Recipe 3.16 Using Non-Gregorian Calendars
3.16.1 Problem
You want to use a non-Gregorian
calendar, such as a Julian, Jewish, or French Republican
calendar.
3.16.2 Solution
PHP's calendar
extension provides conversion functions for working with the Julian
calendar, as well as the French Republican and Jewish calendars. To
use these functions, the calendar extension must be loaded.
These functions use the Julian day count (which is different than the
Julian calendar) as their intermediate format to move information
between them.
The two functions jdtogregorian(
)
and
gregoriantojd( ) convert between Julian days and
the familiar Gregorian calendar:
$jd = gregoriantojd(3,9,1876); // March 9, 1876; $jd = 2406323
$gregorian = jdtogregorian($jd); // $gregorian = 3/9/1876
The valid range for the Gregorian calendar is 4714 BCE to 9999 CE.
3.16.3 Discussion
To convert between Julian days and the Julian calendar,
use jdtojulian( ) and juliantojd( ):
// February 29, 1900 (not a Gregorian leap year)
$jd = juliantojd(2,29,1900); // $jd = 2415092
$julian = jdtojulian($jd); // $julian = 2/29/1900
$gregorian = jdtogregorian($jd); // $gregorian = 3/13/1900
The valid range for the Julian calendar is 4713 BCE to 9999 CE, but
since it was created in 46 BCE, you run the risk of annoying Julian
calendar purists if you use it for dates before that.
To convert between Julian days and the French Republican
calendar, use jdtofrench(
)
and
frenchtojd( ):
$jd = frenchtojd(8,13,11); // 13 floréal XI; $jd = 2379714
$french = jdtofrench($jd); // $french = 8/13/11
$gregorian = jdtofregorian($jd); // $gregorian = 5/3/1803; sale of Louisiana to U.S.
The valid range for the French Republican calendar is September 1792
to September 1806, which is small, but since the calendar was only in
use from October 1793 to January 1806, it's
comprehensive enough.
To convert between Julian days and the Jewish calendar, use jdtojewish(
)
and
jewishtojd( ):
$jd = JewishToJD(6,14,5761); // Adar 14, 5761; $jd = 2451978
$jewish = JDToJewish($jd); // $jewish = 6/14/5761
$gregorian = JDToGregorian($jd); // $gregorian = 3/9/2001
The valid range for the Jewish calendar starts with 3761 BCE (year 1
on the Jewish calendar).
3.16.4 See Also
Documentation for the calendar functions at
http://www.php.net/calendar; the history of the
Gregorian calendar is explained at
http://scienceworld.wolfram.com/astronomy/GregorianCalendar.html.
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