Astronomical year numbering
Cassini gave the following reasons for using a year 0:
Fred Espanak of NASA lists 50 phases of the moon within year 0, showing that it is a full year, not an instant in time. Jean Meeus gives the following explanation:
Although he used the usual French terms "avant J.-C." (before Jesus Christ) and "après J.-C." (after Jesus Christ) to label years elsewhere in his book, the Byzantine historian Venance Grumel used negative years (identified by a minus sign, −) to label BC years and unsigned positive years to label AD years in a table. He did so possibly to save space and put no year 0 between them.
Date and time notation in Serbia
Years can be written either with four or two digits, and in the latter case, century is usually replaced with an apostrophe (31. 12. ’06.). Leading zero is rarely used, and in those cases which are considered bad practice, only with months (however it is also optional for the days) (6. 05. 2006.). When literal names of the months are used they are not capitalized, and the four-digit format for the year is always used (31. December 2006). Yet another alternative is to use Roman numerals to indicate the month. In this case a dot is omitted (31. XII 2006).