Convert Julian Calendar Dates to Julian Day Numbers with PHP's juliantojd

PHP provides the built-in function juliantojd to convert a date expressed in the Julian calendar to its corresponding Julian Day Number.

Function signature

int juliantojd(int $month, int $day, int $year)

The Julian calendar is defined for years from 4713 B.C. to 9999 A.D. Although the function can technically handle dates earlier than 4713 B.C., such values are historically meaningless. The calendar was introduced in 46 B.C., became stable around the 4th century, and the start of the year varied across regions.

Parameters

month : integer from 1 (January) to 12 (December).

day : integer from 1 to 31.

year : integer from –4713 to 9999.

Return value

The function returns the Julian Day Number that corresponds to the supplied Julian calendar date.