Calendar Date Issues

See also:

Ambiguous Dates

Before getting on to real issues, I'd like to mention an annoying practice that people should try to avoid. It is currently common practice to write a western-style date only as numbers, such as 10/8/73. However, this number doesn't mean the same thing in all places. For some, it is 10 August (U.S. and three or four other countries), for others it is 8 October (most of the rest of the world). If the year is given as two digits and is less than 12, this can add to the problems, as some notations will use it at the beginning of the date.

I would suggest always using a month name or abbreviation such as 10 Oct or to use some other distinction (see Quaker Dates below). The month name abbreviation is the convention used on this site. A down-side of the actual month name or abbreviation is the fact it is language-specific.

If language independence is a priority, one can use the ISO 8601 format, which takes the form yyyy-mm-dd where yyyy is the four-digit year, mm is the two-digit month, and dd is the two-digit year. The month and year must be two digits, using a leading 0 for values less than 10 (i.e., 01, 02, 08, etc.). I know of no usage that reverses the day and month in this format. This also has advantages in spreadsheets and other computer use, since the format is always 10 characters, and will sort in an expected way.

A second point is the common practice of using only two digits for a year. For an historical date, it is vital to have a context for the year. It would be far better to write the full four digits. (The use of two digits was vital in the early years of computers, which had limited memory resources, but it is useless today.)

Julian Calendar

The Julian Calendar was created by Julius Caeser and the Egyptian astronomer Sosigenes, and took effect in 45 b.c.e over most of the Roman empire. This was the year 709 a.u.c in the Roman calendar, where a.u.c stands for ab urbe condita, or “from the founding of the city.”

The calender was a tremendous improvement over the existing Roman calendar, and in it you see most of the familiar parts of today's standard civic calendar. The year begins on 1 Jan, there are twelve months, the normal year is 365 days long and the leap year adds a day in February.

The basic aspects of his calendar that differ from the current calendar are the lack of weeks, a change to the number of days for certain months, and of course, the year number. Some month names have changed as well, and not just from the Latin form. However, these conditions were all changed well before most genealogies will be able to reliably trace a lineage so they should be of little concern. (And if you were able to reliabily trace a lineage that far, you should already be familiar with these details.)

Gregorian Adjustment

By the sixteenth century, the Julian calendar was significantly out-of-sync with the actual year and the date of Easter was becoming a problem, so a fix had to be made. This change was mandated in a papal bull from Pope Gregory XIII in 1582, using ideas that had in large part been determined decades before, but had remained unimplemented. The fix consisted primarily of two changes:

  1. Improve the leap year rule.

  2. Correct the current date.

The first change corrected the leap year rule slightly. Although the discrepency between the calendar and the length of the real year (the time to complete exactly one full orbit around our sun) may have been known since Julius Caeser's time, there was no fix defined for it. And while the Gregorian fix is still not perfect, the discrepency is less than a day in the next thousand years. Since this simple change only altered how often a leap year occured, it had no immediate effect on the people who used it.

The second change was more disruptive, and required the existing calendar to be brought into line with the real year. Since the existing calendar was ahead of where it should have been by a few days, these days had to be dropped, which required active change by the various locations as they adopted the new calendar.

Following this edict in 1582, Europe had the most accurate solar calendar in the world. The Catholic countries, anyway. Unfortunately, some areas were slower to adopt the new calendar than others, sometimes for religious reasons, so the change was protracted: the first countries to transition from the Julian to Gregorian calendar did so in 1582 (making 1583 the first full “modern” year), the last county did so in 1923.

Countries which were not using the Julian calendar at the time also changed on their own schedules. However, this shouldn't have the level of confusion that would be present in the switch from the Julian calendar.

For a table of the years of change (and the days removed), click on Gregorian Calendar Adjustment.

“New Style” Calendar, “Old Style” Calendar, Dual Years, Dual Dating

The first day of the year in countries using the Julian calendar often varied from the Julian calendar's specified 1 Jan. As a result, people who were aware of the difference during the years in which the Julian and Gregorian calendars co-existed would often use a dual-year format (for example, 1732/3) in official dates. This most commonly applied to England and its territories, but may also have been used in other locations.

For a discussion of this and a table of when countries changed, click on Beginning of the Year.

Quaker Dates

Although a lot is made of Quaker dates, they are really the same as dates written elsewhere in England. Thus they also used dual years, and converted to the Gregorian calendar at the same time as the rest of England and its colonies.

The only signficant distinction is that Quaker dates generally don't use month or day names. The months September through December are not a problem, since the names simply mean the seventh, eigth, ninth, and tenth months, respectively. (These names were from before the Julian reform, when the original Roman calendar's year started in March, and continued to work in England prior the Gregorian adjustment, as it's year started in March.) However, the other months, as well as the days of the week, were named for pagan gods and emperors, making them counter to Quaker teachings, and thus not to be used.

When reading a Quaker date, the format will also often add “mo” or “da” to ensure there is no confusion between month and day. For example, 3 Jan 1732 might be written 11mo 3da 1732/3. Remember that prior to 1753 in England and its colonies, the numeric year started in March, so January was the 11th month, and dual dates were often used for January, February, and part of March. There are variations on this theme, but these are all minor and should be very easy to understand.

Another format you might encounter is to use a Roman number for the month. For example, 3 VI 1764 would be 3 Jun 1764.

Julian Dates vs. Julian Calendar Dates

I often see references to Julian Dates when authors are refering to the Julian calendar. While this is technically correct, it is also misleading. The term "Julian calendar date" would be preferable.

The terms Julian Date and Julian Day refer to a calendar system that was developed by astronomers and is currently in use to simplify the mathematics of time-keeping. They are references to the number of days since the first day of 4713 b.c.e of the Julian calendar, and beyond the name itself, have nothing else to do with the Julian calendar.

In particular, there are no months or years in a Julian Date, it is purely a count of days. Converting the Julian date to a Julian or Gregorian calendar date (or vice-versa) requires a multi-step calculation.