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Convert Unix timestamp to Julian Day
(PHP 4, PHP 5)
Code Examples / Notes » unixtojdwarhog
Well, that's neither a bug, nor an interesting quirk.. The explanation is quite simple: The Integer containing a julian date (jd) only stores the date, not the time. When you convert a unix-timestamp, which stores also the time, into a jd, the time-information won't be transferred into the jd. When converting back the jd into a unix-timestamp, you'll get a timestamp for the specific day at 2 o'clock am. ( 02:00:00 ) Sample: Timestamp: 1121206013 JD: 2453565 Timestamp from JD: 1121212800 Original Timestamp "d.m.y H:i:s": 13.07.2005 00:06:53 Timstamp from JD "d.m.y H:i:s": 13.07.2005 02:00:00 greetz hrabi
This is unusable. Julian Day start at noon, not midnight. It's better to use Fabio solution (however there is a lurk problem with leap second). <?php function mmd($txt, $str_time) { $t = strtotime($str_time); $j = unixtojd($t); $s = gmstrftime('%D %T %Z', $t); $j_fabio = $t / 86400 + 2440587.5; printf("${txt} => (%s) %s, %s U, %s J, or %s J \n", $str_time, $s, $t, $j, $j_fabio); } //$xt = strtotime("1.1.1970 15:00.00 GMT"); $sam = "9.10.1995 02:00.01 GMT"; $spm = "9.10.1995 22:00.01 GMT"; // unixtojd for $spm returns 2450000 (OK), but for $sam returns 2450000 too! (it is wrong). mmd("am", $sam); // should be 2449999 (+ 0.58334) mmd("pm", $spm); // should be 2450000 (+ 0.41668) ?> reference unix time, and UTC, TAI, ntp, ... problems: http://en.wikipedia.org/wiki/Unix_time Julian Date Converter: http://aa.usno.navy.mil/data/docs/JulianDate.html history overview: http://parris.josh.com.au/humour/work/17Nov1858.shtml pipian
Remember that UNIX timestamps indicate a number of seconds from midnight of January 1, 1970 on the Gregorian calendar, not the Julian Calendar.
11-aug-2006 03:22
Its clearly stated that this function returns the Julian Day, not Julian Day + time. If you want the time with it you will have to do something like: $t=time(); $jd=unixtojd($t)+($t%60*60*24)/60*60*24; mike
Interesting quirk ... maybe bug. If you use today = unixtojd(time()) then use jdtounix(today) the result is one day short of today. fabio
If you need an easy way to convert an unix timestamp to a decimal julian day you can use: $julianDay = $unixTimeStamp / 86400 + 2440587.5; 86400 is the number of seconds in a day; 2440587.5 is the julian day at 1/1/1970 0:00 UTC. johnston
Also note that epoch is in UTC time (epoch is a specific point in time - epoch is not different for every time zone), so be aware of timezone complexities.
hrabi
according to http://www.decimaltime.hynes.net/dates.html#jd and reading "X. Calendar Functions" on this side, it seems that php "jd" is precisely mean as "Chronological Julian Day" (should it be named cjd, and primarily strictly mentioned - isn't it?), used for covnersion between calendar systems. Than it's ok (but Incomplete manual is strongly confusing here IMHO). Even that, cJD is adjusted to a local time, so... I am rather babeled now, so nothing else :-). |
