Julian days begin at noon, while the days of the Gregorian and Julian calendars are usually thought of as beginning at midnight. For the Gregorian and Julian calendars, the function behaves as if the conversion were performed at noon.
(PHP 4 >= 4.1.0, PHP 5, PHP 7, PHP 8)
cal_to_jd — Converts from a supported calendar to Julian Day Count
cal_to_jd() calculates the Julian day count
for a date in the specified calendar.
Supported calendars are
CAL_GREGORIAN,
CAL_JULIAN,
CAL_JEWISH and
CAL_FRENCH.
calendar
Calendar to convert from, one of
CAL_GREGORIAN,
CAL_JULIAN,
CAL_JEWISH or
CAL_FRENCH.
month
The month as a number, the valid range depends
on the calendar
day
The day as a number, the valid range depends
on the calendar
year
The year as a number, the valid range depends
on the calendar
A Julian Day number.
Julian days begin at noon, while the days of the Gregorian and Julian calendars are usually thought of as beginning at midnight. For the Gregorian and Julian calendars, the function behaves as if the conversion were performed at noon.The earliest supported date in the Julian calendar is January 2, 4713 BC. The corresponding Julian day count is 1. PHP treats -4713 as equal to 4713 BC, and does not allow the year 0; this practice is different than the custom of astronomers, who treat -4712 as equal to 4713 BC.