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 — 从支持的历法转换为儒略日数
$calendar,$month,$day,$year
cal_to_jd() 计算指定 calendar 中某个日期的儒略日数。支持的历法有
CAL_GREGORIAN、CAL_JULIAN、CAL_JEWISH
和 CAL_FRENCH。
calendar
要转换的历法，可以是 CAL_GREGORIAN、CAL_JULIAN、CAL_JEWISH、CAL_FRENCH 中的一个。
month
数字类型的月份，根据 calendar 来确定有效范围。
day
数字类型的日期，根据选定的 calendar 来确定有效范围。
year
数字类型的年份，根据选定的 calendar 来确定有效范围。
儒略日数。
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.