In the articles and software on this web site all Julian day numbers are chronological Julian day numbers unless specified otherwise. For dates in the period from 1859 to about 2130 only five digits need to be used to specify the date rather than seven. This concept is similar to that of the Julian day number. 16 October 1582 is Lilian day 2, and so on. Conversion Algorithms Mathematicians and programmers have naturally interested themselves in mathematical and computational algorithms to convert between Julian day numbers and Gregorian dates.
Division is to be understood as in integer arithmetic, with remainders discarded.
These algorithms are valid only in the Gregorian Calendar and the proleptic Gregorian Calendar . They do not correctly convert dates in the Julian Calendar. This algorithm handles dates in the Julian Calendar as well as dates in the Gregorian Calendar.