Calendar History, by Mary Penner

calendarWhile hanging out along the Nile River with Cleopatra, Julius Caesar may have picked up the idea of using the sun to calculate the length of the calendar year from Egyptian astronomers. The roughly 355 day Roman calendar was an irksome mess that needed regular tinkering to align it with the seasons.  Days or months were inserted or taken away every now and then.  This was understandably annoying to the populace.

When Caesar returned triumphantly to Rome in 47 B.C., he decided to launch a new calendar similar to the Egyptian model.  The new solar calendar had a 365 day and 6 hour year with an extra day thrown in every four years to account for the extra hours. After a vexing year of calendar adjustments making 46 B.C last 455 days, the new calendar, known as the Julian calendar, commenced on January 1, 45 B.C.  The Julian calendar would reign for centuries to come.
The Julian calendar, though, contained a central flaw; each year was 11 minutes too long.  That seems insignificant, but over hundreds of years that extra time added up to a calendar careening out of sync with the natural world. To further complicate matters, some groups jettisoned January 1 as the first day of the year and adopted other days that suited them better. Some chose March 1 as New Year’s Day; others opted for September 1, September 24, or December 25.  Another popular choice for New Year’s Day was March 25.  The British latched onto this date; so, American colonists brought that calendar quirk with them across the Atlantic.

Through the centuries various scientists and astronomical thinkers sounded the alarm about this calendar chaos, and some world and religious leaders undertook futile attempts to make changes. But, order wasn’t restored until 1582 when Pope Gregory XIII decreed a calendar change.  New Year’s Day fell on January 1 again, and the calendar year was shortened to 365 days, 5 hours, 48 minutes, and 20 seconds.  Further adjustments were made to leap years.

Unfortunately for the Pope and his reform efforts, many people ignored him.  So, the Gregorian calendar was adopted piecemeal over time by different countries.  The British as well as their Colonies in America were staunch holdouts and didn’t adopt Gregory’s calendar until 1752. So, 1751 in America ended on December 31 instead of March 24 making that year have only 282 days.  Plus, eleven days, September 3-13, were skipped in 1752 in order to catch up with the Gregorian calendar.

These calendar somersaults have several implications for genealogists:

1. You will often see double dates for events that occurred in January, February, or March.  For example, the marriage date of Patience Toogood and Joseph Bozworth in Rhode Island was recorded as March 4, 1735/1736.  They didn’t get married twice.  It was 1735 in the Colonies, but much of the rest of the world considered it to already be 1736.

2. You might find children with seemingly miraculous birth dates.  Benjamin’s birth might be November 2, 1745 and his sister’s birth might be March 2, 1746.  They weren’t born 4 months apart; they were born 16 months apart.

3. Sometimes you will see O.S. or N.S. written by dates to indicate Old Style for the Julian calendar and New Style for the Gregorian calendar.  When documenting your research, always try to indicate O.S. or N.S. if you know which calendar was being used.

4. When doing foreign research, find out when that country adopted the calendar changes.  See Calendars Through the Ages for a partial listing of some of the worldwide calendar dramatics.

Genealogist Mary Penner writes Lineage Lessons, a weekly genealogy column, for the Albuquerque Tribune ( She can be reached at



2 thoughts on “Calendar History, by Mary Penner

  1. Fascinating! This is staying in my “Important things to remember file!” We take so many things for granted in our life. I can’t imagine what kind of confusion this caused!

  2. Several nice additions to my personal write-up of the history of various different calandars. When Caesar was with Cleopatra I am sure he had other things on his mind rather than the calendar!

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