Understanding the Julian to Gregorian Calendar

Gregorian CalendarNumerous times you will see where an ancestor’s birth, marriage or death date are written May 11, 1712/1713 and you are not sure which year the event actually occurred.  This is due to a change in the type of calendars used and when they were adopted. First, an explanation of each calendar.

The Julian calendar was created by Julius Caesar back in 46 B.C. by having the best philosophers and mathematicians of his time to improve the older Roman calendar that followed the lunar cycles. The Julian had set number of days for each month, with just twelve months for a year and 365.25 days for each year. That gave the fourth year with an extra day, the leap year. It had every centennial year (1100, 1300, 1500, etc) as a leap year also.  Corrections over nearly 45 years to the Julian were made as it adjusted the number of days in a month.

By the 1580s it was found that the actual number of days in a year should be 365.242199.  Over the centuries of using the Julian calendar there needed to be a recalculation of eleven days to get the calendar in alignment. Also the vernal equinox had gotten out of line.

So it was the Roman Catholic Pope Gregory XIII declared that a new Gregorian calendar was now necessary. There would be in 1582 an actual skipping of several days to get the days correct.  After Thursday of October 4, 1582, then the next day’s date would be Friday of October 15, 1582.  This allowed the vernal equinox to return to March 21st.   Another correction would have leap years if they were a multiple of 400.

However, not all world locations accepted this new Gregorian calendar right away, so creating even greater confusion. Those Catholic countries changed calendars immediately, but non-Catholic countries rejected the change. The United Kingdom and all their colonies, like the American Colonies, did not recognize the Gregorian calendar (also known as Western or Christian Calendar) until September 1752, so leading to the main reason for two different years on many records; such as 1712/1713.

A few of the last countries to switch to the Gregorian calendar were Russia in January 1918, Greece in February 1923 and Turkey in 1926.  They had to drop 13 days from their calendar to get the days in line.

To assist the family history researcher in figuring dates, review these Calculators and Converters via Cyndi’s List.

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