Valid Range for Julian Calendar 4713 B.C. to 9999 A.D.
Although this function can handle dates all the way back to 4713 B.C., such use may not be meaningful. The calendar was created in 46 B.C., but the details did not stabilize until at least 8 A.D., and perhaps as late at the 4th century. Also, the beginning of a year varied from one culture to another - not all accepted January as the first month.
Remember, the current calendar system being used worldwide is the Gregorian calendar. gregoriantojd() can be used to convert such dates to their Julian Day count.