jdtogregorian

(PHP 4, PHP 5, PHP 7)

jdtogregorian — Converts Julian Day Count to Gregorian date

Description

string jdtogregorian ( int $julianday )

Converts Julian Day Count to a string containing the Gregorian date in the format of "month/day/year".

Parameters

julianday: A julian day number as integer

Return Values

The gregorian date as a string in the form "month/day/year"

User Contributed Notes

httpwebwitch

11 years ago


JD days may have decimal fractions which correspond to the time of day. The Julian day begins at noon, and the decimal fraction measures fractional days until the beginning of the next day at noon.

For instance, Julian Day 2453179.00000 is June 22, 2004, at 12:00pm (noon). 

One hour later, it's 2453179.04167
At 2453179.20833 I'll have dinner, and
at 2453179.45833, it's time for the evening news.
After a good night of sleep, my alarm will go off at 2453179.83333, 
then at noon on June 23, a new Julian Day begins at 2453180.

To use these functions with fractional days, strip the fractional part with floor(), and apply the function to the integer part. 

Then add 12 hours, bringing you to noon of that day. That is the actual time returned by JDToGregorian().

Then add the fractional part of the day, by multiplying the decimal part of the Julian Day by (24*60*60) seconds. This may take you forward or backward to a different Gregorian calendar date.

swiles at ddbc dot edu dot tw

7 years ago


The php gregoriantojd() and jdtogregorian() functions, in addition to the limitations noted by httpwebwitch, does not take account of the 'Astronomical' system of reckoning - i.e. using a year zero, instead of going directly from 1BCE to 1CE, as with the Christian Anno Domini system.

These functions can be used to wrap the php built-ins to return ISO 8601 compliant dates:

<?php
function ISO8601toJD($ceDate) {
    list($day, $month, $year) = array_map('strrev',explode('-', strrev($ceDate), 3));
    if ($year <= 0) $year--;
    return gregoriantojd($month, $day, $year);
}

function JDtoISO8601($JD) {
    if ($JD <= 1721425) $JD += 365;
    list($month, $day, $year) = explode('/', jdtogregorian($JD));
    return sprintf('%+05d-%02d-%02d', $year, $month, $day);
}
?>

uni_fl4r3 at t hotmail dot com

12 years ago


I have made a slight modification to treebe's jd to greg function, this one will transform a unix timestamp to Gregorian day/month/year format...



<?php

function unix_to_greg($unix_timestamp) {

    $julian = floor(((($unix_timestamp / "60") / "60") / "24") + "2440588");

    $julian = $julian - 1721119;

    $calc1 = 4 * $julian - 1;

    $year = floor($calc1 / 146097);

    $julian = floor($calc1 - 146097 * $year);

    $day = floor($julian / 4);

    $calc2 = 4 * $day + 3;

    $julian = floor($calc2 / 1461);

    $day = $calc2 - 1461 * $julian;

    $day = floor(($day + 4) / 4);

    $calc3 = 5 * $day - 3;

    $month = floor($calc3 / 153);

    $day = $calc3 - 153 * $month;

    $day = floor(($day + 5) / 5);

    $year = 100 * $year + $julian;

    

    if ($month < 10)

    {

        $month = $month + 3;

    }else{

        $month = $month - 9;

        $year = $year + 1;

    }

    return "$day.$month.$year";

}

?>

treebe