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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 328495 $ -->
<refentry xml:id="function.easter-date" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>easter_date</refname>
<refpurpose>Get Unix timestamp for midnight on Easter of a given year</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>int</type><methodname>easter_date</methodname>
<methodparam choice="opt"><type>int</type><parameter>year</parameter></methodparam>
</methodsynopsis>
<para>
Returns the Unix timestamp corresponding to midnight on Easter of
the given year.
</para>
<warning>
<para>
This function will generate a warning if the year is outside
of the range for Unix timestamps (i.e. before 1970 or after 2037).
</para>
</warning>
<para>
The date of Easter Day was defined by the Council of Nicaea in
AD325 as the Sunday after the first full moon which falls on or
after the Spring Equinox. The Equinox is assumed to always fall
on 21st March, so the calculation reduces to determining the date
of the full moon and the date of the following Sunday. The
algorithm used here was introduced around the year 532 by
Dionysius Exiguus. Under the Julian Calendar (for years before
1753) a simple 19-year cycle is used to track the phases of the
Moon. Under the Gregorian Calendar (for years after 1753 -
devised by Clavius and Lilius, and introduced by Pope Gregory
XIII in October 1582, and into Britain and its then colonies in
September 1752) two correction factors are added to make the
cycle more accurate.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>year</parameter></term>
<listitem>
<para>
The year as a number between 1970 an 2037
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
The easter date as a unix timestamp.
</para>
</refsect1>
<refsect1 role="changelog">
&reftitle.changelog;
<para>
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>&Version;</entry>
<entry>&Description;</entry>
</row>
</thead>
<tbody>
<row>
<entry>4.3.0</entry>
<entry>
The <parameter>year</parameter> parameter is optional and defaults
to the current year according to the local time if omitted.
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title><function>easter_date</function> example</title>
<programlisting role="php">
<![CDATA[
<?php
echo date("M-d-Y", easter_date(1999)); // Apr-04-1999
echo date("M-d-Y", easter_date(2000)); // Apr-23-2000
echo date("M-d-Y", easter_date(2001)); // Apr-15-2001
?>
]]>
</programlisting>
</example>
</para>
</refsect1>
<refsect1 role="notes">
&reftitle.notes;
<note>
<para>
<function>easter_date</function> relies on your system's C library time
functions, rather than using PHP's internal date and time functions. As a
consequence, <function>easter_date</function> uses the
<literal>TZ</literal> environment variable to determine the time zone it
should operate in, rather than using PHP's
<link linkend="ini.date.timezone">default time zone</link>, which may
result in unexpected behaviour when using this function in conjunction
with other date functions in PHP.
</para>
<para>
As a workaround, you can use the <function>easter_days</function> with
<classname>DateTime</classname> and <classname>DateInterval</classname> to
calculate the start of Easter in your PHP time zone as follows:
</para>
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
function get_easter_datetime($year) {
$base = new DateTime("$year-03-21");
$days = easter_days($year);
return $base->add(new DateInterval("P{$days}D"));
}
foreach (range(2012, 2015) as $year) {
printf("Easter in %d is on %s\n",
$year,
get_easter_datetime($year)->format('F j'));
}
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
Easter in 2012 is on April 8
Easter in 2013 is on March 31
Easter in 2014 is on April 20
Easter in 2015 is on April 5
]]>
</screen>
</informalexample>
</note>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member>
<function>easter_days</function> for calculating Easter
before 1970 or after 2037
</member>
</simplelist>
</para>
</refsect1>
</refentry>
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