systems – Time Conventions</a> briefly explains interplanetary space flight timekeeping.</li> <li><a href="http://www.giss.nasa.gov/tools/mars24/help/notes.html">Technical Notes on Mars Solar Time as Adopted by the Mars24 Sunclock</a> briefly describes Mars Coordinated Time (<abbr title="Mars Coordinated Time">MTC</abbr>) and the diverse local time scales used by each landed mission on Mars.</li> <li><a href="http://leapsecond.com">LeapSecond.com</a> 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.</li> <li><a href="http://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html"><abbr title="International Earth Rotation and Reference Systems Service">IERS</abbr> Bulletins</a> contains official publications of the International Earth Rotation and Reference Systems Service, which decides when leap seconds occur.</li> <li>The <a href="https://pairlist6.pair.net/mailman/listinfo/leapsecs">Leap Second Discussion List</a> covers <a href="http://gauss.gge.unb.ca/papers.pdf/gpsworld.november99.pdf">McCarthy and Klepczynski's proposal to discontinue leap seconds</a>, discussed further in <a href="http://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The leap second: its history and possible future</a>. <a href="http://www.ucolick.org/~sla/leapsecs/"><abbr>UTC</abbr> might be redefined without Leap Seconds</a> gives pointers on this contentious issue.</li> </ul> <h2>Time notation</h2> <ul> <li>The <a href="http://cldr.unicode.org">Unicode Common Locale Data Repository (<abbr>CLDR</abbr>) Project</a> has localizations for time zone names, abbreviations, identifiers, and formats. For example, it contains French translations for "Eastern European Summer Time", "<abbr title="Eastern European Summer Time">EEST</abbr>", and "Bucharest". Its <a href="http://unicode.org/cldr/charts/by_type/index.html">by-type charts</a> show these values for many locales. Data values are available in both <abbr title="Locale Data Markup Language">LDML</abbr> (an <abbr>XML</abbr> format) and <abbr>JSON</abbr>. <li> <a href="http://www.cl.cam.ac.uk/~mgk25/iso-time.html">A summary of the international standard date and time notation</a> is a good summary of <a href="http://www.iso.org/iso/catalogue_detail?csnumber=40874"><abbr title="International Organization for Standardization">ISO</abbr> 8601:2004 – Data elements and interchange formats – Information interchange – Representation of dates and times</a>.</li> <li> <a href="http://www.w3.org/TR/xmlschema-2/#dateTime"><abbr>XML</abbr> Schema: Datatypes – dateTime</a> specifies a format inspired by <abbr>ISO</abbr> 8601 that is in common use in <abbr>XML</abbr> data.</li> <li> <a href="http://tools.ietf.org/html/rfc5322">Internet Message Format</a> (Internet <abbr>RFC</abbr> 5322) §3.3 specifies the time notation used in email and <a href="http://www.w3.org/Protocols/"><abbr>HTTP</abbr></a> headers.</li> <li> <a href="http://tools.ietf.org/html/rfc3339">Date and Time on the Internet: Timestamps</a> (Internet <abbr>RFC</abbr> 3339) specifies an <abbr>ISO</abbr> 8601 profile for use in new Internet protocols.</li> <li> <a href="http://www.hackcraft.net/web/datetime/">Date & Time Formats on the Web</a> surveys web- and Internet-oriented date and time formats.</li> <li> <a href="http://exit109.com/~ghealton/y2k/yrexamples.html">The Best of Dates, the Worst of Dates</a> covers many problems encountered by software developers when handling dates and time stamps.</li> <li>Alphabetic time zone abbreviations should not be used as unique identifiers for <abbr>UTC</abbr> offsets as they are ambiguous in practice. For example, in English-speaking North America "<abbr>CST</abbr>" denotes 6 hours behind <abbr>UTC</abbr>, but in China it denotes 8 hours ahead of <abbr>UTC</abbr>, and French-speaking North Americans prefer "<abbr title="Heure Normale du Centre">HNC</abbr>" to "<abbr>CST</abbr>". For <abbr>POSIX</abbr> the <code><abbr>tz</abbr></code> database contains English abbreviations for all time stamps but in many cases these are merely inventions of the database maintainers.</li> <li>Numeric time zone abbreviations typically count hours east of <abbr>UTC</abbr>, e.g., +09 for Japan and −10 for Hawaii. However, the <abbr>POSIX</abbr> <code><abbr>TZ</abbr></code> environment variable uses the opposite convention. For example, one might use <code><abbr>TZ</abbr>="<abbr title="Japan Standard Time">JST</abbr>-9"</code> and <code><abbr>TZ</abbr>="<abbr title="Hawaii Standard Time">HST</abbr>10"</code> for Japan and Hawaii, respectively. If the <code><abbr>tz</abbr></code> database is available, it is usually better to use settings like <code><abbr>TZ</abbr>="Asia/Tokyo"</code> and <code><abbr>TZ</abbr>="Pacific/Honolulu"</code> 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 <abbr>POSIX</abbr> <code><abbr>TZ</abbr></code> to a value like <code>"GMT-9"</code>, though, since this would falsely claim that local time is nine hours ahead of <abbr>UTC</abbr> and the time zone is called "<abbr>GMT</abbr>".</li> </ul> <h2>Related indexes</h2> <ul> <li><a href="http://www.dmoz.org/Reference/Time/">Open Directory – Reference: Time</a></li> <li><a href="https://dir.yahoo.com/science/measurements_and_units/time">Yahoo! Directory > Science > Measurements and Units > Time</a></li> </ul> <hr> <address> This web page is in the public domain, so clarified as of 2009-05-17 by Arthur David Olson. <br> Please send corrections to this web page to the <a href="mailto:tz@iana.org">time zone mailing list</a>. </address> </body> </html>