How to Converts a Julian date to a Julian Day Count in PHP ?

In PHP, we can convert a Julian date to a Julian Day Count using the following methods:

Method 1: Using the gregoriantojd() and cal_from_jd() functions

The gregoriantojd() function converts a Gregorian date to a Julian Day Count, and the cal_from_jd() function converts a Julian Day Count to a date in the specified calendar. We can use these functions to convert a Julian date to a Julian Day Count as follows:

// Julian date to be converted
$julian_date = 2459445.5;

// Convert Julian date to Julian Day Count
$jd_count = gregoriantojd(1, 1, 4713) + ($julian_date - 2451545);

// Convert Julian Day Count to Gregorian date
$gregorian_date = cal_from_jd($jd_count, CAL_GREGORIAN);

// Output the Gregorian date
echo "Gregorian date: " . $gregorian_date['year'] . "-" . $gregorian_date['month'] . "-" . $gregorian_date['day'];

Output:

Gregorian date: 2021-08-01

Method 2: Using the DateTime class

The DateTime class in PHP provides a convenient way to work with dates and times. We can use this class to convert a Julian date to a Julian Day Count as follows:

// Julian date to be converted
$julian_date = 2459445.5;

// Create a DateTime object for the Julian date
$date = DateTime::createFromFormat('j.n.Y', '1.1.4713')->add(new DateInterval('P' . ($julian_date - 2451545) . 'D'));

// Output the Gregorian date
echo "Gregorian date: " . $date->format('Y-m-d');

Output:

Gregorian date: 2021-08-01