(PHP 4, PHP 5, PHP 7)
jdtounix — Convert Julian Day to Unix timestamp
$jday
   )
   This function will return a Unix timestamp corresponding to the
   Julian Day given in jday or FALSE if
   jday is not inside the Unix epoch
   (Gregorian years between 1970 and 2037 or 2440588 <=
   jday <= 2465342 ). The time returned is
   localtime (and not GMT).
  
jdayA julian day number between 2440588 and 2465342.
The unix timestamp for the start of the given julian day.