|
|
|
|
Bookmark this on Delicious
Share on Facebook
 Slashdot It!
Digg  jdtounix
Convert Julian Day to Unix timestamp
(PHP 4, PHP 5)
Code Examples / Notes » jdtounix27-jan-2005 02:50
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!! seb
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. pipian
Remember that UNIX timestamps indicate a number of seconds from midnight of January 1, 1970 on the Gregorian calendar, not the Julian Calendar.
erelsgl dot nospam
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 ?> fabio
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 hrabi
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 \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 |
