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<?xml version="1.0" encoding="US-ASCII"?>
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<title>Sources for Time Zone and Daylight Saving Time Data</title>
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content="Sources of information about time zones and daylight saving time" />
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<h1>Sources for Time Zone and Daylight Saving Time Data</h1>
<address>
@(#)tz-link.htm 7.30
</address>
<p>
Please send corrections to this web page to the
<a href="mailto:tz@elsie.nci.nih.gov">time zone mailing list</a>.
</p>
<h2>The <samp>tz</samp> database</h2>
<p>
The public-domain time zone database contains code and data
that represent the history of local time
for many representative locations around the globe.
It is updated periodically to reflect changes made by political bodies
to UTC offsets and daylight-saving rules.
This database (often called <samp>tz</samp> or <samp>zoneinfo</samp>)
is used by several implementations,
including
<a href="http://www.linux.org/">GNU/Linux</a>,
<a href="http://www.freebsd.org/">FreeBSD</a>,
<a href="http://www.netbsd.org/">NetBSD</a>,
<a href="http://www.openbsd.org/">OpenBSD</a>,
<a href="http://www.delorie.com/djgpp/">DJGPP</a>,
<a href="http://unix.hp.com/operating/">HP-UX</a>,
<a href="http://www.sgi.com/developers/technology/irix.html">IRIX</a>,
<a href="http://www.sco.com/products/openserver/">SCO OpenServer</a>,
<a href="http://www.sun.com/solaris/">Solaris</a>, and
<a href="http://www.sco.com/unixware/">UnixWare</a>.
In the <samp>tz</samp> database's
<a href="ftp://elsie.nci.nih.gov/pub/">FTP distribution</a>,
the code is in the file <samp>tzcode<var>C</var>.tar.gz</samp>,
where <samp><var>C</var></samp> is the code's version;
similarly, the data are in <samp>tzdata<var>D</var>.tar.gz</samp>,
where <samp><var>D</var></samp> is the data's version.
The code lets you compile the text data into time zone files, one for
each location. It also lets you read a compiled time zone file and
interpret time stamps for that location.</p>
<p>
The data are by no means authoritative. If you find errors, please
send changes to the <a href="mailto:tz@elsie.nci.nih.gov">time zone
mailing list</a>. You can also <a
href="mailto:tz-request@elsie.nci.nih.gov">subscribe</a> to the
mailing list, or retrieve the <a
href="ftp://elsie.nci.nih.gov/pub/tzarchive.gz">archive of old
messages</a> (in <a href="http://www.gzip.org/">gzip</a> compressed
format).</p>
<p>
The Web has several other sources for time zone and daylight saving time data.
Here are some recent links that may be of interest.
</p>
<h2>Web pages using recent versions of the <samp>tz</samp> database</h2>
<ul>
<li><a href="http://www.bsdi.com/date/">Date and Time Gateway</a> is a
text-based point-and-click interface to tables of current time
throughout the world.</li>
<li><a href="http://sandbox.xerox.com/stewart/tzconvert.cgi">CGI/1.0
URL Timezone Converter</a> is a similar interface, with source code
written in <a href="http://www.perl.org/">Perl</a>, using what Paul
Stewart calls the "20-line hack no one will let me forget".</li>
<li>Fancier web interfaces, roughly in ascending order of complexity, include:
<ul>
<li><a href="http://www.hilink.com.au/times/">Local Times Around the
World</a></li>
<li><a href="http://www.convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current Time in 1000 Places</a></li>
<li><a href="http://timezoneconverter.com/">Time Zone Converter</a></li>
</ul></li>
<li><a href="http://www.tick2tock.com/cgi-bin/TZConverter">Tick2Tock
time zone converter</a> is a multilingual interface.</li>
<li><a href="http://www.holidayfestival.com/">The Worldwide Holiday
& Festival Site</a> lists DST-related clock changes along with
holidays.</li>
<li><a href="http://www.timeanddate.com/worldclock/">The World Clock</a>
is a web interface to a time zone database derived from
<samp>tz</samp>'s.</li>
</ul>
<h2>Other time zone file readers</h2>
<ul>
<li>The <a href="http://www.gnu.org/software/libc/">GNU C Library</a>
has an independent, thread-safe implementation of
a time zone file reader that is compatible with <samp>tz</samp>.
This library is freely available under the
<a href="http://www.gnu.org/copyleft/lesser.html">
GNU Lesser General Public License (LGPL)</a>,
and is widely used in GNU/Linux systems.</li>
<li><a href="http://www.bmsi.com/java/#TZ">ZoneInfo.java</a>
is a time zone file reader written in Java.
It is freely available under the GNU LGPL.</li>
</ul>
<h2>Other <samp>tz</samp>-based time zone conversion software</h2>
<ul>
<li><a
href="http://www1.tip.nl/~t876506/AboutTimeZonesHC.html">HyperCard
time zones calculator</a> is a HyperCard stack.</li>
<li><a
href="http://timezone50.homepage.com/">Time Zone Converter</a> is a
Microsoft Windows 95/98/NT4 program.</li>
</ul>
<h2>Other time zone databases</h2>
<ul>
<li><a href="http://www.astro.ch/cgi-bin/atlw3/aq.cgi?lang=e">Astrodienst
- Atlas Query</a> is Astrodienst's Web version of Shanks's
excellent time zone history atlases published in both <a
href="http://astrocom.com/software/pcatlas.html">computer</a> and <a
href="http://astrocom.com/books/xrefa.htm#SHANKS">book</a> form by <a
href="http://astrocom.com/">Astro Communications Services</a>.</li>
<li><a href="http://worldtime.com/">WORLDTIME: interactive atlas,
time info, public holidays</a>
contains information on local time, sunrise and sunset,
and public holidays in several hundred cities around the world.</li>
<li><a href="http://tycho.usno.navy.mil/tzones.html">World Time Zones</a>
contains data from the Time Service Department of the US Naval Observatory
(USNO), used as the source
for the <samp>usno*</samp> files in the <samp>tz</samp> distribution.</li>
<li>The <a href="http://www.iata.org/">International
Air Transport Association</a>
publishes the <a href="http://www.iata.org/sked/ssim.htm">Standard
Schedules Information Manual</a>,
which gives current time zone rules for
all the airports served by commercial aviation.</li>
</ul>
<h2>Maps</h2>
<ul>
<li>The <a href="http://www.odci.gov/">United States Central
Intelligence Agency (CIA)</a> publishes a <a
href="http://www.odci.gov/cia/publications/factbook/reference/Low%20res%20PDF/low802700.pdf">time
zone map</a>; the
<a href="http://www.lib.utexas.edu/Libs/PCL/Map_collection/world_maps.html">
Perry-Castañeda Library Map Collection</a>
of the University of Texas at Austin has copies of
recent editions.
The pictorial quality is good,
but the maps do not indicate summer time,
and parts of the data are a few years out of date.</li>
<li><a href="http://worldtimezone.com/">World timezones map with
current time</a>
has several fancy time zone maps; it covers Russia particularly well.
The maps' pictorial quality is not quite as good as the CIA's
but the maps are more up to date.</li>
<li><a href="http://www.worldtimeserver.com/">World Time Server</a>
has a separate little outline map for each region of each country that
currently observes a different time.</li>
</ul>
<h2>Time zone boundaries</h2>
<ul>
<li>Manifold.net's <a
href="http://www.manifold.net/download/freemaps.html">Free Maps and
GIS Data</a> includes a Manifold-format map of world time zone
boundaries distributed under the <a
href="http://www.gnu.org/copyleft/gpl.html">GNU General Public License
(GPL)</a>. The GeoCommunity's <a
href="http://software.geocomm.com/data/intl_timezones.html">International
Time Zones</a> publishes the same data in other formats.</li>
<li>The US Geological Survey's National Atlas of the United States
publishes the <a href="http://www.nationalatlas.gov/timeznm.html">Time
Zones of the United States</a> in the public domain.</li>
<li>The GeoCommunity lists several commercial sources for <a
href="http://spatialnews.geocomm.com/features/timezones/">International
Time Zones and Time Zone Data</a>.</li>
</ul>
<h2>Daylight saving time concepts and history</h2>
<ul>
<li><a href="http://webexhibits.com/daylightsaving/">About Daylight
Saving Time - History, rationale, laws and dates</a>
is a good overall history of DST.</li>
<li><a href="http://toi.iriti.cnr.it/">The
Time of Internet</a>
contains good descriptions of Time Zones and daylight saving time,
with diagrams.
The time zone map is out of date, however.</li>
<li>A few countries have well-documented histories of legal time.
<dl>
<dt>Australia</dt>
<dd>The Community Relations Division of the NSW Attorney General's
Department maintains a history of <a
href="http://www.lawlink.nsw.gov.au/crd.nsf/pages/time2">daylight
saving in New South Wales</a>.</dd>
<dt>Brazil</dt>
<dd>The Time Service Department of the National Observatory
records <a href="http://pcdsh01.on.br/DecHV.html"
hreflang="pt-BR">Brazil's daylight saving time decrees (in
Portuguese)</a>.</dd>
<dt>Germany</dt>
<dd>The National Institute for Science and Technology maintains the <a
href="http://www.ptb.de/english/org/4/43/432/lega.htm">Realisation of
Legal Time in Germany</a>.</dd>
<dt>Israel</dt>
<dd>The Ministry of Interior periodically issues <a
href="ftp://ftp.huji.ac.il/pub/tz/announcements"
hreflang="he">announcements (in Hebrew)</a>.</dd>
<dt>Mexico</dt>
<dd>The Investigation and Analysis Service of the Mexican Library of
Congress has published a <a
href="http://www.cddhcu.gob.mx/bibliot/publica/inveyana/polisoc/horver/"
hreflang="es">history of Mexican local time (in Spanish)</a>.</dd>
<dt>United Kingdom</dt>
<dd><a
href="http://student.cusu.cam.ac.uk/~jsm28/british-time/">History of
legal time in Britain</a> is an excellent discussion for the country
with perhaps the best-documented history of clock adjustments.</dd>
</dl></li>
</ul>
<h2>Precision timekeeping</h2>
<ul>
<li><a
href="http://literature.agilent.com/litwebbin/purl.cgi?org_id=tmo&pub_id=5965-7984E">The
Science of Timekeeping</a> is an excellent and thorough introduction
to the theory and practice of precision timekeeping.</li>
<li><a href="http://www.eecis.udel.edu/~ntp/">Time Server</a> discusses
the Network Time Protocol (NTP), used to synchronize clocks of
Internet hosts.</li>
<li><a href="http://ecco.bsee.swin.edu.au/chronos/GMT-explained.html">A
Few Facts Concerning GMT, UT, and the RGO</a>
answers questions like "What is the difference between GMT and UTC?"</li>
<li><a
href="http://sadira.gb.nrao.edu/~rfisher/Ephemerides/times.html">Astronomical
Times</a> explains more abstruse astronomical time scales like TT, TCG,
and TDB.</li>
<li><a href="http://www.jpl.nasa.gov/basics/bsf2-3.htm">Basics of
Space Flight - Reference Systems - Time Conventions</a>
briefly explains interplanetary space flight timekeeping.</li>
<li><a href="http://hpiers.obspm.fr/webiers/results/bul/README.html">Bulletins
of IERS</a> contains official publications of the
International Earth Rotation Service, the committee that decides
when leap seconds occur.</li>
<li>The <a
href="http://clockdev.usno.navy.mil/archives/leapsecs.html">Leap
Second Discussion List</a> covers <a
href="http://clockdev.usno.navy.mil/cgi-bin/wa.exe?A3=ind00&L=leapsecs&P=28537&E=2&B=------_=_NextPart_000_01C0781C.F015C5B0&N=GPS-Nov99_Innov.pdf&T=application/octet-stream">McCarthy
and Klepczynski's proposal to remove leap seconds</a>
(which requires discussion list membership to read).
This proposal is being studied by the URSI Commission J <a
href="http://space.mit.edu/URSI/leapsecond.html">Working Group on the
Leap Second</a>, and the <a href="http://www.iau.org/">IAU</a>
has plans to report on this proposal by 2003.</li>
</ul>
<h2>Time notation</h2>
<ul>
<li>
<a href="http://www.cl.cam.ac.uk/~mgk25/iso-time.html">A Summary of
the International Standard Date and Time Notation</a> is a good
summary of <a href="http://www.iso.ch/markete/8601.pdf">ISO
8601:1988 - Data elements and interchange formats - Information interchange
- Representation of dates and times</a>.</li>
</ul>
<h2>Related indexes</h2>
<ul>
<li><a href="http://dmoz.org/Reference/Time/">Open Directory -
Reference: Time</a></li>
<li><a href="tz-art.htm">Time and the Arts</a></li>
<li><a href="http://dir.yahoo.com/Science/Measurements_and_Units/Time/Time_Zones/">Yahoo! - Science:Measurements and Units:Time:Time Zones</a></li>
</ul>
</body>
</html>
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