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jdtounix — Konvertiert Julianisches Datum in Unix-Timestamp
Diese Funktion liefert einen Unix-Timestamp (in Sekunden seit dem 1.1.1970) zurück, der dem in jday übergebenen Julianischen Datum entspricht. Liegt jday außerhalb des darstellbaren Zeitbereichs (Gregorianische Jahre von 1970 bis 2037 bzw. 2440588 <= jday <= 2465342 ), so wird FALSE zurückgegeben.
Ein Julianischer Tag zwischen 2440588 and 2465342.
Der Unix-Timestamp für den Anfang des gegebenen Julianischen Tages.
Beware, jd here is not (astronomical or geocentric) Julian Day (JD), but Chronological Julian Day (CJD)! When JD start at noon of UTC time (12:00 UTC), CJD start at midnight at *local* time! Or considering head "Chronlogical Julian Day/Date" at "http://www.decimaltime.hynes.net/dates.html", when day localy start (it should be at sunset for instance).
try this...
<?php
define("UJD", 2440587.5);
define("SEC4DAY", 86400);
function u2j($tm) {
return $tm / SEC4DAY + UJD;
}
function mmd($txt, $str_time) {
$t = strtotime($str_time);
$j = unixtojd($t);
$j_fabio = u2j($t);
$s = strftime('%D %T %Z', $t);
printf("${txt} => %s, CJD: %s, JD: %s<br>\n", $s, $j, $j_fabio);
}
$xt = strtotime("1.1.1970 0:00.00 GMT");
$slb = "-1 day 23:30"; // let CJD be N
$sla = "0:30.00"; // should be N+1
$slm = "0:00"; // should be N+1
$sgmt = "0:00.00 GMT"; // don't forget to observe JD.
mmd("local before", $slb);
mmd("local after", $sla);
mmd("local midnight", $slm);
mmd("GMT midnight", $sgmt);
?>
I got this (you see, JD havn't change day, because UTC noon is far away):
local before => 03/28/07 23:30:00 CEST, CJD: 2454188, JD: 2454188.39583
local after => 03/29/07 00:30:00 CEST, CJD: 2454189, JD: 2454188.4375
local midnight => 03/29/07 00:00:00 CEST, CJD: 2454189, JD: 2454188.41667
GMT midnight => 03/29/07 02:00:00 CEST, CJD: 2454189, JD: 2454188.5
Just to clarify the differences between the different methods to convert a date to a timestamp.
Suppose:
<?php
$x = JDToUnix(GregorianToJD(9,23,2006));
$y = strtotime('2006-09-23');
$z = (GregorianToJD(9,23,2006) - 2440587.5) * 86400;
?>
Then, on a machine whoze timezone is GMT-0400, we get the following results:
<?php
$x === 1158969600;
$y === 1158984000; // $x + 4 hours
$z === 1159012800; // $x + 12 hours
?>
If you need an easy way to convert a decimal julian day to an unix timestamp you can use:
$unixTimeStamp = ($julianDay - 2440587.5) * 86400;
2440587.5 is the julian day at 1/1/1970 0:00 UTC
86400 is the number of seconds in a day
Warning: the calender functions involving julian day operations seem to ignore the decimal part of the julian day count.
This means that the returned date is wrong 50% of the time, since a julian day starts at decimal .5 . Take care!!
Remember that unixtojd() assumes your timestamp is in GMT, but jdtounix() returns a timestamp in localtime.
This fooled me a few times.
So if you have:
$timestamp1 = time();
$timestamp2 = jdtounix(unixtojd($timestamp1));
Unless your localtime is the same as GMT, $timestamp1 will not equal $timestamp2.
Remember that UNIX timestamps indicate a number of seconds from midnight of January 1, 1970 on the Gregorian calendar, not the Julian Calendar.
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