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Calendars: Lunar, Metonic, Roman, Julian, Gregorian, etc.

PostPosted: Sat Jan 02, 2010 2:28 pm
by bimjim
Calendars: Lunar, Metonic, Roman, Julian, Gregorian, etc.

Calendars Explained

What could be simpler than a calendar? The printed one from the local real estate office shows twelve months, each with 28 to 31 days. Simple, right?

Well, it hasn’t always been so simple. After all, I keep stumbling upon genealogy records that are logged with “double dates.” That is, a birth record might state “22 February 1732/3.” Which was it: 1732 or 1733? Well, it actually was both. Just to make things more complex, most of our ancestors didn’t know what day it was. You see, most people in the early 1700s were illiterate. They couldn’t read a book, much less a calendar. Most people did not know what day it was or even how old they were. Very few remembered their own birthdays.

Throughout history, learned men kept track of the days, months, and years in a variety of ways. The ancient Egyptians began numbering their years when the star Sirius rose at the same place as the Sun. The Egyptian calendar was the first solar calendar and contained 365 days. These were divided into twelve 30-day months and five days of religious festival.

The calendar used by the ancient Greeks was based on the Moon and is known as the Metonic calendar. This calendar was based on 235 lunar months that made up almost exactly 19 solar years. This 19- year cycle became known as the Metonic cycle. However, given a nominal twelve-month year, an additional lunar month was needed to synchronize the cycle. These were added in years 3, 5, 8, 11, 13, 16, and 19 of the cycle. The Greek calendar was modified several times over the years to compensate for its inaccuracies.

The original Roman calendar was a mess. It originally started the year with the vernal equinox and consisted of 10 months (Martius, Aprilis, Maius, Junius, Quntilis, Sextilis, September, October, November, and December) for a total of 304 days. The 304 days were followed by an unnamed, unnumbered period, simply called “winter.” The Roman emperor Numa Pompilius (715-673 BC) introduced February and January between December and March, increasing the length of the year to 354 or 355 days.

In the year 46 BC, Julius Caesar reformed the calendar to a more manageable form. The Julian Calendar consisted of cycles of three 365-day years followed by a 366-day leap year. New Year’s Day was celebrated on March 21, the vernal equinox (first day of spring). The calendar was called the Julian Calendar, named after Julius Caesar.

The Venerable Bede, an English scholar who lived from 673-735, noted that the vernal equinox had slipped three days earlier than the traditional March 21. He proposed changes to the calendar, but the changes were not adopted for another 850 years.

By the year 1582, the calendar had slipped to become eleven days off. To make up the difference, Pope Gregory XIII decreed that the day after October 4, 1582, would be October 15, 1582. In other words, everyone lost eleven days. Because of the Pope’s decree, the reform of the Julian Calendar came to be known as the Gregorian Calendar.

The Catholic countries of France, Spain, Portugal, and Italy followed this decree immediately. Various Catholic German countries (Germany was not yet a unified nation), Belgium, the Netherlands, and Switzerland followed within a year or two, and Hungary followed in 1587.

The Protestant German countries adopted the Gregorian reform in 1700. By this time, the calendar trailed the seasons by twelve days. England finally adopted the Gregorian Calendar in 1752, declaring that Wednesday, September 2, 1752, was immediately followed by Thursday, September 14, 1752. America was a part of England at the time, so the Americans adopted the new calendar on the same date. Their neighbors in Canada had always used the Gregorian Calendar because the land had been settled by the French, who had used the new calendar since 1582. In the 1600s and early 1700s, crossing the border from the British Colonies to the French Colonies meant a change of eleven or twelve days on the calendar!

Turkey and Russia did not change to the new calendar until the early twentieth century. In Greece, 9 March 1924 was followed by 23 March 1924.

Sweden decided to make a gradual change from the Julian to the Gregorian Calendar. By dropping every leap year from 1700 through 1740, they gradually omitted the eleven superfluous days.

The year 1700 (which should have been a leap year in the Julian Calendar) was not a leap year in Sweden. However, by mistake, the Swedish government listed 1704 and 1708 as leap years. This left Sweden out of synchronization with both the Julian and the Gregorian world, so they decided to go “back” to the Julian Calendar. In order to do this, they inserted an extra day in 1712, making that year a double leap year! So in 1712, February had 30 days in Sweden. Babies born the last day of that month had a very unique birthday!

Some religious sects still use a lunar-based calendar to determine holidays. Easter, for instance, generally occurs on the first Sunday following the first full moon after the vernal equinox, although the actual scheme is a bit more complicated.

To summarize, the Julian Calendar was slightly too long, causing the vernal equinox to slowly drift backwards in the calendar year. The Gregorian Calendar system dealt with these problems by dropping a certain number of days to bring the calendar back into synchronization with the seasons, and then slightly shortening the average number of days in a calendar year by omitting three Julian leap-days every 400 years. Even the Gregorian Calendar we use today is not perfect: astronomers and mathematicians tell us that it is off by one day every 4,000 years.

Under the older Julian Calendar system, while New Year’s was celebrated on March 21, the calendar actually began with January. Therefore, any date between January 1 and March 21 was written as a combination of two years. A child born in what is now the United States on February 3 in what we now call 1726 would have a birth date of 3 February 1725/6. Even more confusing, dates between January 1 and March 21 in a year ending in a nine would have a “/0″ added, as in 3 February 1729/0. The dates written with a slash followed by another digit are referred to as “Old Style” dates.

Of course, the loss of eleven or twelve days on the calendar certainly confused the calculations often found on tombstones proclaiming that someone died at the age of 76 years, 4 months and 12 days!

When researching old records, the genealogist may often encounter “Old Style” dates such as 3 February 1727/8. Recording such dates on paper is usually simple. However, computer programs may have difficulties.

All of the better genealogy programs of today can accept Old Style dates such as 3 February 1727/8. They will even properly calculate ages from tombstone information listed as “3 February 1729/0.” In fact, most genealogy programs written in English will assume that any date entered prior to September 14, 1752 is a double date year. At least one genealogy program allows the user to specify a different year as the date of conversion from the Julian Calendar to the Gregorian. This is fine for anyone who has all ancestors living in any one country, but it creates a problem for those of us with ancestors from two, three, or more countries.

For instance, my English-speaking ancestors all converted from Julian to Gregorian on September 14, 1752. However, my French-speaking ancestors converted their calendars about one hundred seventy years earlier, on October 15, 1582. If I had Russian ancestry, they would not have converted until 1917. Then there are the Swedes… . What is a person of mixed ancestry to do?

You can convert Julian dates to Gregorian and vice-versa at Since this is a web site in English, it seems to use the English date of September 14, 1752, as the date of conversion.

You can read more about the conversion to the Gregorian Calendar by looking at “Calendopaedia – The Encyclopedia of Calendars” at

Re: Calendars: Lunar, Metonic, Roman, Julian, Gregorian, etc.

PostPosted: Sat Feb 13, 2010 4:30 pm
by bimjim
Understanding Julian Calendars and Gregorian Calendars in Genealogy

We use calendars to keep track of time. They have been used throughout human history to record periods or events longer than a day. For example, agricultural societies use calendars based on the seasonal cycle of the sun to determine the correct time for the planting and harvesting of crops. Religious observances are often derived from calendars that follow the lunar cycle. Calendars continue to be used for these purposes, as well as to regulate civil life, commerce and scientific endeavours. It is important for anyone studying genealogy and family history to understand calendars.

The Gregorian calendar is the formal name for the calendar that most people use today. Other calendars, however, are still in use in some parts of the world. These include the Jewish calendar, the Islamic calendar and the Chinese calendar. All these calendars share one common trait. They are based on either the annual cycle of the sun, the phases of the moon, or a combination of the two. The Gregorian calendar, for example, is a combination of the annual cycle of the sun (to determine the length of the year) and the cycles of the moon (the word ‘month’ is derived from the word moon).

Calendars play an important role in genealogy. Genealogists researching family histories before 1752 must have a basic understanding of the Gregorian calendar and its predecessor, the Julian calendar in order to correctly interpret old dates. To understand why, a bit of history is required.

Julian Calendar

The Julian calendar was implemented by the Romans in 46 B.C. under the guidance of Julius Caesar (and thus the name Julian calendar). Julius Caesar wanted a more accurate calendar for agricultural purposes. At the time, the Roman Empire was primarily agricultural. Although its exact origins are not known, the Julian calendar was almost certainly derived in part from ancient Babylonian calendars, with additions from several other cultures. For example, the division of hours into 60 minutes and minutes into 60 seconds comes from the Mesopotamians, the division of the day into 24 hours comes from ancient Egyptian calendars and the division of the week into 7 days comes from the Jewish calendar.

Under the Julian calendar, which was based on the solar cycle, the year was divided into 12 months of 365 days. An extra day was added every fourth year. This resulted in a year having on average 365 ¼ days.

The Julian calendar was used in all the countries governed by the Romans. This included England and much of Europe. It continued to be used (and maintained) by the Roman Catholic Church, which inherited many Roman institutions after the downfall of the Roman Empire. As a result, the Julian calendar was in widespread use across much of Europe for many centuries.

Gregorian Calendar

The Julian calendar assumes the year is exactly 365.25 days long. Unfortunately, the actual solar year is slightly shorter (it is 365.242199 days to be exact). Although the difference appears minor, it can add up over the centuries. In fact, every 129 years, the Julian calendar slipped one additional day out of synchronization with the actual solar year.

This caused a problem within the Roman Catholic Church, who came to realize in the 1500’s that their reliance on the Julian calendar was causing them to incorrectly calculate the date of the spring equinox (the spring equinox is the one day in spring when there is exactly 12 hours of sunlight and 12 hours of darkness). Easter, one of the most sacred days in the Christian religion, is calculated from the spring equinox (Easter is the first Sunday following the full moon after the spring equinox).

To make matters worse, many other Christian observances (such as Lent, for example) are determined from the date of Easter. Therefore, if Easter were calculated incorrectly, then many religious observances would be celebrated on the wrong day. This caused considerable controversy within the Catholic Church and resulted in several commissions to try to find a solution. It cumulated with Pope Gregory XIII, who in 1582 issued a papal bull that resulted in several calendar revisions, the most important being:

• It established what is now known as the Gregorian calendar (named after Pope Gregory XIII).

• The new Gregorian calendar had an extra day in those years that were divisible by 4 (just like the old Julian calendar), but unlike the Julian calendar, it did not add an additional day in years that were divisible by 100, unless the year was also divisible by 400. Thus, under the Gregorian calendar, the years 1700, 1800 and 1900 were not leap years, but the years 1600 and 2000 were leap years.

• To make up for the errors in the old Julian calendar, ten days were omitted from the new Gregorian calendar. Thus, Thursday, October 4, 1582 in the old Julian calendar was immediately followed by Friday, October 15, 1582 in the new Gregorian calendar.

The Catholic countries of Italy, Spain, Portugal and Poland immediately adopted Pope Gregory XIII’s decree, with France and Luxembourg soon following. However, by the 1500’s the Roman Catholic Church’s influence on Europe had waned and some countries were either slow to adopt (such as Hungry in 1587), or were distrustful of the Roman Catholic Church and resisted adopting the new and improved calendar.

The notable standout was England and the English colonies (including America), which continued to use the Julian calendar long after most of Europe had switched to the Gregorian calendar. In fact, England and the colonies did not adopt the Gregorian calendar until 1752, almost 170 years after Pope Gregory XIII’s decree. However, by that time the Julian calendar had slipped 11 days relative to the Gregorian calendar.

When England and the colonies finally adopted the Gregorian calendar, it was necessary for them to omit 11 days to ‘catch up’. As a result, for England and the colonies, Wednesday, September 2, 1752 in the old Julian calendar was immediately followed by Thursday, September 14, 1752 in the newly adopted Gregorian calendar. The days in between these two dates officially do not exist.

How to Interpret Old Dates in Genealogy

Using England and the colonies as an example, genealogists need to be aware of two things when interpreting old records after 1752. First, in many countries (including England) the general population continued to use the old Julian calendar long after the country officially adopted the new Gregorian calendar. This is particularly true of dates recorded in personal family records and documents, as opposed to official records, which usually used the Gregorian calendar.

Sometimes it is evident which calendar was used by how the date was written down in an old record. For example, dates recorded by the Julian calendar sometimes had a notation “O.S.” for Old Style, while dates recorded by the Gregorian calendar were marked as “N.S.” for New Style.

Secondly, different countries used different days to mark the beginning of the New Year. Depending on the country (and the region within some countries!), the first day of the New Year could be December 25, January 1, March 1, March 24 or March 25. Britain and the colonies prior to 1753 typically used either March 24th or March 25th as the beginning of the New Year. This roughly corresponded to the spring equinox.

Recording Old Dates in Genealogy

When recording old dates for genealogy, you can enter either a Julian date or a Gregorian date provided that you carefully record which calendar is being used. Alternatively, you can convert old Julian dates to the Gregorian date equivalent and enter the Gregorian date into your records, with a notation that it is a Julian date converted to a Gregorian date. When you are uncertain whether the date is a Julian date or a Gregorian date, then this should also be noted.


Example: Converting a Julian Date to a Gregorian Date

A person is born in England on March 1, 1751. Since this date is before September 1752, we can be reasonably certain the date has been recorded using the Julian calendar system. To convert this Julian date to the equivalent Gregorian date, it is necessary to do the following:

Step 1: Add 11 days. Thus, March 1 becomes March 12.
Step 2: (this step is only necessary if the Julian date is between January 1 and March 25). Add one year. Thus, 1751 becomes 1752.
Thus, the equivalent Gregorian date is March 12, 1752.


Some people who keep genealogy records prefer to write a Julian date of March 1, 1751 using the notation March 1, 1751/52. Genealogy In Time™ recommends you do not use this format because this notation is neither a Julian date nor a Gregorian date. The correct Julian date is March 1, 1751 and the correct equivalent Gregorian date is March 12, 1752. March 1, 1751/52 is technically not a date, so do not use it.

The importance of proper date notation can perhaps best be highlighted by using George Washington’s birthday as an example:


George Washington was the first President of the United States and a pivotal figure in early American history. He was born on February 11, 1731 in Westmoreland county, Virginia.

At the time, America was an English colony, so it used the Julian calendar. In the Julian calendar, George Washington’s birthday was February 11, 1731, but in the Gregorian calendar it is February 22, 1732.

This is the reason why (to this day) the United States celebrates George Washington’s birthday every year with an official holiday on February 22nd (the correct Gregorian date) and not on February 11th (the old Julian date).


Fun Gregorian Calendar Facts

Here are a couple of fun facts about the introduction of the Gregorian calendar that will be appreciated by anyone studying genealogy.

• A modern measurement of the length of the actual solar year shows that in 1582 Pope Gregory XIII should have removed 12 days from the calendar instead of ten days.

• It is easy for us to sit here today and think that Pope Gregory XIII had an easy decision in issuing a decree eliminating ten days from the calendar. However, at the time, the decree was not well received by the general population. People thought skipping ten days in the new calendar meant their life had been shortened by ten days!

• The Roman Catholic church knew for quite some time that they were calculating the date of the spring equinox incorrectly (since all that was necessary was for someone to measure the amount of daylight to find the day each Spring that had exactly 12 hours from sunrise to sunset). However, the issue was not acknowledged by the church until it became evident to many people that there was a problem.