12fe8fb19SBen Gras<!DOCTYPE html 22fe8fb19SBen Gras PUBLIC "-//W3C//DTD HTML 4.01//EN" 32fe8fb19SBen Gras "http://www.w3.org/TR/html4/strict.dtd"> 42fe8fb19SBen Gras<html> 52fe8fb19SBen Gras<head> 62fe8fb19SBen Gras<title>Sources for Time Zone and Daylight Saving Time Data</title> 72fe8fb19SBen Gras<link rel="schema.DC" href="http://purl.org/DC/elements/1.1/"> 8*0a6a1f1dSLionel Sambuc<meta http-equiv="Content-type" content='text/html; charset="UTF-8"'> 92fe8fb19SBen Gras<meta name="DC.Creator" content="Eggert, Paul"> 102fe8fb19SBen Gras<meta name="DC.Contributor" content="Olson, Arthur David"> 11*0a6a1f1dSLionel Sambuc<meta name="DC.Date" content="2015-10-01"> 122fe8fb19SBen Gras<meta name="DC.Description" 132fe8fb19SBen Gras content="Sources of information about time zones and daylight saving time"> 1484d9c625SLionel Sambuc<meta name="DC.Identifier" 1584d9c625SLionel Sambuc content="http://www.iana.org/time-zones/repository/tz-link.htm"> 162fe8fb19SBen Gras<meta name="Keywords" 172fe8fb19SBen Gras content="database,daylight saving,DST,time zone,timezone,tz,zoneinfo"> 182fe8fb19SBen Gras</head> 192fe8fb19SBen Gras<body> 202fe8fb19SBen Gras<h1>Sources for Time Zone and Daylight Saving Time Data</h1> 21*0a6a1f1dSLionel Sambuc<h2>The <code><abbr title="time zone">tz</abbr></code> database</h2> 222fe8fb19SBen Gras<p> 23*0a6a1f1dSLionel SambucThe <a href="https://en.wikipedia.org/wiki/Public_domain">public-domain</a> 242fe8fb19SBen Grastime zone database contains code and data 252fe8fb19SBen Grasthat represent the history of local time 262fe8fb19SBen Grasfor many representative locations around the globe. 272fe8fb19SBen GrasIt is updated periodically to reflect changes made by political bodies 28*0a6a1f1dSLionel Sambucto <a href="https://en.wikipedia.org/wiki/Time_zone">time zone</a> 29*0a6a1f1dSLionel Sambucboundaries and 30*0a6a1f1dSLionel Sambuc<a href="https://en.wikipedia.org/wiki/Daylight_saving_time">daylight-saving</a> 312fe8fb19SBen Grasrules. 32*0a6a1f1dSLionel SambucThis database (often called <code>zoneinfo</code> or 33*0a6a1f1dSLionel Sambuc<code><abbr>tz</abbr></code>) 342fe8fb19SBen Grasis used by several implementations, 352fe8fb19SBen Grasincluding 362fe8fb19SBen Gras<a href="http://www.gnu.org/software/libc/">the 372fe8fb19SBen Gras<abbr title="GNU's Not Unix">GNU</abbr> 3884d9c625SLionel SambucC Library</a> (used in 39*0a6a1f1dSLionel Sambuc<a href="https://en.wikipedia.org/wiki/Linux"><abbr>GNU</abbr>/Linux</a>), 40*0a6a1f1dSLionel Sambuc<a href="http://www.android.com">Android</a>, 41*0a6a1f1dSLionel Sambuc<a href="https://developer.mozilla.org/en-US/Firefox_OS">Firefox 42*0a6a1f1dSLionel Sambuc<abbr title="Operating System">OS</abbr></a>, 43*0a6a1f1dSLionel Sambuc<a href="https://www.freebsd.org">Free<abbr 44*0a6a1f1dSLionel Sambuctitle="Berkeley Software Distribution">BSD</abbr></a>, 45*0a6a1f1dSLionel Sambuc<a href="http://netbsd.org">Net<abbr>BSD</abbr></a>, 46*0a6a1f1dSLionel Sambuc<a href="http://www.openbsd.org">Open<abbr>BSD</abbr></a>, 47*0a6a1f1dSLionel Sambuc<a href="https://cygwin.com">Cygwin</a>, 482fe8fb19SBen Gras<a href="http://www.delorie.com/djgpp/"><abbr 492fe8fb19SBen Grastitle="DJ's GNU Programming Platform">DJGPP</abbr></a>, 50*0a6a1f1dSLionel Sambuc<a href="https://en.wikipedia.org/wiki/MINIX">MINIX</a>, 51*0a6a1f1dSLionel Sambuc<a href="https://en.wikipedia.org/wiki/WebOS"><abbr 52*0a6a1f1dSLionel Sambuctitle="Web Operating System">webOS</abbr></a>, 53*0a6a1f1dSLionel Sambuc<a href="http://ibm.com/aix"><abbr 54*0a6a1f1dSLionel Sambuctitle="Advanced Interactive eXecutive">AIX</abbr></a>, 55*0a6a1f1dSLionel Sambuc<a href="https://en.wikipedia.org/wiki/BlackBerry_10">BlackBerry 10</a>, 56*0a6a1f1dSLionel Sambuc<a href="http://www.apple.com/ios/"><abbr 57*0a6a1f1dSLionel Sambuctitle="iPhone OS">iOS</abbr></a>, 58*0a6a1f1dSLionel Sambuc<a href="http://windows.microsoft.com">Microsoft Windows</a>, 59*0a6a1f1dSLionel Sambuc<a href="http://www8.hp.com/us/en/products/servers/openvms/overview.html">Open<abbr 60*0a6a1f1dSLionel Sambuctitle="Virtual Memory System">VMS</abbr></a>, 61*0a6a1f1dSLionel Sambuc<a href="https://www.oracle.com/database/index.html">Oracle Database</a>, 62*0a6a1f1dSLionel Sambuc<a href="http://oracle.com/solaris">Oracle Solaris</a>, and 63*0a6a1f1dSLionel Sambuc<a href="http://www.apple.com/osx/"><abbr title="Operating System Ten">OS 64*0a6a1f1dSLionel SambucX</abbr></a>.</p> 652fe8fb19SBen Gras<p> 66*0a6a1f1dSLionel SambucEach location in the database represents a region where all 672fe8fb19SBen Grasclocks keeping local time have agreed since 1970. 682fe8fb19SBen GrasLocations are identified by continent or ocean and then by the name of 692fe8fb19SBen Grasthe location, which is typically the largest city within the region. 702fe8fb19SBen GrasFor example, <code>America/New_York</code> 712fe8fb19SBen Grasrepresents most of the <abbr title="United States">US</abbr> eastern time zone; 722fe8fb19SBen Gras<code>America/Phoenix</code> represents most of Arizona, which 732fe8fb19SBen Grasuses mountain time without daylight saving time (<abbr 742fe8fb19SBen Grastitle="daylight saving time">DST</abbr>); 752fe8fb19SBen Gras<code>America/Detroit</code> represents most of Michigan, which uses 762fe8fb19SBen Graseastern time but with different <abbr>DST</abbr> rules in 1975; 772fe8fb19SBen Grasand other entries represent smaller regions like Starke County, 782fe8fb19SBen GrasIndiana, which switched from central to eastern time in 1991 792fe8fb19SBen Grasand switched back in 2006. 802fe8fb19SBen GrasTo use the database on an extended <a 81*0a6a1f1dSLionel Sambuchref="https://en.wikipedia.org/wiki/POSIX"><abbr 822fe8fb19SBen Grastitle="Portable Operating System Interface">POSIX</abbr></a> 83*0a6a1f1dSLionel Sambucimplementation set the <code><abbr>TZ</abbr></code> 84*0a6a1f1dSLionel Sambucenvironment variable to the location's full name, 85*0a6a1f1dSLionel Sambuce.g., <code><abbr>TZ</abbr>="America/New_York"</code>.</p> 862fe8fb19SBen Gras<p> 87*0a6a1f1dSLionel SambucAssociated with each region is a history of offsets from 88*0a6a1f1dSLionel Sambuc<a href="https://en.wikipedia.org/wiki/Universal_Time">Universal 89*0a6a1f1dSLionel SambucTime</a> (<abbr>UT</abbr>), which is <a 90*0a6a1f1dSLionel Sambuchref="https://en.wikipedia.org/wiki/Greenwich_Mean_Time">Greenwich Mean 91*0a6a1f1dSLionel SambucTime</a> (<abbr>GMT</abbr>) with days beginning at midnight; 92*0a6a1f1dSLionel Sambucfor time stamps after 1960 this is more precisely <a 93*0a6a1f1dSLionel Sambuchref="https://en.wikipedia.org/wiki/Coordinated_Universal_Time">Coordinated 94*0a6a1f1dSLionel SambucUniversal Time</a> (<abbr>UTC</abbr>). 95*0a6a1f1dSLionel SambucThe database also records when daylight saving time was in use, 96*0a6a1f1dSLionel Sambucalong with alphabetic time zone abbreviations such as <abbr>EST</abbr> 97*0a6a1f1dSLionel Sambucfor Eastern Standard Time in the <abbr>US</abbr>.</p> 98*0a6a1f1dSLionel Sambuc<p> 99*0a6a1f1dSLionel SambucIn the <code><abbr>tz</abbr></code> database's 100f14fb602SLionel Sambuc<a href="ftp://ftp.iana.org/tz/releases/"><abbr 101f14fb602SLionel Sambuctitle="File Transfer Protocol">FTP</abbr> releases</a> 1022fe8fb19SBen Grasthe code is in the file <code>tzcode<var>C</var>.tar.gz</code>, 1032fe8fb19SBen Graswhere <code><var>C</var></code> is the code's version; 104*0a6a1f1dSLionel Sambucsimilarly, the data entries are in <code>tzdata<var>D</var>.tar.gz</code>, 1052fe8fb19SBen Graswhere <code><var>D</var></code> is the data's version. 106*0a6a1f1dSLionel SambucSince 1996, each version has been a four-digit year followed by 107*0a6a1f1dSLionel Sambuclower-case letter (<samp>a</samp> through <samp>z</samp>, 108*0a6a1f1dSLionel Sambucthen <samp>za</samp> through <samp>zz</samp>, then <samp>zza</samp> 109*0a6a1f1dSLionel Sambucthrough <samp>zzz</samp>, and so on). 110f14fb602SLionel SambucConvenience links to 111f14fb602SLionel Sambucthe <a href="ftp://ftp.iana.org/tz/tzcode-latest.tar.gz">latest 112f14fb602SLionel Sambuccode</a> and 113f14fb602SLionel Sambuc<a href="ftp://ftp.iana.org/tz/tzdata-latest.tar.gz">latest data</a> revisions 11484d9c625SLionel Sambucare also available. 1152fe8fb19SBen GrasThe following <a 116*0a6a1f1dSLionel Sambuchref="https://en.wikipedia.org/wiki/Unix_shell">shell</a> commands download 1172fe8fb19SBen Grasthese files to a <abbr>GNU</abbr>/Linux or similar host; 1182fe8fb19SBen Grassee the downloaded 1192fe8fb19SBen Gras<code>README</code> file for what to do next.</p> 120f14fb602SLionel Sambuc<pre style="margin-left: 2em"><code>mkdir tz 121f14fb602SLionel Sambuccd tz 122f14fb602SLionel Sambuc<a href="http://www.gnu.org/software/wget/">wget</a> --retr-symlinks 'ftp://ftp.iana.org/tz/tz*-latest.tar.gz' 123f14fb602SLionel Sambuc<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 - 124f14fb602SLionel Sambucgzip -dc tzdata-latest.tar.gz | tar -xf - 1252fe8fb19SBen Gras</code></pre> 1262fe8fb19SBen Gras<p> 127f14fb602SLionel SambucThe code and data files can also be obtained from the 12884d9c625SLionel Sambuc<a href="http://www.iana.org/time-zones">Time Zone Database website</a> 12984d9c625SLionel Sambucof the <a href="http://www.iana.org">Internet Assigned Numbers 13084d9c625SLionel SambucAuthority (IANA)</a>. 13184d9c625SLionel SambucAn <a href="https://github.com/eggert/tz">unofficial development 13284d9c625SLionel Sambucrepository</a> of the code and data is available 133*0a6a1f1dSLionel Sambucin <a href="http://git-scm.com">Git</a> form 134*0a6a1f1dSLionel Sambucfrom <a href="https://github.com">GitHub</a>; be careful, as this 13584d9c625SLionel Sambucrepository is less well tested and probably contains more errors. 136f14fb602SLionel Sambuc<p> 137*0a6a1f1dSLionel SambucThe code lets you compile the <code><abbr>tz</abbr></code> source files into 1382fe8fb19SBen Grasmachine-readable binary files, one for each location. It also lets 139*0a6a1f1dSLionel Sambucyou read a <code><abbr>tz</abbr></code> binary file and interpret time stamps for that 1402fe8fb19SBen Graslocation.</p> 1412fe8fb19SBen Gras<p> 142*0a6a1f1dSLionel SambucThe files are by no means authoritative. If you find errors, please 143f14fb602SLionel Sambucsend changes to the <a href="mailto:tz@iana.org">time zone 1442fe8fb19SBen Grasmailing list</a>. You can also <a 1452fe8fb19SBen Grashref="http://news.gmane.org/gmane.comp.time.tz">browse recent 1462fe8fb19SBen Grasmessages</a> sent to the mailing list, <a 14784d9c625SLionel Sambuchref="https://mm.icann.org/mailman/listinfo/tz">subscribe</a> to it, 14884d9c625SLionel Sambucand browse the <a 149f14fb602SLionel Sambuchref="http://mm.icann.org/pipermail/tz/">archive of old 15084d9c625SLionel Sambucmessages</a>. For further information about updates, please see 15184d9c625SLionel Sambuc<a href="http://tools.ietf.org/html/rfc6557">Procedures for 152*0a6a1f1dSLionel SambucMaintaining the Time Zone Database</a> (Internet <abbr 153*0a6a1f1dSLionel Sambuctitle="Request For Comments">RFC</abbr> 6557).</p> 1542fe8fb19SBen Gras<p> 1552fe8fb19SBen GrasThe Web has several other sources for time zone and daylight saving time data. 15684d9c625SLionel SambucHere are some links that may be of interest. 1572fe8fb19SBen Gras</p> 158*0a6a1f1dSLionel Sambuc<h2>Commentary on the <code><abbr>tz</abbr></code> database</h2> 15984d9c625SLionel Sambuc<ul> 16084d9c625SLionel Sambuc<li>The article 161*0a6a1f1dSLionel Sambuc<a href="https://en.wikipedia.org/wiki/Tz_database">tz database</a> is 16284d9c625SLionel Sambucan encyclopedic summary.</li> 163*0a6a1f1dSLionel Sambuc<li><a href="https://web.archive.org/web/20140221080916/http://www.cstdbill.com/tzdb/tz-how-to.html">How to Read the 164*0a6a1f1dSLionel Sambuctz Database Source Files</a> explains the <code><abbr>tz</abbr></code> 165*0a6a1f1dSLionel Sambucdatabase format.</li> 166*0a6a1f1dSLionel Sambuc<li><a 167*0a6a1f1dSLionel Sambuchref="http://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonzoneinfotz-database/">A 16884d9c625SLionel Sambucliterary appreciation of the Olson/Zoneinfo/tz database</a> comments on the 16984d9c625SLionel Sambucdatabase's style.</li> 17084d9c625SLionel Sambuc</ul> 171*0a6a1f1dSLionel Sambuc<h2>Web sites using recent versions of the <code><abbr>tz</abbr></code> database</h2> 1722fe8fb19SBen Gras<p> 1732fe8fb19SBen GrasThese are listed roughly in ascending order of complexity and fanciness. 1742fe8fb19SBen Gras</p> 1752fe8fb19SBen Gras<ul> 176*0a6a1f1dSLionel Sambuc<li><a href="http://time.is">Time.is</a> shows locations' 177*0a6a1f1dSLionel Sambuctime and zones in a simple format.</li> 178*0a6a1f1dSLionel Sambuc<li><a 179*0a6a1f1dSLionel Sambuchref="http://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a> 180*0a6a1f1dSLionel Sambuclets you see the <code><abbr>TZ</abbr></code> values directly.</li> 1812fe8fb19SBen Gras<li><a 1822fe8fb19SBen Grashref="http://convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current 1832fe8fb19SBen GrasTime in 1000 Places</a> uses descriptions of the values.</li> 184*0a6a1f1dSLionel Sambuc<li><a href="http://www.timezoneconverter.com/cgi-bin/tzc.tzc">Time Zone 185*0a6a1f1dSLionel SambucConverter</a> 1862fe8fb19SBen Grasuses a pulldown menu.</li> 187*0a6a1f1dSLionel Sambuc<li><a href="http://home.kpn.nl/vanadovv/time/TZworld.html">Complete 1882fe8fb19SBen Grastimezone information for all countries</a> displays tables of DST rules. 189*0a6a1f1dSLionel Sambuc<li><a href="http://www.timeanddate.com/worldclock/">The World Clock – 1902fe8fb19SBen GrasTime Zones</a> lets you sort zone names and convert times.</li> 191*0a6a1f1dSLionel Sambuc<li><a href="http://www.zeitverschiebung.net/en/">Time Difference</a> 192*0a6a1f1dSLionel Sambuccalculates the current time difference between locations.</li> 193*0a6a1f1dSLionel Sambuc<li><a href="http://www.wx-now.com">Weather Now</a> lists the weather too.</li> 194*0a6a1f1dSLionel Sambuc<li><a href="http://www.thetimenow.com">The Time Now</a> also lists weather.</li> 195*0a6a1f1dSLionel Sambuc<li><a href="http://worldtime.io">worldtime.io</a> 1962fe8fb19SBen Grasalso contains data about time zone boundaries; it supports queries via place 1972fe8fb19SBen Grasnames and shows location maps.</li> 1982fe8fb19SBen Gras</ul> 199*0a6a1f1dSLionel Sambuc<h2>Network protocols for <code><abbr>tz</abbr></code> data</h2> 2002fe8fb19SBen Gras<ul> 201*0a6a1f1dSLionel Sambuc<li>The <a href="http://www.ietf.org">Internet Engineering Task Force</a>'s 202*0a6a1f1dSLionel Sambuc<a href="http://datatracker.ietf.org/wg/tzdist/charter/">Time Zone Data 203*0a6a1f1dSLionel SambucDistribution Service (tzdist) working group</a> is developing a scalable 204*0a6a1f1dSLionel Sambucprotocol for distributing time zone data to clients. It has generated a 205*0a6a1f1dSLionel Sambuca <a href="http://datatracker.ietf.org/doc/draft-ietf-tzdist-service/">draft 206*0a6a1f1dSLionel Sambucprotocol for transferring time zone data</a> and a <a 207*0a6a1f1dSLionel Sambuchref="http://datatracker.ietf.org/doc/draft-ietf-tzdist-caldav-timezone-ref/">draft 208*0a6a1f1dSLionel Sambucprotocol for transferring time zone data by reference</a>. This work is based 209*0a6a1f1dSLionel Sambucon the iCalendar and CalConnect efforts described below.</li> 21084d9c625SLionel Sambuc<li>The <a href="http://tools.ietf.org/html/rfc5545"> 2112fe8fb19SBen GrasInternet Calendaring and Scheduling Core Object Specification 212*0a6a1f1dSLionel Sambuc(iCalendar)</a> (Internet <abbr>RFC</abbr> 5445) 2132fe8fb19SBen Grascovers time zone 2142fe8fb19SBen Grasdata; see its VTIMEZONE calendar component. 215*0a6a1f1dSLionel SambucThe iCalendar format requires specialized parsers and generators; a 216*0a6a1f1dSLionel Sambucvariant <a href="http://tools.ietf.org/html/rfc6321">xCal</a> 217*0a6a1f1dSLionel Sambuc(Internet <abbr>RFC</abbr> 6321) uses 218*0a6a1f1dSLionel Sambuc<a href="http://www.w3.org/XML/"><abbr 219*0a6a1f1dSLionel Sambuctitle="Extensible Markup Language">XML</abbr></a> format, and a variant 220*0a6a1f1dSLionel Sambuc<a href="http://tools.ietf.org/html/rfc7265">jCal</a> 221*0a6a1f1dSLionel Sambuc(Internet <abbr>RFC</abbr> 7265) 222*0a6a1f1dSLionel Sambucuses <a href="http://www.json.org"><abbr 223*0a6a1f1dSLionel Sambuctitle="JavaScript Object Notation">JSON</abbr></a> format. 224*0a6a1f1dSLionel Sambuc<a href="http://calconnect.org">CalConnect, The Calendaring and Scheduling 2252fe8fb19SBen GrasConsortium</a> is promoting further work in this area. <a 2262fe8fb19SBen Grashref="http://calconnect.org/publications/icalendartimezoneproblemsandrecommendationsv1.0.pdf">iCalendar 2272fe8fb19SBen GrasTIMEZONE Problems and Recommendations</a> offers guidelines and 228*0a6a1f1dSLionel Sambucrecommendations for the use of VTIMEZONE and <code><abbr>tz</abbr></code>.</li> 229*0a6a1f1dSLionel Sambuc<li>The <a 2302fe8fb19SBen Grashref="http://calconnect.org/publications/timezoneregistryandservicerecommendationsv1.0.pdf">Timezone 231*0a6a1f1dSLionel SambucRegistry and Service Recommendations</a> of CalConnect's 232*0a6a1f1dSLionel Sambuc<a href="http://calconnect.org/tc-timezone.shtml">TIMEZONE 233*0a6a1f1dSLionel SambucTechnical Committee</a> discusses a 2342fe8fb19SBen Grasstrategy for defining and deploying a time zone 2352fe8fb19SBen Grasregistration process that would establish unique names for each 236*0a6a1f1dSLionel Sambucversion of each <code><abbr>tz</abbr></code> zone, along with a polygonal 2372fe8fb19SBen Grasrepresentation of the geographical area corresponding to the 2382fe8fb19SBen Graszone.</li> 2392fe8fb19SBen Gras<li>The <a 2402fe8fb19SBen Grashref="http://lists.w3.org/Archives/Public/www-rdf-calendar/">www-rdf-calendar</a> 2412fe8fb19SBen Graslist discusses <a 2422fe8fb19SBen Grashref="http://www.w3.org/RDF/"><abbr 2432fe8fb19SBen Grastitle="Resource Description Framework">RDF</abbr></a>-based calendar 2442fe8fb19SBen Grasand group scheduling systems, and has a <a 2452fe8fb19SBen Grashref="http://www.w3.org/2002/12/cal/#tzd">workspace on time zone 246*0a6a1f1dSLionel Sambucdata</a> converted from <code><abbr>tz</abbr></code>.</li> 2472fe8fb19SBen Gras</ul> 248*0a6a1f1dSLionel Sambuc<h2>Other <code><abbr>tz</abbr></code> compilers</h2> 2492fe8fb19SBen Gras<ul> 250*0a6a1f1dSLionel Sambuc<li><a href="http://sourceforge.net/projects/vzic/">Vzic</a> is a <a 251*0a6a1f1dSLionel Sambuchref="https://en.wikipedia.org/wiki/C_%28programming_language%29">C</a> 2522fe8fb19SBen Grasprogram that compiles 253*0a6a1f1dSLionel Sambuc<code><abbr>tz</abbr></code> source into iCalendar-compatible VTIMEZONE files. 2542fe8fb19SBen GrasVzic is freely 2552fe8fb19SBen Grasavailable under the <a 2562fe8fb19SBen Grashref="http://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr> 2572fe8fb19SBen GrasGeneral Public License (<abbr 2582fe8fb19SBen Grastitle="General Public License">GPL</abbr>)</a>.</li> 259*0a6a1f1dSLionel Sambuc<li><a href="http://sourceforge.net/projects/tzical/">tziCal – tz 2602fe8fb19SBen Grasdatabase conversion utility</a> is like Vzic, except for the <a 261*0a6a1f1dSLionel Sambuchref="https://msdn.microsoft.com/netframework">.NET framework</a> 262*0a6a1f1dSLionel Sambucand with a <abbr>BSD</abbr>-style license.</li> 2632fe8fb19SBen Gras<li><a 2642fe8fb19SBen Grashref="http://search.cpan.org/dist/DateTime-TimeZone/">DateTime::TimeZone</a> 2652fe8fb19SBen Grascontains a script <code>parse_olson</code> that compiles 266*0a6a1f1dSLionel Sambuc<code><abbr>tz</abbr></code> source into <a href="http://www.perl.org">Perl</a> 2672fe8fb19SBen Grasmodules. It is part of the Perl <a 268*0a6a1f1dSLionel Sambuchref="http://datetime.perl.org">DateTime Project</a>, which is freely 2692fe8fb19SBen Grasavailable under both the <abbr>GPL</abbr> and the Perl Artistic 2702fe8fb19SBen GrasLicense. DateTime::TimeZone also contains a script 2712fe8fb19SBen Gras<code>tests_from_zdump</code> that generates test cases for each clock 272*0a6a1f1dSLionel Sambuctransition in the <code><abbr>tz</abbr></code> database.</li> 273*0a6a1f1dSLionel Sambuc<li>The <a href="http://howardhinnant.github.io/tz.html">Time Zone 274*0a6a1f1dSLionel SambucDatabase Parser</a> is a 275*0a6a1f1dSLionel Sambuc<a href="https://en.wikipedia.org/wiki/C%2B%2B">C++</a> parser and 276*0a6a1f1dSLionel Sambucruntime library. It is freely available under the 277*0a6a1f1dSLionel Sambuc<a href="http://creativecommons.org/licenses/by/4.0/">Creative Commons 278*0a6a1f1dSLionel SambucAttribution 4.0 International Public License</a>.</li> 279*0a6a1f1dSLionel Sambuc<li><a href="http://site.icu-project.org">International Components for 2802fe8fb19SBen GrasUnicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a 281*0a6a1f1dSLionel Sambuchref="https://en.wikipedia.org/wiki/Java_%28programming_language%29">Java</a> 2822fe8fb19SBen Graslibraries for internationalization that 283*0a6a1f1dSLionel Sambuchas a compiler from <code><abbr>tz</abbr></code> source 284*0a6a1f1dSLionel Sambucand from <abbr title="Common Locale Data Repository">CLDR</abbr> data 285*0a6a1f1dSLionel Sambuc(mentioned below) 2862fe8fb19SBen Grasinto an <abbr>ICU</abbr>-specific format. 2872fe8fb19SBen Gras<abbr>ICU</abbr> is freely available under a 288*0a6a1f1dSLionel Sambuc<abbr>BSD</abbr>-style license.</li> 289*0a6a1f1dSLionel Sambuc<li>The <a 290*0a6a1f1dSLionel Sambuchref="http://www.oracle.com/technetwork/java/javase/tzupdater-readme-136440.html">TZUpdater 291*0a6a1f1dSLionel Sambuctool</a> compiles <code><abbr>tz</abbr></code> source into the format used by 292*0a6a1f1dSLionel SambucOracle Java.</li> 293*0a6a1f1dSLionel Sambuc<li><a href="http://www.joda.org/joda-time/">Joda-Time – Java date 2942fe8fb19SBen Grasand time <abbr title="Application Program Interface">API</abbr></a> 2952fe8fb19SBen Grascontains a class 2962fe8fb19SBen Gras<code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles 297*0a6a1f1dSLionel Sambuc<code><abbr>tz</abbr></code> source into a Joda-specific binary format. Joda Time 2982fe8fb19SBen Grasis freely available under a <abbr>BSD</abbr>-style license.</li> 299*0a6a1f1dSLionel Sambuc<li><a href="http://nodatime.org">Noda Time – Date and time API for 300*0a6a1f1dSLionel Sambuc.NET</a> and <a href="http://www.babiej.demon.nl/Tz4Net/main.htm">TZ4Net</a> 301*0a6a1f1dSLionel Sambucare similar to Joda Time, but for the .NET framework instead of 302*0a6a1f1dSLionel SambucJava. They are freely available under the 303*0a6a1f1dSLionel Sambuc<a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License</a> 304*0a6a1f1dSLionel Sambucand a <abbr>BSD</abbr>-style license, respectively.</li> 305*0a6a1f1dSLionel Sambuc<li><a href="https://en.wikipedia.org/wiki/JavaScript">JavaScript</a>-based 306*0a6a1f1dSLionel Sambuccompilers and libraries include: 307*0a6a1f1dSLionel Sambuc<ul> 308*0a6a1f1dSLionel Sambuc<li><a href="http://momentjs.com/timezone/">Moment Timezone</a> is a 309*0a6a1f1dSLionel Sambucplugin for the <a href="http://momentjs.com">Moment.js</a> date 310*0a6a1f1dSLionel Sambucmanipulation library. It is freely available under 311*0a6a1f1dSLionel Sambucthe <abbr title="Massachusetts Institute of Technology">MIT</abbr> 312*0a6a1f1dSLionel Sambuclicense.</li> 313*0a6a1f1dSLionel Sambuc<li><a href="https://github.com/mde/timezone-js">TimezoneJS.Date</a>'s 314*0a6a1f1dSLionel Sambuc<abbr>API</abbr> is upward compatible with standard JavaScript 315*0a6a1f1dSLionel SambucDates. It is freely available under the Apache License.</li> 316*0a6a1f1dSLionel Sambuc<li><a href="https://github.com/sproutsocial/walltime-js">Walltime-js</a> 317*0a6a1f1dSLionel Sambuctranslates <abbr>UT</abbr> to local time. It is freely available under 318*0a6a1f1dSLionel Sambucthe <abbr>MIT</abbr> license.</li> 319*0a6a1f1dSLionel Sambuc</ul> 320*0a6a1f1dSLionel Sambuc<li><a href="http://pytz.sourceforge.net">pytz – World Timezone 321*0a6a1f1dSLionel SambucDefinitions for Python</a> compiles <code><abbr>tz</abbr></code> source into 322*0a6a1f1dSLionel Sambuc<a href="https://www.python.org">Python</a>. 3232fe8fb19SBen GrasIt is freely available under a <abbr>BSD</abbr>-style license.</li> 324*0a6a1f1dSLionel Sambuc<li><a href="http://tzinfo.github.io">TZInfo – 325*0a6a1f1dSLionel SambucRuby Timezone Library</a> 326*0a6a1f1dSLionel Sambuccompiles <code><abbr>tz</abbr></code> source into 327*0a6a1f1dSLionel Sambuc<a href="https://www.ruby-lang.org/en/">Ruby</a>. 328*0a6a1f1dSLionel SambucIt is freely available under the <abbr>MIT</abbr> license.</li> 32984d9c625SLionel Sambuc<li>The <a href="http://www.squeaksource.com/Chronos/">Chronos Date/Time 33084d9c625SLionel SambucLibrary</a> is 331*0a6a1f1dSLionel Sambuca <a href="https://en.wikipedia.org/wiki/Smalltalk">Smalltalk</a> class 332*0a6a1f1dSLionel Sambuclibrary that compiles <code><abbr>tz</abbr></code> source into a time 333*0a6a1f1dSLionel Sambuczone repository whose format 334*0a6a1f1dSLionel Sambucis either proprietary or an <abbr>XML</abbr>-encoded 3352fe8fb19SBen Grasrepresentation.</li> 336*0a6a1f1dSLionel Sambuc<li><a href="http://tcl.tk">Tcl</a> 337*0a6a1f1dSLionel Sambuccontains a developer-oriented parser that compiles <code><abbr>tz</abbr></code> 3382fe8fb19SBen Grassource into text files, along with a runtime that can read those 3392fe8fb19SBen Grasfiles. Tcl is freely available under a <abbr>BSD</abbr>-style 3402fe8fb19SBen Graslicense.</li> 3412fe8fb19SBen Gras</ul> 342*0a6a1f1dSLionel Sambuc<h2>Other <code><abbr>tz</abbr></code> binary file readers</h2> 3432fe8fb19SBen Gras<ul> 3442fe8fb19SBen Gras<li>The <a 3452fe8fb19SBen Grashref="http://www.gnu.org/software/libc/"><abbr>GNU</abbr> C 3462fe8fb19SBen GrasLibrary</a> 3472fe8fb19SBen Grashas an independent, thread-safe implementation of 348*0a6a1f1dSLionel Sambuca <code><abbr>tz</abbr></code> binary file reader. 3492fe8fb19SBen GrasThis library is freely available under the 3502fe8fb19SBen Gras<a href="http://www.gnu.org/copyleft/lesser.html"> 3512fe8fb19SBen Gras<abbr>GNU</abbr> Lesser General Public License 3522fe8fb19SBen Gras(<abbr title="Lesser General Public License">LGPL</abbr>)</a>, 3532fe8fb19SBen Grasand is widely used in <abbr>GNU</abbr>/Linux systems.</li> 354*0a6a1f1dSLionel Sambuc<li><a href="https://www.gnome.org">GNOME</a>'s Glib has 355*0a6a1f1dSLionel Sambuca <code><abbr>tz</abbr></code> binary file reader written in C that 356*0a6a1f1dSLionel Sambuccreates a <code>GTimeZone</code> object representing sets 357*0a6a1f1dSLionel Sambucof <abbr>UT</abbr> offsets. 3582fe8fb19SBen GrasIt is freely available under the <abbr>LGPL</abbr>.</li> 359*0a6a1f1dSLionel Sambuc<li><a href="http://bmsi.com/java/#TZ">ZoneInfo.java</a> 360*0a6a1f1dSLionel Sambucis a <code><abbr>tz</abbr></code> binary file reader written in Java. 361*0a6a1f1dSLionel SambucIt is freely available under the <abbr>LGPL</abbr>.</li> 362*0a6a1f1dSLionel Sambuc<li><a href="https://github.com/bigeasy/timezone">Timezone</a> is a 363*0a6a1f1dSLionel SambucJavaScript library that supports date arithmetic that is time zone 364*0a6a1f1dSLionel Sambucaware. It is freely available under the <abbr>MIT</abbr> license.</li> 3652fe8fb19SBen Gras<li>Tcl, mentioned above, also contains a 366*0a6a1f1dSLionel Sambuc<code><abbr>tz</abbr></code> binary file reader.</li> 36784d9c625SLionel Sambuc<li><a href="http://search.cpan.org/perldoc?DateTime::TimeZone::Tzfile"> 36884d9c625SLionel SambucDateTime::TimeZone::Tzfile</a> 369*0a6a1f1dSLionel Sambucis a <code><abbr>tz</abbr></code> binary file reader written in Perl. 37084d9c625SLionel SambucIt is freely available under the same terms as Perl 37184d9c625SLionel Sambuc(dual <abbr>GPL</abbr> and Artistic license).</li> 37284d9c625SLionel Sambuc<li>The 37384d9c625SLionel Sambucpublic-domain <a href="https://github.com/dbaron/tz.js">tz.js</a> 374*0a6a1f1dSLionel Sambuclibrary contains a Python tool that 375*0a6a1f1dSLionel Sambucconverts <code><abbr>tz</abbr></code> binary data into 376*0a6a1f1dSLionel Sambuc<abbr>JSON</abbr>-format data suitable for use 377*0a6a1f1dSLionel Sambucin its JavaScript library for time zone conversion. Dates before 1970 37884d9c625SLionel Sambucare not supported.</li> 379*0a6a1f1dSLionel Sambuc<li>The <a 380*0a6a1f1dSLionel Sambuchref="http://hackage.haskell.org/package/timezone-olson">timezone-olson</a> 381*0a6a1f1dSLionel Sambucpackage contains <a href="http://haskell.org">Haskell</a> code that 382*0a6a1f1dSLionel Sambucparses and uses <code><abbr>tz</abbr></code> binary data. It is freely 383*0a6a1f1dSLionel Sambucavailable under a BSD-style license.</li> 3842fe8fb19SBen Gras</ul> 385*0a6a1f1dSLionel Sambuc<h2>Other <code><abbr>tz</abbr></code>-based time zone software</h2> 3862fe8fb19SBen Gras<ul> 387*0a6a1f1dSLionel Sambuc<li><a href="https://foxclocks.org">FoxClocks</a> 388*0a6a1f1dSLionel Sambucis an extension for <a href="http://www.google.com/chrome/">Google 38984d9c625SLionel SambucChrome</a> and for <a 390*0a6a1f1dSLionel Sambuchref="https://developer.mozilla.org/en-US/docs/Mozilla/Tech/Toolkit_API">Mozilla 3912fe8fb19SBen GrasToolkit</a> applications like <a 392*0a6a1f1dSLionel Sambuchref="https://www.mozilla.org/en-US/firefox/new/">Firefox</a> and <a 393*0a6a1f1dSLionel Sambuchref="https://www.mozilla.org/en-US/thunderbird/">Thunderbird</a>. 3942fe8fb19SBen GrasIt displays multiple clocks in the application window, and has a mapping 395*0a6a1f1dSLionel Sambucinterface to <a href="http://www.google.com/earth/">Google Earth</a>. 3962fe8fb19SBen GrasIt is freely available under the <abbr>GPL</abbr>.</li> 397*0a6a1f1dSLionel Sambuc<li><a href="http://golang.org">Go programming language</a> 398*0a6a1f1dSLionel Sambucimplementations contain a copy of a 32-bit subset of a recent 399*0a6a1f1dSLionel Sambuc<code><abbr>tz</abbr></code> database in a 400*0a6a1f1dSLionel SambucGo-specific format.</li> 4012fe8fb19SBen Gras<li><a 4022fe8fb19SBen Grashref="http://users.skynet.be/Peter.Verthez/projects/intclock/">International 403*0a6a1f1dSLionel Sambucclock (intclock)</a> is a clock that displays multiple time zones on 4042fe8fb19SBen Gras<abbr>GNU</abbr>/Linux and similar systems. It is freely available 4052fe8fb19SBen Grasunder the <abbr>GPL</abbr>.</li> 406*0a6a1f1dSLionel Sambuc<li>Microsoft Windows 8.1 407*0a6a1f1dSLionel Sambucand later has <code><abbr>tz</abbr></code> data and <abbr>CLDR</abbr> 408*0a6a1f1dSLionel Sambucdata (mentioned below) used by 409*0a6a1f1dSLionel Sambuc<a href="https://en.wikipedia.org/wiki/Windows_Runtime">Windows Runtime</a> 410*0a6a1f1dSLionel Sambucclasses such as <a 411*0a6a1f1dSLionel Sambuchref="https://msdn.microsoft.com/en-us/library/windows/apps/windows.globalization.datetimeformatting.datetimeformatter.aspx"><code>DateTimeFormatter</code></a>. 412*0a6a1f1dSLionel Sambuc<a 413*0a6a1f1dSLionel Sambuchref="http://blogs.msdn.com/b/bclteam/archive/2007/06/07/exploring-windows-time-zones-with-system-timezoneinfo-josh-free.aspx">Exploring 414*0a6a1f1dSLionel SambucWindows Time Zones with <code>System.TimeZoneInfo</code></a> describes 415*0a6a1f1dSLionel Sambucthe older, proprietary method of Microsoft Windows 2000 and later, 416*0a6a1f1dSLionel Sambucwhich stores time zone data in the 417*0a6a1f1dSLionel Sambuc<a href="https://en.wikipedia.org/wiki/Windows_Registry">Windows Registry</a>. The 418*0a6a1f1dSLionel Sambuc<a 419*0a6a1f1dSLionel Sambuchref="http://www.unicode.org/cldr/charts/latest/supplemental/zone_tzid.html">Zone → 420*0a6a1f1dSLionel SambucTzid table</a> or <a 421*0a6a1f1dSLionel Sambuchref="http://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml"><abbr>XML</abbr> 422*0a6a1f1dSLionel Sambucfile</a> of the <abbr>CLDR</abbr> data maps proprietary zone IDs 423*0a6a1f1dSLionel Sambucto <code><abbr>tz</abbr></code> names. 424*0a6a1f1dSLionel Sambuc<li><a 425*0a6a1f1dSLionel Sambuchref="https://www.oracle.com/java/index.html">Oracle 426*0a6a1f1dSLionel SambucJava</a> contains a copy of a subset of a recent 427*0a6a1f1dSLionel Sambuc<code><abbr>tz</abbr></code> database in a 4282fe8fb19SBen GrasJava-specific format.</li> 429*0a6a1f1dSLionel Sambuc<li><a href="https://kimmo.suominen.com/sw/timezone/">Time Zone</a> is 430*0a6a1f1dSLionel Sambuca <a href="https://wordpress.org">WordPress</a> plugin. It is freely 4312fe8fb19SBen Grasavailable under a <abbr>BSD</abbr>-style license.</li> 43284d9c625SLionel Sambuc<li><a href="http://www.relativedata.com/time-zone-master">Time Zone 43384d9c625SLionel SambucMaster</a> is a Microsoft Windows clock program that can automatically 43484d9c625SLionel Sambucdownload, compile and use the <code>tzdata<var>D</var>.tar.gz</code> 43584d9c625SLionel Sambucfiles as they are released. The Basic version is free.</li> 4362fe8fb19SBen Gras<li><a 4372fe8fb19SBen Grashref="http://veladg.com/velaterra.html">VelaTerra</a> is 438*0a6a1f1dSLionel Sambucan <abbr>OS X</abbr> program. Its developers 4392fe8fb19SBen Gras<a href="http://veladg.com/tzoffer.html">offer free 440*0a6a1f1dSLionel Sambuclicenses</a> to <code><abbr>tz</abbr></code> contributors.</li> 4412fe8fb19SBen Gras</ul> 4422fe8fb19SBen Gras<h2>Other time zone databases</h2> 4432fe8fb19SBen Gras<ul> 4442fe8fb19SBen Gras<li><a href="http://www.astro.com/cgi/aq.cgi">Atlas Query</a> 44584d9c625SLionel Sambucis Astrodienst's Web version of Shanks and Pottenger's 44684d9c625SLionel Sambuctime zone history atlases published in both <a 44784d9c625SLionel Sambuchref="http://astrocom.com/astrology-products/software/acs-atlas-software">computer</a> 4482fe8fb19SBen Grasand book form (<a 44984d9c625SLionel Sambuchref="http://www.astrocom.com/astrology/books/american-atlas">one volume 450*0a6a1f1dSLionel Sambucfor the <abbr>US</abbr></a>, and <a 45184d9c625SLionel Sambuchref="http://www.astrocom.com/astrology/books/international-atlas">one for 4522fe8fb19SBen Grasother locations</a>) by <a 453*0a6a1f1dSLionel Sambuchref="http://astrocom.com">Astro Computing Services</a>. 454*0a6a1f1dSLionel SambucThese atlases are extensive but unreliable, as Shanks appears to have 455*0a6a1f1dSLionel Sambucguessed many <abbr>UT</abbr> offsets and transitions. The atlases cite no 456*0a6a1f1dSLionel Sambucsources and do not indicate which entries are guesswork.</li> 457*0a6a1f1dSLionel Sambuc<li><a href="https://en.wikipedia.org/wiki/HP-UX">HP-UX</a> has a database in 458*0a6a1f1dSLionel Sambucits own <code>tztab</code>(4) format.</li> 459*0a6a1f1dSLionel Sambuc<li>Microsoft Windows has proprietary data mentioned above.</li> 460*0a6a1f1dSLionel Sambuc<li><a href="http://www.worldtimeserver.com">World Time Server</a> 4612fe8fb19SBen Grasis another time zone database.</li> 4622fe8fb19SBen Gras<li><a href="http://tycho.usno.navy.mil/tzones.html">World Time Zones</a> 4632fe8fb19SBen Grascontains data from the Time Service Department of the 464*0a6a1f1dSLionel Sambuc<abbr>US</abbr> Naval Observatory.</li> 46584d9c625SLionel Sambuc<li>The <a href="http://www.iata.org/publications/Pages/ssim.aspx">Standard 4662fe8fb19SBen GrasSchedules Information Manual</a> of the 467*0a6a1f1dSLionel SambucInternational Air Transport Association 4682fe8fb19SBen Grasgives current time zone rules for airports served by commercial aviation.</li> 4692fe8fb19SBen Gras</ul> 4702fe8fb19SBen Gras<h2>Maps</h2> 4712fe8fb19SBen Gras<ul> 472*0a6a1f1dSLionel Sambuc<li>The <a href="https://www.cia.gov/index.html">United States Central 4732fe8fb19SBen GrasIntelligence Agency (<abbr 4742fe8fb19SBen Grastitle="Central Intelligence Agency">CIA</abbr>)</a> publishes a <a 47584d9c625SLionel Sambuchref="https://www.cia.gov/library/publications/the-world-factbook/graphics/ref_maps/physical/pdf/standard_time_zones_of_the_world.pdf">time 4762fe8fb19SBen Graszone map</a>; the 4772fe8fb19SBen Gras<a 478*0a6a1f1dSLionel Sambuchref="http://www.lib.utexas.edu/maps/world.html">Perry–Castañeda 4792fe8fb19SBen GrasLibrary Map Collection</a> 4802fe8fb19SBen Grasof the University of Texas at Austin has copies of 4812fe8fb19SBen Grasrecent editions. 4822fe8fb19SBen GrasThe pictorial quality is good, 4832fe8fb19SBen Grasbut the maps do not indicate summer time, 4842fe8fb19SBen Grasand parts of the data are a few years out of date.</li> 485*0a6a1f1dSLionel Sambuc<li><a href="http://www.worldtimezone.com">Current time around the world 4862fe8fb19SBen Grasand standard time zones map of the world</a> 4872fe8fb19SBen Grashas several fancy time zone maps; it covers Russia particularly well. 4882fe8fb19SBen GrasThe maps' pictorial quality is not quite as good as the 4892fe8fb19SBen Gras<abbr>CIA</abbr>'s 4902fe8fb19SBen Grasbut the maps are more up to date.</li> 491*0a6a1f1dSLionel Sambuc<li><a 492*0a6a1f1dSLionel Sambuchref="http://blog.poormansmath.net/how-much-is-time-wrong-around-the-world/">How 493*0a6a1f1dSLionel Sambucmuch is time wrong around the world?</a> maps the difference between 494*0a6a1f1dSLionel Sambucmean solar and standard time, highlighting areas such as western China 495*0a6a1f1dSLionel Sambucwhere the two differ greatly. It's a bit out of date, unfortunately.</li> 4962fe8fb19SBen Gras</ul> 4972fe8fb19SBen Gras<h2>Time zone boundaries</h2> 4982fe8fb19SBen Gras<ul> 499*0a6a1f1dSLionel Sambuc<li><a href="http://efele.net/maps/tz/"><abbr>TZ</abbr> timezones 500*0a6a1f1dSLionel Sambucmaps</a> contains <a 501*0a6a1f1dSLionel Sambuchref="https://en.wikipedia.org/wiki/Shapefile">shapefiles</a> of 502*0a6a1f1dSLionel Sambucsets of <code><abbr>tz</abbr></code> regions.</li> 503*0a6a1f1dSLionel Sambuc<li>The <a href="https://github.com/bradfitz/latlong">latlong package</a> 504*0a6a1f1dSLionel Sambucmaps geographical coordinates to a <code><abbr>tz</abbr></code> region. 505*0a6a1f1dSLionel SambucIt is written in Go and is freely available under the Apache License.</li> 50684d9c625SLionel Sambuc<li><a href="http://derickrethans.nl/what-time-is-it.html">What Time 507*0a6a1f1dSLionel Sambucis It Here?</a> applies <a href="http://www.mongodb.org">MongoDB</a> 50884d9c625SLionel Sambucgeospatial query operators to shapefiles' data.</li> 50984d9c625SLionel Sambuc<li><a href="http://statoids.com/statoids.html">Administrative 51084d9c625SLionel SambucDivisions of Countries ("Statoids")</a> contains lists of 51184d9c625SLionel Sambucpolitical subdivision data related to time zones.</li> 512*0a6a1f1dSLionel Sambuc<li><a href="http://home.kpn.nl/vanadovv/time/Multizones.html">Time 5132fe8fb19SBen Graszone boundaries for multizone countries</a> summarizes legal 5142fe8fb19SBen Grasboundaries between time zones within countries.</li> 5152fe8fb19SBen Gras<li>Manifold.net's <a 51684d9c625SLionel Sambuchref="http://manifold.net/info/freestuff.shtml">Free Stuff for 51784d9c625SLionel SambucManifold System Users</a> includes a Manifold-format map of 5182fe8fb19SBen Grasworld time zone boundaries distributed under the 5192fe8fb19SBen Gras<abbr>GPL</abbr>.</li> 5202fe8fb19SBen Gras<li>The GeoCommunity lists several commercial sources for <a 5212fe8fb19SBen Grashref="http://spatialnews.geocomm.com/features/timezones/">International 5222fe8fb19SBen GrasTime Zones and Time Zone Data</a>.</li> 5232fe8fb19SBen Gras<li>A ship within the <a 524*0a6a1f1dSLionel Sambuchref="https://en.wikipedia.org/wiki/Territorial_waters">territorial 5252fe8fb19SBen Graswaters</a> of any nation uses that nation's time. In international 5262fe8fb19SBen Graswaters, time zone boundaries are meridians 15° apart, except that 527*0a6a1f1dSLionel Sambuc<abbr>UTC</abbr>−12 and <abbr>UTC</abbr>+12 are each 7.5° 528*0a6a1f1dSLionel Sambucwide and are separated by 5292fe8fb19SBen Grasthe 180° meridian (not by the International Date Line, which is 5302fe8fb19SBen Grasfor land and territorial waters only). A captain can change ship's 5312fe8fb19SBen Grasclocks any time after entering a new time zone; midnight changes are 5322fe8fb19SBen Grascommon.</li> 5332fe8fb19SBen Gras</ul> 5342fe8fb19SBen Gras<h2>Civil time concepts and history</h2> 5352fe8fb19SBen Gras<ul> 536*0a6a1f1dSLionel Sambuc<li><a href="http://www.nist.gov/pml/general/time/index.cfm">A 5372fe8fb19SBen GrasWalk through Time</a> 5382fe8fb19SBen Grassurveys the evolution of timekeeping.</li> 539*0a6a1f1dSLionel Sambuc<li><a href="http://www.webexhibits.org/daylightsaving/">About Daylight 540*0a6a1f1dSLionel SambucSaving Time – History, rationale, laws & dates</a> 5412fe8fb19SBen Grasis an overall history of <abbr>DST</abbr>.</li> 54284d9c625SLionel Sambuc<li><a href="http://www.w3.org/TR/timezone/">Working with Time Zones</a> 54384d9c625SLionel Sambuccontains guidelines and best practices for software applications that 54484d9c625SLionel Sambucdeal with civil time.</li> 5452fe8fb19SBen Gras<li><a href="http://energy.ca.gov/daylightsaving.html">Saving Time, 5462fe8fb19SBen GrasSaving Energy</a> discusses a primary justification for <abbr>DST</abbr>.</li> 54784d9c625SLionel Sambuc<li><a href="http://seizethedaylight.com/dst/">A Brief 5482fe8fb19SBen GrasHistory of Daylight Saving Time</a> summarizes some of the contentious 5492fe8fb19SBen Grashistory of <abbr>DST</abbr>.</li> 55084d9c625SLionel Sambuc<li><a href="http://www.staff.science.uu.nl/~gent0113/idl/idl.htm">A History of 5512fe8fb19SBen Grasthe International Date Line</a> tells the story of the most important 5522fe8fb19SBen Grastime zone boundary.</li> 5532fe8fb19SBen Gras<li><a href="http://statoids.com/tconcept.html">Basic Time 5542fe8fb19SBen GrasZone Concepts</a> discusses terminological issues behind time zones.</li> 5552fe8fb19SBen Gras</ul> 5562fe8fb19SBen Gras<h2>National histories of legal time</h2> 5572fe8fb19SBen Gras<dl> 5582fe8fb19SBen Gras<dt>Australia</dt> 559*0a6a1f1dSLionel Sambuc<dd>The Parliamentary Library has commissioned a <a 560*0a6a1f1dSLionel Sambuchref="http://www.aph.gov.au/binaries/library/pubs/rp/2009-10/10rp10.pdf">research 561*0a6a1f1dSLionel Sambucpaper on daylight saving time in Australia</a>. 562*0a6a1f1dSLionel SambucThe Bureau of Meteorology publishes a list of <a 563*0a6a1f1dSLionel Sambuchref="http://www.bom.gov.au/climate/averages/tables/dst_times.shtml">Implementation 564*0a6a1f1dSLionel SambucDates of Daylight Savings Time within Australia</a>.</dd> 5652fe8fb19SBen Gras<dt>Belgium</dt> 5662fe8fb19SBen Gras<dd>The Royal Observatory of Belgium maintains a table of <a 5672fe8fb19SBen Grashref="http://www.astro.oma.be/GENERAL/INFO/nli001a.html" 5682fe8fb19SBen Grashreflang="nl">time in Belgium (in Dutch)</a>.</dd> 5692fe8fb19SBen Gras<dt>Brazil</dt> 5702fe8fb19SBen Gras<dd>The Time Service Department of the National Observatory 5712fe8fb19SBen Grasrecords <a href="http://pcdsh01.on.br/DecHV.html" 5722fe8fb19SBen Grashreflang="pt-BR">Brazil's daylight saving time decrees (in 5732fe8fb19SBen GrasPortuguese)</a>.</dd> 5742fe8fb19SBen Gras<dt>Canada</dt> 57584d9c625SLionel Sambuc<dd>National Research Council Canada publishes current 5762fe8fb19SBen Grasand some older information about <a 57784d9c625SLionel Sambuchref="http://www.nrc-cnrc.gc.ca/eng/services/time/time_zones.html">time 57884d9c625SLionel Sambuczones & daylight saving time</a>.</dd> 5792fe8fb19SBen Gras<dt>Chile</dt> 580*0a6a1f1dSLionel Sambuc<dd>The Hydrographic and Oceanographic Service of the Chilean Navy publishes a 581*0a6a1f1dSLionel Sambuc<a href="http://www.horaoficial.cl/historia_hora.html" hreflang="es">history of 582*0a6a1f1dSLionel SambucChile's official time (in Spanish)</a>.</dd> 5832fe8fb19SBen Gras<dt>Germany</dt> 5842fe8fb19SBen Gras<dd>The National Institute for Science and Technology maintains the <a 585*0a6a1f1dSLionel Sambuchref="http://www.ptb.de/cms/en/fachabteilungen/abt4/fb-44/ag-441/realisation-of-legal-time-in-germany.html">Realisation 586*0a6a1f1dSLionel Sambucof Legal Time in Germany</a>.</dd> 5872fe8fb19SBen Gras<dt>Israel</dt> 5882fe8fb19SBen Gras<dd>The Interior Ministry periodically issues <a 5892fe8fb19SBen Grashref="ftp://ftp.cs.huji.ac.il/pub/tz/announcements" 5902fe8fb19SBen Grashreflang="he">announcements (in Hebrew)</a>.</dd> 5912fe8fb19SBen Gras<dt>Mexico</dt> 5922fe8fb19SBen Gras<dd>The Investigation and Analysis Service of the Mexican Library of 5932fe8fb19SBen GrasCongress has published a <a 594*0a6a1f1dSLionel Sambuchref="http://www.diputados.gob.mx/bibliot/publica/inveyana/polisoc/horver/index.htm" 5952fe8fb19SBen Grashreflang="es">history of Mexican local time (in Spanish)</a>.</dd> 5962fe8fb19SBen Gras<dt>Malaysia</dt> 5972fe8fb19SBen Gras<dd>See Singapore below.</dd> 5982fe8fb19SBen Gras<dt>Netherlands</dt> 59984d9c625SLionel Sambuc<dd><a href="http://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm" 6002fe8fb19SBen Grashreflang="nl">Legal time in the Netherlands (in Dutch)</a> 6012fe8fb19SBen Grascovers the history of local time in the Netherlands from ancient times.</dd> 6022fe8fb19SBen Gras<dt>New Zealand</dt> 60384d9c625SLionel Sambuc<dd>The Department of Internal Affairs maintains a brief <a 60484d9c625SLionel Sambuchref="http://www.dia.govt.nz/Daylight-Saving-History">History of 6052fe8fb19SBen GrasDaylight Saving</a>. The privately-maintained <a 6062fe8fb19SBen Grashref="http://astrologyschool.com/nztime.html">History of New Zealand 6072fe8fb19SBen Grastime</a> has more details.</dd> 6082fe8fb19SBen Gras<dt>Singapore</dt> 6092fe8fb19SBen Gras<dd><a 6102fe8fb19SBen Grashref="http://www.math.nus.edu.sg/aslaksen/teaching/timezone.html">Why 6112fe8fb19SBen Grasis Singapore in the "Wrong" Time Zone?</a> details the 6122fe8fb19SBen Grashistory of legal time in Singapore and Malaysia.</dd> 6132fe8fb19SBen Gras<dt>United Kingdom</dt> 6142fe8fb19SBen Gras<dd><a 61584d9c625SLionel Sambuchref="http://www.polyomino.org.uk/british-time/">History of 6162fe8fb19SBen Graslegal time in Britain</a> discusses in detail the country 6172fe8fb19SBen Graswith perhaps the best-documented history of clock adjustments. 6182fe8fb19SBen GrasThe National Physical Laboratory also maintains an <a 61984d9c625SLionel Sambuchref="http://www.npl.co.uk/educate-explore/what-is-time/archive-of-summer-time-dates-1916-2006">Archive 6202fe8fb19SBen Grasof Summer time dates</a>.</dd> 621*0a6a1f1dSLionel Sambuc<dt>United States</dt> 622*0a6a1f1dSLionel Sambuc<dd>The Department of Transportation's <a 623*0a6a1f1dSLionel Sambuchref="http://www.transportation.gov/regulations/recent-time-zone-proceedings">Recent 624*0a6a1f1dSLionel SambucTime Zone Proceedings</a> lists changes to time zone boundaries.</dd> 6252fe8fb19SBen Gras</dl> 6262fe8fb19SBen Gras<h2>Precision timekeeping</h2> 6272fe8fb19SBen Gras<ul> 6282fe8fb19SBen Gras<li><a 6292fe8fb19SBen Grashref="http://literature.agilent.com/litweb/pdf/5965-7984E.pdf">The 6302fe8fb19SBen GrasScience of Timekeeping</a> is a thorough introduction 6312fe8fb19SBen Grasto the theory and practice of precision timekeeping.</li> 632*0a6a1f1dSLionel Sambuc<li><a href="http://www.ntp.org"><abbr 6332fe8fb19SBen Grastitle="Network Time Protocol">NTP</abbr>: The Network 6342fe8fb19SBen GrasTime Protocol</a> 6352fe8fb19SBen Grasdiscusses how to synchronize clocks of 6362fe8fb19SBen GrasInternet hosts.</li> 637*0a6a1f1dSLionel Sambuc<li>The <a href="http://www.nist.gov/el/isd/ieee/ieee1588.cfm">Precision 638*0a6a1f1dSLionel SambucTime Protocol</a> (<abbr 639*0a6a1f1dSLionel Sambuctitle="Institute of Electrical and Electronics Engineers">IEEE</abbr> 1588) 640*0a6a1f1dSLionel Sambuccan achieve submicrosecond clock accuracy on a local area network.</li> 6412fe8fb19SBen Gras<li><a 64284d9c625SLionel Sambuchref="http://tools.ietf.org/html/rfc4833">Timezone 6432fe8fb19SBen GrasOptions for <abbr title="Dynamic Host Configuration Protocol">DHCP</abbr></a> 6442fe8fb19SBen Gras(Internet <abbr>RFC</abbr> 4833) 6452fe8fb19SBen Grasspecifies a <a 646*0a6a1f1dSLionel Sambuchref="https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol"><abbr>DHCP</abbr></a> 64784d9c625SLionel Sambucoption for a server to configure 6482fe8fb19SBen Grasa client's time zone and daylight saving settings automatically.</li> 649*0a6a1f1dSLionel Sambuc<li><a href="http://gauss.gge.unb.ca/GMT.UT.and.the.RGO.html">A Few Facts 650*0a6a1f1dSLionel SambucConcerning <abbr>GMT</abbr>, <abbr>UT</abbr>, and 6512fe8fb19SBen Grasthe <abbr title="Royal Greenwich Observatory">RGO</abbr></a> 6522fe8fb19SBen Grasanswers questions like "What is the 6532fe8fb19SBen Grasdifference between <abbr>GMT</abbr> and <abbr>UTC</abbr>?"</li> 6542fe8fb19SBen Gras<li><a 6552fe8fb19SBen Grashref="http://www.cv.nrao.edu/~rfisher/Ephemerides/times.html">Astronomical 6562fe8fb19SBen GrasTimes</a> explains more abstruse astronomical time scales like 6572fe8fb19SBen Gras<abbr title="Terrestrial Dynamic Time">TDT</abbr>, 6582fe8fb19SBen Gras<abbr title="Geocentric Coordinate Time">TCG</abbr>, and 6592fe8fb19SBen Gras<abbr title="Barycentric Dynamic Time">TDB</abbr>. 6602fe8fb19SBen Gras<a href="http://www.ucolick.org/~sla/leapsecs/timescales.html">Time 6612fe8fb19SBen GrasScales</a> goes into more detail, particularly for historical variants.</li> 662*0a6a1f1dSLionel Sambuc<li>The <a href="http://iau.org"><abbr 6632fe8fb19SBen Grastitle="International Astronomical Union">IAU</abbr></a>'s <a 664*0a6a1f1dSLionel Sambuchref="http://www.iausofa.org"><abbr 6652fe8fb19SBen Grastitle="Standards Of Fundamental Astronomy">SOFA</abbr></a> 666*0a6a1f1dSLionel Sambuccollection contains C and <a 667*0a6a1f1dSLionel Sambuchref="https://en.wikipedia.org/wiki/Fortran">Fortran</a> 6682fe8fb19SBen Grascode for converting among time scales like 6692fe8fb19SBen Gras<abbr title="International Atomic Time">TAI</abbr>, 6702fe8fb19SBen Gras<abbr>TDB</abbr>, <abbr>TDT</abbr> and 6712fe8fb19SBen Gras<abbr>UTC</abbr>.</li> 67284d9c625SLionel Sambuc<li><a href="http://www2.jpl.nasa.gov/basics/bsf2-3.php">Basics of 673*0a6a1f1dSLionel SambucSpace Flight – Reference Systems – Time Conventions</a> 6742fe8fb19SBen Grasbriefly explains interplanetary space flight timekeeping.</li> 6752fe8fb19SBen Gras<li><a 6762fe8fb19SBen Grashref="http://www.giss.nasa.gov/tools/mars24/help/notes.html">Technical 6772fe8fb19SBen GrasNotes on Mars Solar Time as Adopted by the Mars24 Sunclock</a> briefly 6782fe8fb19SBen Grasdescribes Mars Coordinated Time (<abbr 6792fe8fb19SBen Grastitle="Mars Coordinated Time">MTC</abbr>) and the 6802fe8fb19SBen Grasdiverse local time 6812fe8fb19SBen Grasscales used by each landed mission on Mars.</li> 682*0a6a1f1dSLionel Sambuc<li><a href="http://leapsecond.com">LeapSecond.com</a> is 6832fe8fb19SBen Grasdedicated not only to leap seconds but to precise time and frequency 6842fe8fb19SBen Grasin general. It covers the state of the art in amateur timekeeping, and 6852fe8fb19SBen Grashow the art has progressed over the past few decades.</li> 6862fe8fb19SBen Gras<li><a 687*0a6a1f1dSLionel Sambuchref="http://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html"><abbr 688*0a6a1f1dSLionel Sambuctitle="International Earth Rotation and Reference Systems Service">IERS</abbr> 68984d9c625SLionel SambucBulletins</a> contains official publications of the International 69084d9c625SLionel SambucEarth Rotation and Reference Systems Service, which decides 6912fe8fb19SBen Graswhen leap seconds occur.</li> 6922fe8fb19SBen Gras<li>The <a 693*0a6a1f1dSLionel Sambuchref="https://pairlist6.pair.net/mailman/listinfo/leapsecs">Leap 6942fe8fb19SBen GrasSecond Discussion List</a> covers <a 6952fe8fb19SBen Grashref="http://gauss.gge.unb.ca/papers.pdf/gpsworld.november99.pdf">McCarthy 6962fe8fb19SBen Grasand Klepczynski's proposal to discontinue leap seconds</a>, 6972fe8fb19SBen Grasdiscussed further in 6982fe8fb19SBen Gras<a href="http://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The 6992fe8fb19SBen Grasleap second: its history and possible future</a>. 700*0a6a1f1dSLionel Sambuc<a href="http://www.ucolick.org/~sla/leapsecs/"><abbr>UTC</abbr> 701*0a6a1f1dSLionel Sambucmight be redefined 70284d9c625SLionel Sambucwithout Leap Seconds</a> gives pointers on this 7032fe8fb19SBen Grascontentious issue.</li> 7042fe8fb19SBen Gras</ul> 7052fe8fb19SBen Gras<h2>Time notation</h2> 7062fe8fb19SBen Gras<ul> 707*0a6a1f1dSLionel Sambuc<li>The <a href="http://cldr.unicode.org">Unicode Common Locale Data 708*0a6a1f1dSLionel SambucRepository (<abbr>CLDR</abbr>) Project</a> has localizations for time 709*0a6a1f1dSLionel Sambuczone names, abbreviations, identifiers, and formats. For example, it 710*0a6a1f1dSLionel Sambuccontains French translations for "Eastern European Summer Time", 711*0a6a1f1dSLionel Sambuc"<abbr title="Eastern European Summer Time">EEST</abbr>", and 712*0a6a1f1dSLionel Sambuc"Bucharest". Its 713*0a6a1f1dSLionel Sambuc<a href="http://unicode.org/cldr/charts/by_type/index.html">by-type 714*0a6a1f1dSLionel Sambuccharts</a> show these values for many locales. Data values are available in 715*0a6a1f1dSLionel Sambucboth <abbr title="Locale Data Markup Language">LDML</abbr> 716*0a6a1f1dSLionel Sambuc(an <abbr>XML</abbr> format) and <abbr>JSON</abbr>. 7172fe8fb19SBen Gras<li> 71884d9c625SLionel Sambuc<a href="http://www.cl.cam.ac.uk/~mgk25/iso-time.html">A summary of 71984d9c625SLionel Sambucthe international standard date and time notation</a> is a good 7202fe8fb19SBen Grassummary of 7212fe8fb19SBen Gras<a 72284d9c625SLionel Sambuchref="http://www.iso.org/iso/catalogue_detail?csnumber=40874"><abbr 7232fe8fb19SBen Grastitle="International Organization for Standardization">ISO</abbr> 724*0a6a1f1dSLionel Sambuc8601:2004 – Data elements and interchange formats – Information 725*0a6a1f1dSLionel Sambucinterchange – Representation of dates and times</a>.</li> 7262fe8fb19SBen Gras<li> 7272fe8fb19SBen Gras<a href="http://www.w3.org/TR/xmlschema-2/#dateTime"><abbr>XML</abbr> 728*0a6a1f1dSLionel SambucSchema: Datatypes – dateTime</a> specifies a format inspired by 729*0a6a1f1dSLionel Sambuc<abbr>ISO</abbr> 8601 that is in common use in <abbr>XML</abbr> data.</li> 7302fe8fb19SBen Gras<li> 73184d9c625SLionel Sambuc<a href="http://tools.ietf.org/html/rfc5322">Internet 73284d9c625SLionel SambucMessage Format</a> (Internet <abbr>RFC</abbr> 5322) §3.3 7332fe8fb19SBen Grasspecifies the time notation used in email and <a 734*0a6a1f1dSLionel Sambuchref="https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol"><abbr>HTTP</abbr></a> 7352fe8fb19SBen Grasheaders.</li> 7362fe8fb19SBen Gras<li> 73784d9c625SLionel Sambuc<a href="http://tools.ietf.org/html/rfc3339">Date and Time 7382fe8fb19SBen Grason the Internet: Timestamps</a> (Internet <abbr>RFC</abbr> 3339) 7392fe8fb19SBen Grasspecifies an <abbr>ISO</abbr> 8601 7402fe8fb19SBen Grasprofile for use in new Internet 7412fe8fb19SBen Grasprotocols.</li> 7422fe8fb19SBen Gras<li> 7432fe8fb19SBen Gras<a href="http://www.hackcraft.net/web/datetime/">Date & Time 7442fe8fb19SBen GrasFormats on the Web</a> surveys web- and Internet-oriented date and time 7452fe8fb19SBen Grasformats.</li> 7462fe8fb19SBen Gras<li> 7472fe8fb19SBen Gras<a href="http://exit109.com/~ghealton/y2k/yrexamples.html">The 7482fe8fb19SBen GrasBest of Dates, the Worst of Dates</a> covers many problems encountered 7492fe8fb19SBen Grasby software developers when handling dates and time stamps.</li> 7502fe8fb19SBen Gras<li>Alphabetic time zone abbreviations should not be used as unique 7512fe8fb19SBen Grasidentifiers for <abbr>UTC</abbr> offsets as they are ambiguous in 752*0a6a1f1dSLionel Sambucpractice. For example, in English-speaking North America 753*0a6a1f1dSLionel Sambuc"<abbr>CST</abbr>" denotes 6 hours behind <abbr>UTC</abbr>, 754*0a6a1f1dSLionel Sambucbut in China it denotes 8 hours ahead of <abbr>UTC</abbr>, 755*0a6a1f1dSLionel Sambucand French-speaking North Americans prefer 756*0a6a1f1dSLionel Sambuc"<abbr title="Heure Normale du Centre">HNC</abbr>" to 757*0a6a1f1dSLionel Sambuc"<abbr>CST</abbr>". For <abbr>POSIX</abbr> the <code><abbr>tz</abbr></code> 7582fe8fb19SBen Grasdatabase contains English abbreviations for all time stamps but in 7592fe8fb19SBen Grasmany cases these are merely inventions of the database 7602fe8fb19SBen Grasmaintainers.</li> 7612fe8fb19SBen Gras<li>Numeric time zone abbreviations typically count hours east of 762*0a6a1f1dSLionel Sambuc<abbr>UTC</abbr>, e.g., +09 for Japan and 763*0a6a1f1dSLionel Sambuc−10 for Hawaii. However, the <abbr>POSIX</abbr> 764*0a6a1f1dSLionel Sambuc<code><abbr>TZ</abbr></code> environment variable uses the opposite convention. 765*0a6a1f1dSLionel SambucFor example, one might use <code><abbr>TZ</abbr>="<abbr 766*0a6a1f1dSLionel Sambuctitle="Japan Standard Time">JST</abbr>-9"</code> and 767*0a6a1f1dSLionel Sambuc<code><abbr>TZ</abbr>="<abbr title="Hawaii Standard Time">HST</abbr>10"</code> 768*0a6a1f1dSLionel Sambucfor Japan and Hawaii, respectively. If the 769*0a6a1f1dSLionel Sambuc<code><abbr>tz</abbr></code> database is available, it is usually better to use 770*0a6a1f1dSLionel Sambucsettings like <code><abbr>TZ</abbr>="Asia/Tokyo"</code> and 771*0a6a1f1dSLionel Sambuc<code><abbr>TZ</abbr>="Pacific/Honolulu"</code> instead, as this should avoid 7722fe8fb19SBen Grasconfusion, handle old time stamps better, and insulate you better from 7732fe8fb19SBen Grasany future changes to the rules. One should never set 774*0a6a1f1dSLionel Sambuc<abbr>POSIX</abbr> <code><abbr>TZ</abbr></code> to a value like 7752fe8fb19SBen Gras<code>"GMT-9"</code>, though, since this would falsely claim that 7762fe8fb19SBen Graslocal time is nine hours ahead of <abbr>UTC</abbr> and the time zone 7772fe8fb19SBen Grasis called "<abbr>GMT</abbr>".</li> 7782fe8fb19SBen Gras</ul> 779*0a6a1f1dSLionel Sambuc<h2>See also</h2> 7802fe8fb19SBen Gras<ul> 7812fe8fb19SBen Gras<li><a href="tz-art.htm">Time and the Arts</a></li> 7822fe8fb19SBen Gras</ul> 78384d9c625SLionel Sambuc<hr> 78484d9c625SLionel Sambuc<address> 785*0a6a1f1dSLionel SambucThis web page is in the public domain, so clarified as of 78684d9c625SLionel Sambuc2009-05-17 by Arthur David Olson. 78784d9c625SLionel Sambuc<br> 78884d9c625SLionel SambucPlease send corrections to this web page to the 78984d9c625SLionel Sambuc<a href="mailto:tz@iana.org">time zone mailing list</a>. 79084d9c625SLionel Sambuc</address> 7912fe8fb19SBen Gras</body> 7922fe8fb19SBen Gras</html> 793