Genealogists and the Julian Calendar
Double Dating in 1700s Explained
Aug 22, 2009 Rosemary E. Bachelor
Beginning genealogists are often puzzled when they find, in genealogical publications, dates expressed like this: Arnold Bennett (Oct. 4, 1746/7). In mankind’s vision of time the 1752 gap is the dividing line between OS (“old style”) and what today we know as our reckoning of time, calendar style.
The earliest calendars varied. Egyptians based their year on the appearance of the Dog Star (Sirius) in the eastern sky just before sunrise. Later, they based it upon the sun. They divided the year into 12 months of 30 days each and added 5 days at the end of each year. The Babylonians and Greeks followed a similar formula.
History of Calendars
The Hebrew calendar began with their guess at the date of creation. It was 3760 years before the Christian era. To find the year in the Hebrew calendar, add 3761 to the Gregorian calendar date. The Islamic calendar begins with Mohammed’s flight from Mecca. That would be 622 A.D. by the Gregorian calendar. The old Roman calendar was the most confused. It had a year 10 months long and dated from the founding of Rome (the year 753 B.C. by our current calendar). The year Julius Caesar was killed is 44 B.C. in our calendar, but about 709 to Romans.
The Roman calendar became the subject of abuse. Months were added to increase taxes or help public officials stay in office. By the time of Julius Caesar, the sun crossed the equator in the equinoxes three months from the time the calendar said it should. This made the seasons three months behind.
The Julian Calendar
The first modern calendar was put into use by Julius Cesar, who decreed there would be three years of 365 days each, then one year of 366 days. That is what led to us having an extra day every fourth February (leap year). The Julian calendar was an improvement, but still not entirely accurate. It was off 11 minutes a year and by 1580 the spring equinox fell on March 11, 10 days earlier than it should have.
The Gregorian Calendar
The final calendar correction was done in 1582 by Pope Gregory XIII; the calendar we now use is called the Gregorian calendar. The first countries to adopt the Gregorian calendar were Roman Catholic. Most Protestant countries adopted it later.
The Gregorian calendar system is fairly complex, but its correctional factor means that the error in our present calendar is less than one day every 3000 years. It has been estimated that our calendar will be one day ahead of the sun in the year 4316.
When the Year Began
In former years, the year had begun in March, not January. In England, even before 1752, 1 January was sometimes treated as the start of the new year. For awhile, the year starting in March was considered the civil or legal year. To reduce misunderstandings about the date, it was not uncommon in parish registers for a new year heading after 24 March, for example 1661, to have another heading at the end of the following December indicating "1661/62". This was to explain to the reader that the year was 1661 Old Style and 1662 New Style.
American Calendar
American colonies made the switch from the Julian to Gregorian calendar in 1752, when the whole British Empire changed. Sept. 2 was followed by Sept. 14. An adjustment was needed. Dates preceding the change are now noted as OS (old style). An example: George Washington’s birthday is really Feb. 11, 1732 (OS) and only after the change to the Gregorian calendar was his birthday established as Feb. 22, 1732
Most pre-1752 dates in American history have been converted to New Style, meaning Gregorian dates. Some countries did not convert to the Gregorian calendar until the early 1900s.
The Conversion Equation
To make the conversion from Julian dates to Gregorian dates, add 10 days to the Julian date between Oct. 5, 1582, through Feb. 28, 1800. Then, add 11 days to Julian dates from March 1, 1700 through Feb. 28, 1800, and add 13 days to Julian dates from March 1, 1900 through Feb. 28, 2100. The rest? That’s for future generations to worry about!
A companion article discusses correct entry of dates (1732/1733 versus 1732-1733) on ancestor charts.
Source: "History of the Calendar," The Dinghy, Vol. 2, No. 6 (December, 1989).
New Calendar Was Ushered in by Pope Gregory XIII
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