1<!DOCTYPE html 2 PUBLIC "-//W3C//DTD HTML 4.01//EN" 3 "http://www.w3.org/TR/html4/strict.dtd"> 4<html> 5<head> 6<title>Sources for Time Zone and Daylight Saving Time Data</title> 7<link rel="schema.DC" href="http://purl.org/DC/elements/1.1/"> 8<meta http-equiv="Content-type" content='text/html; charset="US-ASCII"'> 9<meta name="DC.Creator" content="Eggert, Paul"> 10<meta name="DC.Contributor" content="Olson, Arthur David"> 11<meta name="DC.Date" content="2007-12-26"> 12<meta name="DC.Description" 13 content="Sources of information about time zones and daylight saving time"> 14<meta name="DC.Identifier" content="http://www.twinsun.com/tz/tz-link.htm"> 15<meta name="Keywords" 16 content="database,daylight saving,DST,time zone,timezone,tz,zoneinfo"> 17</head> 18<body> 19<h1>Sources for Time Zone and Daylight Saving Time Data</h1> 20<address> 21@(#)tz-link.htm 8.32 22</address> 23<p> 24This file is in the public domain, so clarified as of 252009-05-17 by Arthur David Olson. 26</p> 27<p> 28Please send corrections to this web page to the 29<a href="mailto:tz@elsie.nci.nih.gov">time zone mailing list</a>.</p> 30<h2>The <code>tz</code> database</h2> 31<p> 32The <a href="http://en.wikipedia.org/wiki/Public_domain">public-domain</a> 33time zone database contains code and data 34that represent the history of local time 35for many representative locations around the globe. 36It is updated periodically to reflect changes made by political bodies 37to <a href="http://en.wikipedia.org/wiki/Time_zone">time zone</a> 38boundaries, <a 39href="http://en.wikipedia.org/wiki/Coordinated_Universal_Time"><abbr 40title="Coordinated Universal Time">UTC</abbr></a> offsets, and 41<a href="http://en.wikipedia.org/wiki/Daylight_saving">daylight-saving</a> 42rules. 43This database (often called <code>zoneinfo</code> or <a 44href="http://en.wikipedia.org/wiki/TZ_database"><code>tz</code></a>) 45is used by several implementations, 46including 47<a href="http://www.gnu.org/software/libc/">the 48<abbr title="GNU's Not Unix">GNU</abbr> 49C Library</a> used in 50<a href="http://www.linux.org/"><abbr>GNU</abbr>/Linux</a>, 51<a href="http://www.freebsd.org/">FreeBSD</a>, 52<a href="http://netbsd.org/">NetBSD</a>, 53<a href="http://openbsd.org/">OpenBSD</a>, 54<a href="http://cygwin.com/">Cygwin</a>, 55<a href="http://www.delorie.com/djgpp/"><abbr 56title="DJ's GNU Programming Platform">DJGPP</abbr></a>, 57<a href="http://ibm.com/aix">AIX</a>, 58<a href="http://www.apple.com/macosx/">Mac OS X</a>, 59<a href="http://h71000.www7.hp.com/">OpenVMS</a>, 60<a href="http://oracle.com/database">Oracle Database</a>, 61<a href="http://sun.com/software/solaris">Solaris</a>, 62<a href="http://h30097.www3.hp.com/">Tru64</a>, and 63<a href="http://sco.com/products/unixware">UnixWare</a>.</p> 64<p> 65Each location in the database represents a national region where all 66clocks keeping local time have agreed since 1970. 67Locations are identified by continent or ocean and then by the name of 68the location, which is typically the largest city within the region. 69For example, <code>America/New_York</code> 70represents most of the <abbr title="United States">US</abbr> eastern time zone; 71<code>America/Phoenix</code> represents most of Arizona, which 72uses mountain time without daylight saving time (<abbr 73title="daylight saving time">DST</abbr>); 74<code>America/Detroit</code> represents most of Michigan, which uses 75eastern time but with different <abbr>DST</abbr> rules in 1975; 76and other entries represent smaller regions like Starke County, 77Indiana, which switched from central to eastern time in 1991 78and switched back in 2006. 79To use the database on an extended <a 80href="http://en.wikipedia.org/wiki/POSIX"><abbr 81title="Portable Operating System Interface">POSIX</abbr></a> 82implementation set the <code>TZ</code> environment variable to 83the location's full name, e.g., <code>TZ="America/New_York"</code>.</p> 84<p> 85In the <code>tz</code> database's 86<a href="ftp://elsie.nci.nih.gov/pub"><abbr 87title="File Transfer Protocol">FTP</abbr> distribution</a> 88the code is in the file <code>tzcode<var>C</var>.tar.gz</code>, 89where <code><var>C</var></code> is the code's version; 90similarly, the data are in <code>tzdata<var>D</var>.tar.gz</code>, 91where <code><var>D</var></code> is the data's version. 92Each version is a four-digit year followed by lower-case letters 93(a through z, then za through zz, then zza through zzz, and so on). 94The following <a 95href="http://en.wikipedia.org/wiki/Unix_shell">shell</a> commands download 96these files to a <abbr>GNU</abbr>/Linux or similar host; 97see the downloaded 98<code>README</code> file for what to do next.</p> 99<pre style="margin-left: 2em"><code>mkdir tz 100cd tz 101<a href="http://www.gnu.org/software/wget/">wget</a> 'ftp://elsie.nci.nih.gov/pub/tz*.tar.gz' 102<a href="http://www.gnu.org/software/gzip/">gzip</a> -dc tzcode*.tar.gz | <a href="http://www.gnu.org/software/tar/">tar</a> -xf - 103gzip -dc tzdata*.tar.gz | tar -xf - 104</code></pre> 105<p> 106The code lets you compile the <code>tz</code> source files into 107machine-readable binary files, one for each location. It also lets 108you read a <code>tz</code> binary file and interpret time stamps for that 109location.</p> 110<p> 111The data are by no means authoritative. If you find errors, please 112send changes to the <a href="mailto:tz@elsie.nci.nih.gov">time zone 113mailing list</a>. You can also <a 114href="http://news.gmane.org/gmane.comp.time.tz">browse recent 115messages</a> sent to the mailing list, <a 116href="mailto:tz-request@elsie.nci.nih.gov">subscribe</a> to it, 117retrieve the <a 118href="ftp://elsie.nci.nih.gov/pub/tzarchive.gz">full archive of old 119messages</a> (in gzip compressed format), or retrieve <a 120href="ftp://munnari.oz.au/pub/oldtz">archived older versions of code 121and data</a>.</p> 122<p> 123The Web has several other sources for time zone and daylight saving time data. 124Here are some recent links that may be of interest. 125</p> 126<h2>Web pages using recent versions of the <code>tz</code> database</h2> 127<p> 128These are listed roughly in ascending order of complexity and fanciness. 129</p> 130<ul> 131<li> 132<a href="http://permatime.com"> 133Permatime</a> 134is a service for generating and viewing links that refer to a 135particular point in time and can be displayed in multiple timezones. 136It uses the ruby tzinfo gem. 137(From Tim Diggins, 2009-11-03.) 138</li> 139<li><a href="http://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a> 140lets you see the <code>TZ</code> values directly.</li> 141<li><a 142href="http://convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current 143Time in 1000 Places</a> uses descriptions of the values.</li> 144<li><a href="http://www.timezoneconverter.com/">Time Zone Converter</a> 145uses a pulldown menu.</li> 146<li><a href="http://home.tiscali.nl/~t876506/TZworld.html">Complete 147timezone information for all countries</a> displays tables of DST rules. 148<li><a href="http://timeanddate.com/worldclock/">The World Clock - 149Time Zones</a> lets you sort zone names and convert times.</li> 150<li><a href="http://daylight-savings-time.info/">Graphical Display of 151Time Zones and Daylight Saving Times</a> shows a graph of time 152difference versus time for any pair of locations.</li> 153<li>The <a href="http://worldtimeengine.com/">World Time Engine</a> 154also contains data about time zone boundaries; it supports queries via place 155names and shows location maps.</li> 156<li><a href="http://simpletimerclocks.mozdev.org/">Simple Timer + Clocks</a> 157is a Firefox add-on which uses a timezone data file generated from the 158tz data files.</li> 159</ul> 160<h2>Other time zone database formats</h2> 161<ul> 162<li>The <a href="ftp://ftp.rfc-editor.org/in-notes/rfc2445.txt"> 163Internet Calendaring and Scheduling Core Object Specification 164(iCalendar)</a>, Internet <abbr title="Request For 165Comments">RFC</abbr> 2445, published by the (now-concluded) <a 166href="http://ietf.org/html.charters/OLD/calsch-charter.html"><abbr 167title="Internet Engineering Task Force">IETF</abbr> 168Calendaring and Scheduling Working Group (<abbr 169title="Calendaring and Scheduling Working Group">calsch</abbr>)</a> 170covers time zone 171data; see its VTIMEZONE calendar component. 172The <a href="http://calconnect.org/">Calendaring and Scheduling 173Consortium</a> is promoting further work in this area. <a 174href="http://calconnect.org/publications/icalendartimezoneproblemsandrecommendationsv1.0.pdf">iCalendar 175TIMEZONE Problems and Recommendations</a> offers guidelines and 176recommendations for the use of VTIMEZONE and <code>tz</code>.</li> 177<li><a href="http://calconnect.org/dstlinks.shtml">Extended Daylight 178Saving Time Links, Advisories and Changes</a> lists vendor material on recent 179daylight saving time changes.</li> 180<li><a 181href="http://calconnect.org/publications/timezoneregistryandservicerecommendationsv1.0.pdf">Timezone 182Registry and Service Recommendations</a> discusses a 183strategy for defining and deploying a time zone 184registration process that would establish unique names for each 185version of each <code>tz</code> zone, along with a polygonal 186representation of the geographical area corresponding to the 187zone.</li> 188<li>The <a 189href="http://lists.w3.org/Archives/Public/www-rdf-calendar/">www-rdf-calendar</a> 190list discusses <a 191href="http://www.w3.org/RDF/"><abbr 192title="Resource Description Framework">RDF</abbr></a>-based calendar 193and group scheduling systems, and has a <a 194href="http://www.w3.org/2002/12/cal/#tzd">workspace on time zone 195data</a> converted from <code>tz</code>. An earlier <a 196href="http://www.w3.org/2000/01/foo">schema</a> was sketched out.</li> 197</ul> 198<h2>Other <code>tz</code> compilers</h2> 199<ul> 200<li><a href="http://www.dachaplin.dsl.pipex.com/vzic/">Vzic iCalendar 201Timezone Converter</a> describes a <a 202href="http://en.wikipedia.org/wiki/C_%28programming_language%29">C</a> 203program that compiles 204<code>tz</code> source into iCalendar-compatible VTIMEZONE files. 205Vzic is freely 206available under the <a 207href="http://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr> 208General Public License (<abbr 209title="General Public License">GPL</abbr>)</a>.</li> 210<li><a href="http://sourceforge.net/projects/tzical">tziCal - tz 211database conversion utility</a> is like Vzic, except for the <a 212href="http://msdn.microsoft.com/netframework">.NET framework</a>.</li> 213<li><a 214href="http://search.cpan.org/dist/DateTime-TimeZone/">DateTime::TimeZone</a> 215contains a script <code>parse_olson</code> that compiles 216<code>tz</code> source into <a href="http://www.perl.org/">Perl</a> 217modules. It is part of the Perl <a 218href="http://datetime.perl.org/">DateTime Project</a>, which is freely 219available under both the <abbr>GPL</abbr> and the Perl Artistic 220License. DateTime::TimeZone also contains a script 221<code>tests_from_zdump</code> that generates test cases for each clock 222transition in the <code>tz</code> database.</li> 223<li><a href="http://icu-project.org/">International Components for 224Unicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a 225href="http://en.wikipedia.org/wiki/Java_%28programming_language%29">Java</a> 226libraries for internationalization that 227has a compiler from <code>tz</code> source 228into an <abbr>ICU</abbr>-specific format. 229<abbr>ICU</abbr> is freely available under a 230<abbr title="Berkeley Software Distribution">BSD</abbr>-style license.</li> 231<li><a href="http://joda-time.sourceforge.net/">Joda Time - Java date 232and time <abbr title="Application Program Interface">API</abbr></a> 233contains a class 234<code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles 235<code>tz</code> source into a Joda-specific binary format. Joda Time 236is freely available under a <abbr>BSD</abbr>-style license.</li> 237<li><a href="http://pytz.sourceforge.net">PyTZ - Python Time 238Zone Library</a> compiles <code>tz</code> source into 239<a href="http://python.org/">Python</a>. 240It is freely available under a <abbr>BSD</abbr>-style license.</li> 241<li><a href="http://tzinfo.rubyforge.org/">TZInfo - Ruby Timezone Library</a> 242compiles <code>tz</code> source into 243<a href="http://ruby-lang.org">Ruby</a>. 244It is freely available under the <abbr 245title="Massachusetts Institute of Technology">MIT</abbr> license.</li> 246<li>The <a href="http://chronos-st.org/">Chronos Date/Time 247Library</a> is a <a href="http://smalltalk.org">Smalltalk</a> class 248library that compiles <code>tz</code> source into a <a 249href="http://date-time-zone.com/">time zone repository</a> whose format 250is either proprietary or an <a href="http://www.w3.org/XML/"><abbr 251title="Extensible Markup Language">XML</abbr></a>-encoded 252representation.</li> 253<li>Starting with version 8.5, <a href="http://tcl.tk/">Tcl</a> 254contains a developer-oriented parser that compiles <samp>tz</samp> 255source into text files, along with a runtime that can read those 256files. Tcl is freely available under a <abbr>BSD</abbr>-style 257license.</li> 258</ul> 259<h2>Other <code>tz</code> binary file readers</h2> 260<ul> 261<li>The <a 262href="http://www.gnu.org/software/libc/"><abbr>GNU</abbr> C 263Library</a> 264has an independent, thread-safe implementation of 265a <code>tz</code> binary file reader. 266This library is freely available under the 267<a href="http://www.gnu.org/copyleft/lesser.html"> 268<abbr>GNU</abbr> Lesser General Public License 269(<abbr title="Lesser General Public License">LGPL</abbr>)</a>, 270and is widely used in <abbr>GNU</abbr>/Linux systems.</li> 271<li><a href="http://bmsi.com/java/#TZ">ZoneInfo.java</a> 272is a <code>tz</code> binary file reader written in Java. 273It is freely available under the <abbr>LGPL</abbr>.</li> 274<li>Tcl, mentioned above, also contains a 275<code>tz</code> binary file reader.</li> 276</ul> 277<h2>Other <code>tz</code>-based time zone software</h2> 278<ul> 279<li><a href="http://stemhaus.com/firefox/foxclocks/">FoxClocks</a> 280is an extension for <a 281href="http://developer.mozilla.org/en/docs/Toolkit_API">Mozilla 282Toolkit</a> applications like <a 283href="http://mozilla.com/firefox">Firefox</a>, <a 284href="http://mozilla.com/thunderbird">Thunderbird</a>, and 285<a 286href="http://www.mozilla.org/projects/calendar/sunbird/">Sunbird</a>. 287It displays multiple clocks in the application window, and has a mapping 288interface to <a href="http://earth.google.com/">Google Earth</a>. 289It is freely available under the <abbr>GPL</abbr>.</li> 290<li><a 291href="http://users.skynet.be/Peter.Verthez/projects/intclock/">International 292clock (intclock)</a> is a multi-timezone clock for 293<abbr>GNU</abbr>/Linux and similar systems. It is freely available 294under the <abbr>GPL</abbr>.</li> 295<li><a href="http://codeplex.com/publicdomain">PublicDomain</a> 296has a copy of a recent <code>tz</code> database, accessed via a <a 297href="http://en.wikipedia.org/wiki/C_Sharp">C#</a> library. As its 298name suggests, it is in the public domain. Only current time stamps 299are well supported; historical data are compiled into the runtime but 300are not easily accessible.</li> 301<li><a href="http://java.sun.com/">Sun Java</a> releases since 1.4 302contain a copy of a subset of a recent <code>tz</code> database in a 303Java-specific format.</li> 304<li><a href="http://kimmo.suominen.com/sw/timezone/">Time Zone</a> is 305a <a href="http://wordpress.org/">WordPress</a> plugin. It is freely 306available under a <abbr>BSD</abbr>-style license.</li> 307<li><a 308href="http://veladg.com/velaterra.html">VelaTerra</a> is 309a Mac OS X program. Its developers 310<a href="http://veladg.com/tzoffer.html">offer free 311licenses</a> to <code>tz</code> contributors.</li> 312<li><a 313href="http://worldtimeexplorer.com/">World Time Explorer</a> is a 314Microsoft Windows program.</li> 315<li> 316<a href="http://www.toriasoft.com"> 317WorldClock for Windows and Windows Mobile</a> 318lets users "see the time in up to 25 locations in the world at once." 319(From Hans Nieuwenhuis, 2009-11-02.) 320</li> 321<li> 322<a href="http://www.relativedata.com/time-zone-master"> 323Time Zone Master Basic 324</a> "allows people to display multiple desktop clocks, and to 325research current and historical time information, as well as times of 326astronomical events (sunrise/transit/set, moonrise/transit/set, phases, 327season starts) for user-selected dates in the past and future. It can 328automatically download, compile and use the tzdata**.gz database files 329as they are released to keep the data up to date. The software is 330free." (Davie Patte) 331</li> 332</ul> 333<h2>Other time zone databases</h2> 334<ul> 335<li><a href="http://www.astro.com/cgi/aq.cgi">Atlas Query</a> 336is Astrodienst's Web version of Shanks's 337excellent time zone history atlases published in both <a 338href="http://astrocom.com/products/software.php?software_id=ibmwboth">computer</a> 339and book form (<a 340href="http://astrocom.com/products/book.php?book_id=b110x">one volume 341for the USA</a>, and <a 342href="http://astrocom.com/products/book.php?book_id=b112x">one for 343other locations</a>) by <a 344href="http://astrocom.com/">Astro Communications Services</a>.</li> 345<li><a href="http://worldtime.com/">WORLDTIME: interactive atlas, 346time info, public holidays</a> 347contains information on local time, sunrise and sunset, 348and public holidays in several hundred cities around the world.</li> 349<li><a href="http://worldtimeserver.com/">World Time Server</a> 350is another time zone database.</li> 351<li><a href="http://tycho.usno.navy.mil/tzones.html">World Time Zones</a> 352contains data from the Time Service Department of the 353<abbr>US</abbr> Naval Observatory, used as the source 354for the <code>usno*</code> files in the <code>tz</code> distribution.</li> 355<li>The <a href="http://iata.org/ps/publications/SSIM.htm">Standard 356Schedules Information Manual</a> of the 357<a href="http://iata.org/index.htm">International Air Transport 358Association</a> 359gives current time zone rules for airports served by commercial aviation.</li> 360<li>Some Microsoft Windows versions contain time zone information in 361an undocumented format, with IDs that can be mapped to <code>TZ</code> 362values using the <a 363href="http://unicode.org/cldr/data/diff/supplemental/windows_tzid.html">Windows 364→ Tzid table</a> maintained by the <abbr 365title="Common Locale Data Repository">CLDR</abbr> data mentioned 366below.</li> 367<li> 368<a href="http://code.google.com/p/tzdata/"> 369http://code.google.com/p/tzdata/ 370</a> 371provides programming-language-specific representations of timezone 372data. Currently this includes XML, PHP, Ruby, Javascript, JSON and CSV 373formatted data. The repository is updated as soon as the FTP 374distribution is updated. All data can be downloaded as a zip and/or it 375can be obtained/synced via anonymous SVN. Data is made available under 376the MIT license. (From Rich Tibbett.) 377</li> 378</ul> 379<h2>Maps</h2> 380<ul> 381<li>The <a href="https://www.cia.gov/">United States Central 382Intelligence Agency (<abbr 383title="Central Intelligence Agency">CIA</abbr>)</a> publishes a <a 384href="https://www.cia.gov/library/publications/the-world-factbook/reference_maps/pdf/time_zones.pdf">time 385zone map</a>; the 386<a 387href="http://www.lib.utexas.edu/maps/world.html">Perry-Castañeda 388Library Map Collection</a> 389of the University of Texas at Austin has copies of 390recent editions. 391The pictorial quality is good, 392but the maps do not indicate summer time, 393and parts of the data are a few years out of date.</li> 394<li><a href="http://worldtimezone.com/">Current time around the world 395and standard time zones map of the world</a> 396has several fancy time zone maps; it covers Russia particularly well. 397The maps' pictorial quality is not quite as good as the 398<abbr>CIA</abbr>'s 399but the maps are more up to date.</li> 400</ul> 401<h2>Time zone boundaries</h2> 402<ul> 403<li><a href="http://efele.net/maps/tz/">TZ timezone maps</a> contains a <a 404href="http://en.wikipedia.org/wiki/Shapefile">shapefile</a> of the 405<code>tz</code> regions in the world.</li> 406<li><a href="http://statoids.com/statoids.html">Administrative Divisions 407of Countries ("Statoids")</a> contains detailed lists of 408<code>tz</code>-related zone subdivision data.</li> 409<li><a href="http://home.tiscali.nl/~t876506/Multizones.html">Time 410zone boundaries for multizone countries</a> summarizes legal 411boundaries between time zones within countries.</li> 412<li>Manifold.net's <a 413href="http://www.manifold.net/download/freemaps.html">Free Maps and 414<abbr title="Geographic Information Systems">GIS</abbr> 415Data</a> includes a Manifold-format map of 416world time zone boundaries distributed under the 417<abbr>GPL</abbr>.</li> 418<li>The <abbr>US</abbr> Geological Survey's National Atlas of 419the United States 420publishes the <a href="http://nationalatlas.gov/mld/timeznp.html">Time 421Zones of the United States</a> in the public domain.</li> 422<li>The GeoCommunity lists several commercial sources for <a 423href="http://spatialnews.geocomm.com/features/timezones/">International 424Time Zones and Time Zone Data</a>.</li> 425<li>A ship within the <a 426href="http://en.wikipedia.org/wiki/Territorial_waters">territorial 427waters</a> of any nation uses that nation's time. In international 428waters, time zone boundaries are meridians 15° apart, except that 429UTC−12 and UTC+12 are each 7.5° wide and are separated by 430the 180° meridian (not by the International Date Line, which is 431for land and territorial waters only). A captain can change ship's 432clocks any time after entering a new time zone; midnight changes are 433common.</li> 434</ul> 435<h2>Civil time concepts and history</h2> 436<ul> 437<li><a href="http://physics.nist.gov/GenInt/Time/time.html">A 438Walk through Time</a> 439surveys the evolution of timekeeping.</li> 440<li><a href="http://webexhibits.org/daylightsaving/">About Daylight 441Saving Time - History, rationale, laws & dates</a> 442is an overall history of <abbr>DST</abbr>.</li> 443<li><a href="http://energy.ca.gov/daylightsaving.html">Saving Time, 444Saving Energy</a> discusses a primary justification for <abbr>DST</abbr>.</li> 445<li><a href="http://seizethedaylight.com/dst/">Who Knew? A Brief 446History of Daylight Saving Time</a> summarizes some of the contentious 447history of <abbr>DST</abbr>.</li> 448<li><a href="http://toi.iriti.cnr.it/">The 449Time of Internet</a> 450describes time zones and daylight saving time, 451with diagrams. 452The time zone map is out of date, however.</li> 453<li><a href="http://www.phys.uu.nl/~vgent/idl/idl.htm">A History of 454the International Date Line</a> tells the story of the most important 455time zone boundary.</li> 456<li><a href="http://statoids.com/tconcept.html">Basic Time 457Zone Concepts</a> discusses terminological issues behind time zones.</li> 458</ul> 459<h2>National histories of legal time</h2> 460<dl> 461<dt>Australia</dt> 462<dd>The Parliamentary Library has commissioned <a 463href="http://www.aph.gov.au/LIBRARY/Pubs/rn/2006-07/07rn13.pdf">research 464note on daylight saving time in Australia</a>. 465The Bureau of Meteorology publishes a list of 466<a href="http://www.bom.gov.au/climate/averages/tables/dst_times.shtml">Implementation Dates of Daylight Savings Time within Australia</a>.</dd> 467<dt>Belgium</dt> 468<dd>The Royal Observatory of Belgium maintains a table of <a 469href="http://www.astro.oma.be/GENERAL/INFO/nli001a.html" 470hreflang="nl">time in Belgium (in Dutch)</a>.</dd> 471<dt>Brazil</dt> 472<dd>The Time Service Department of the National Observatory 473records <a href="http://pcdsh01.on.br/DecHV.html" 474hreflang="pt-BR">Brazil's daylight saving time decrees (in 475Portuguese)</a>.</dd> 476<dt>Canada</dt> 477<dd>The Institute for National Measurement Standards publishes current 478and some older information about <a 479href="http://inms-ienm.nrc-cnrc.gc.ca/time_services/daylight_saving_e.html">Time 480Zones & Daylight Saving Time</a>.</dd> 481<dt>Chile</dt> 482<dd>The Chilean Hydrographic and Oceanographic Service publishes a <a 483href="http://www.horaoficial.cl/horaof.htm" hreflang="es"> history of 484official time (in Spanish)</a>.</dd> 485<dt>Germany</dt> 486<dd>The National Institute for Science and Technology maintains the <a 487href="http://www.ptb.de/en/org/4/44/441/dars_e.htm">Realisation of 488Legal Time in Germany</a>.</dd> 489<dt>Israel</dt> 490<dd>The Interior Ministry periodically issues <a 491href="ftp://ftp.cs.huji.ac.il/pub/tz/announcements" 492hreflang="he">announcements (in Hebrew)</a>.</dd> 493<dt>Mexico</dt> 494<dd>The Investigation and Analysis Service of the Mexican Library of 495Congress has published a <a 496href="http://www.cddhcu.gob.mx/bibliot/publica/inveyana/polisoc/horver/" 497hreflang="es">history of Mexican local time (in Spanish)</a>.</dd> 498<dt>Malaysia</dt> 499<dd>See Singapore below.</dd> 500<dt>Netherlands</dt> 501<dd><a href="http://www.phys.uu.nl/~vgent/wettijd/wettijd.htm" 502hreflang="nl">Legal time in the Netherlands (in Dutch)</a> 503covers the history of local time in the Netherlands from ancient times.</dd> 504<dt>New Zealand</dt> 505<dd>The Department of Internal Affairs maintains a brief history <a 506href="http://dia.govt.nz/diawebsite.nsf/wpg_URL/Resource-material-Information-We-Provide-About-Daylight-Saving">About 507Daylight Saving</a>. The privately-maintained <a 508href="http://astrologyschool.com/nztime.html">History of New Zealand 509time</a> has more details.</dd> 510<dt>Norway</dt> 511<dd>The Norwegian Meteorological Institute lists 512<a href="http://met.no/met/met_lex/q_u/sommertid.html" hreflang="no">Summer 513time in Norway (in Norwegian)</a>, citing the 514Institute of Theoretical Astrophysics, Oslo.</dd> 515<dt>Singapore</dt> 516<dd><a 517href="http://www.math.nus.edu.sg/aslaksen/teaching/timezone.html">Why 518is Singapore in the "Wrong" Time Zone?</a> details the 519history of legal time in Singapore and Malaysia.</dd> 520<dt>United Kingdom</dt> 521<dd><a 522href="http://www.srcf.ucam.org/~jsm28/british-time/">History of 523legal time in Britain</a> discusses in detail the country 524with perhaps the best-documented history of clock adjustments. 525The National Physical Laboratory also maintains an <a 526href="http://www.npl.co.uk/server.php?show=ConWebDoc.2714">Archive 527of Summer time dates</a>.</dd> 528</dl> 529<h2>Precision timekeeping</h2> 530<ul> 531<li><a 532href="http://literature.agilent.com/litweb/pdf/5965-7984E.pdf">The 533Science of Timekeeping</a> is a thorough introduction 534to the theory and practice of precision timekeeping.</li> 535<li><a href="http://www.ntp.org/"><abbr 536title="Network Time Protocol">NTP</abbr>: The Network 537Time Protocol</a> 538discusses how to synchronize clocks of 539Internet hosts.</li> 540<li><a 541href="ftp://ftp.rfc-editor.org/in-notes/rfc4833.txt">Timezone 542Options for <abbr title="Dynamic Host Configuration Protocol">DHCP</abbr></a> 543(Internet <abbr>RFC</abbr> 4833) 544specifies a <a 545href="http://www.dhcp.org/">DHCP</a> option for a server to configure 546a client's time zone and daylight saving settings automatically.</li> 547<li><a href="http://gauss.gge.unb.ca/GMT.UT.and.the.RGO.html">A Few 548Facts Concerning <abbr title="Greenwich Mean Time">GMT</abbr>, <abbr 549title="Universal Time">UT</abbr>, and 550the <abbr title="Royal Greenwich Observatory">RGO</abbr></a> 551answers questions like "What is the 552difference between <abbr>GMT</abbr> and <abbr>UTC</abbr>?"</li> 553<li><a 554href="http://www.cv.nrao.edu/~rfisher/Ephemerides/times.html">Astronomical 555Times</a> explains more abstruse astronomical time scales like 556<abbr title="Terrestrial Dynamic Time">TDT</abbr>, 557<abbr title="Geocentric Coordinate Time">TCG</abbr>, and 558<abbr title="Barycentric Dynamic Time">TDB</abbr>. 559<a href="http://www.ucolick.org/~sla/leapsecs/timescales.html">Time 560Scales</a> goes into more detail, particularly for historical variants.</li> 561<li>The <a href="http://iau.org/"><abbr 562title="International Astronomical Union">IAU</abbr></a>'s <a 563href="http://www.iau-sofa.rl.ac.uk/"><abbr 564title="Standards Of Fundamental Astronomy">SOFA</abbr></a> 565initiative publishes Fortran 566code for converting among time scales like 567<abbr title="International Atomic Time">TAI</abbr>, 568<abbr>TDB</abbr>, <abbr>TDT</abbr> and 569<abbr>UTC</abbr>.</li> 570<li><a href="http://jpl.nasa.gov/basics/bsf2-3.htm">Basics of 571Space Flight - Reference Systems - Time Conventions</a> 572briefly explains interplanetary space flight timekeeping.</li> 573<li><a 574href="http://www.giss.nasa.gov/tools/mars24/help/notes.html">Technical 575Notes on Mars Solar Time as Adopted by the Mars24 Sunclock</a> briefly 576describes Mars Coordinated Time (<abbr 577title="Mars Coordinated Time">MTC</abbr>) and the 578diverse local time 579scales used by each landed mission on Mars.</li> 580<li><a href="http://leapsecond.com/">LeapSecond.com</a> is 581dedicated not only to leap seconds but to precise time and frequency 582in general. It covers the state of the art in amateur timekeeping, and 583how the art has progressed over the past few decades.</li> 584<li><a 585href="http://hpiers.obspm.fr/eop-pc/products/bulletins/bulletins.html">Bulletins 586maintained by the 587<abbr title="International Earth Rotation Service">IERS</abbr> 588<abbr title="Earth Orientation Parameters">EOP</abbr> 589(<abbr title="Product Center">PC</abbr>)</a> contains official publications of 590the Earth Orientation Parameters Product Center of the 591International Earth Rotation Service, the committee that decides 592when leap seconds occur.</li> 593<li>The <a 594href="http://six.pairlist.net/mailman/listinfo/leapsecs">Leap 595Second Discussion List</a> covers <a 596href="http://gauss.gge.unb.ca/papers.pdf/gpsworld.november99.pdf">McCarthy 597and Klepczynski's proposal to discontinue leap seconds</a>, 598discussed further in 599<a href="http://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The 600leap second: its history and possible future</a>. 601The (now disbanded) <a href="http://members.aas.org/comms/leap.cfm"><abbr 602title="American Astronomical Society">AAS</abbr> Leap Second 603Committee</a> has solicited input on this proposal. 604<a href="http://www.ucolick.org/~sla/leapsecs/">The 605Future of Leap Seconds</a> covers this 606contentious issue.</li> 607</ul> 608<h2>Time notation</h2> 609<ul> 610<li> 611<a href="http://www.cl.cam.ac.uk/~mgk25/iso-time.html">A Summary of 612the International Standard Date and Time Notation</a> is a good 613summary of 614<a 615href="http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=40874"><abbr 616title="International Organization for Standardization">ISO</abbr> 6178601:2004 -- Data elements and interchange formats -- Information 618interchange -- Representation of dates and times</a>.</li> 619<li> 620<a href="http://www.w3.org/TR/xmlschema-2/#dateTime"><abbr>XML</abbr> 621Schema: Datatypes - dateTime</a> specifies a format inspired by 622<abbr>ISO</abbr> 8601 that is in common use in XML data.</li> 623<li> 624<a href="ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt">Internet 625Message Format</a> (Internet <abbr>RFC</abbr> 2822) §3.3 626specifies the time notation used in email and <a 627href="ftp://ftp.rfc-editor.org/in-notes/rfc2616.txt"><abbr>HTTP</abbr></a> 628headers.</li> 629<li> 630<a href="ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt">Date and Time 631on the Internet: Timestamps</a> (Internet <abbr>RFC</abbr> 3339) 632specifies an <abbr>ISO</abbr> 8601 633profile for use in new Internet 634protocols.</li> 635<li> 636<a href="http://www.hackcraft.net/web/datetime/">Date & Time 637Formats on the Web</a> surveys web- and Internet-oriented date and time 638formats.</li> 639<li> 640<a href="http://exit109.com/~ghealton/y2k/yrexamples.html">The 641Best of Dates, the Worst of Dates</a> covers many problems encountered 642by software developers when handling dates and time stamps.</li> 643<li>The <a 644href="http://unicode.org/cldr/">Unicode Common Locale Data Repository 645(<abbr>CLDR</abbr>) Project</a> has localizations for time zone names, 646abbreviations, identifiers, and formats. For example, it contains 647French translations for "Eastern European Summer Time", "<abbr 648title="Eastern European Summer Time">EEST</abbr>", and 649"Bucharest". <a 650href="http://unicode.org/cldr/data/charts/by_type/names.metazone.html">By-Type 651Chart: names.metazone</a> shows these values for many locales. 652<abbr>ICU</abbr> contains a mechanism for using this data.</li> 653<li>Alphabetic time zone abbreviations should not be used as unique 654identifiers for <abbr>UTC</abbr> offsets as they are ambiguous in 655practice. For example, "<abbr>EST</abbr>" denotes 5 hours behind 656<abbr>UTC</abbr> in English-speaking North America, but it denotes 10 657or 11 hours ahead of <abbr>UTC</abbr> in Australia; and 658French-speaking North Americans prefer 659"<abbr title="Heure Normale de l'Est">HNE</abbr>" to 660"<abbr>EST</abbr>". For <abbr>POSIX</abbr> the <code>tz</code> 661database contains English abbreviations for all time stamps but in 662many cases these are merely inventions of the database 663maintainers.</li> 664<li>Numeric time zone abbreviations typically count hours east of 665<abbr>UTC</abbr>, e.g., <code>+09</code> for Japan and 666<code>-10</code> for Hawaii. However, the <abbr>POSIX</abbr> 667<code>TZ</code> environment variable uses the opposite convention. For 668example, one might use <code>TZ="JST-9"</code> and 669<code>TZ="HST10"</code> for Japan and Hawaii, respectively. If the 670<code>tz</code> database is available, it is usually better to use 671settings like <code>TZ="Asia/Tokyo"</code> and 672<code>TZ="Pacific/Honolulu"</code> instead, as this should avoid 673confusion, handle old time stamps better, and insulate you better from 674any future changes to the rules. One should never set 675<abbr>POSIX</abbr> <code>TZ</code> to a value like 676<code>"GMT-9"</code>, though, since this would falsely claim that 677local time is nine hours ahead of <abbr>UTC</abbr> and the time zone 678is called "<abbr>GMT</abbr>".</li> 679</ul> 680<h2>Related indexes</h2> 681<ul> 682<li><a href="tz-art.htm">Time and the Arts</a></li> 683<li><a href="http://www.dmoz.org/Reference/Time/">Open Directory - 684Reference: Time</a></li> 685<li><a href="http://directory.google.com/Top/Reference/Time/">Google Directory 686- Reference > Time</a></li> 687<li><a href="http://dir.yahoo.com/Science/Measurements_and_Units/Time">Yahoo! 688Directory > Science > Measurements and Units > Time</a></li> 689</ul> 690</body> 691</html> 692