Robert's Genealogy Pages

Calendar links

With the third millennium upon us, some information has appeared on the web to help educate us on the issue.

Millennium - U.S. Naval Observatory

Julian vs. Gregorian Calendars

The Egyptian solar calendar was adopted by Julius Caesar, becoming the calendar standard for sixteen hundred years. The Julian Calendar was fairly simple: 365 day years with a quadreninial leap year. But by 1582 this calendar was ahead by 10 days.

Pope Gregory XIII made three changes. He

advanced the calendar by 10 days, making the day after 4 October 1582 into 15 October,
declared that double zero years would be leap years only if they were divisible by 400,
and changed New Year's day from 25 March (Annunciation Day) to 1 January.

But Protestant England and America didn't change to the New Style dating until 1752. By this time the gap was 11 days (due to a Julian leap year in 1700) so the correction was to have 2 September 1752 followed by 14 September.

Under the Old Style (Julian Calendar) the range of months in the same year was
Mar(25-31), Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec, Jan, Feb, Mar(1-24).
This leads to the seeming error of having 23 April 1736 occuring before 19 February 1736 or the day after 24 Mar 1743 begin 25 Mar 1744. To handle this dating confusion, unless there are other dates to confirm which system was being used, double years are recorded, such as 23 Feb 1736/7, whenever a date for the years 1583 to 1752 falls between 1 Jan and 24 Mar. If it is clear which dating system was used, some people use the abbreviations O.S. (Old Style Julian) and N.S. (New Style Gregorian) after dates.

Here's a Unix command to try out:

> cal 9 1752
   September 1752
 S  M Tu  W Th  F  S
       1  2 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30

Which is documented in the man pages for that utility.