The following post was written by Brian Mulcahy, Reference Librarian at the Fort Myers-Lee County Library, and is shared here with his permission:
Calendars provide a method of measuring time and allow people to record and calculate dates and events. Genealogists encounter problems with differences in dates caused by the changeover from the Julian calendar to the Gregorian calendar in 1582. Individual countries, depending on their political and religious view of the Papacy and Pope Gregory, adopted this changeover at different times. Researchers must consult historical sources in Europe and the British Isles to determine which calendar was being utilized during a specific time period. Germany is an example of a country where the Protestant and Catholic regions utilized two different calendars simultaneously during this historical period.
Most of the civilized world adopted the Julian calendar (named in honor of Julius Caesar) around 45 BC. This calendar computed the solar year, the time it takes for the Earth to revolve around the sun, as 365 days and six hours. Three years each of which consisted of 365 days were followed by a fourth or leap year of 366 days. By the Julian calendar, March 25 was the first day of the year. During the Middle Ages, astronomers and mathematicians became aware of discrepancies in the Julian calendar. Dates were ahead of actual time by ten days. In 1582, Pope Gregory XIII commissioned a new calendar which became known as the Gregorian Calendar. This new calendar changed the first day of the year to January 1 and moved the current date ahead 11 days to make up for lost time.
While the Catholic countries of Europe adopted the Gregorian calendar as soon as copies of the Papal decree reached them, Protestant countries refused initially to adopt the change. Protestant states of the Holy Roman Empire, by the order of the Diet (Parliament) at Regensburg, dropped 11 days from the 19th to the 29th of February 1700, so that February 18th immediately became March 1st. Scotland which was still considered a separate kingdom before its union with England under James VI, converted in 1603 by order of the Privy Council.
The Gregorian calendar was not fully adopted in Colonial America until the mid-1700s. Until the new Gregorian calendar was adopted and the dates adjusted accordingly, New Years Day occurred in March. The designation of the New Year in Colonial America was used for the first time in the General Court of Connecticut as “this 20th day of March, 1649-1650” or 1650 by our present system of dating. This style of dating prevailed for almost 100 years. Due to an error in the Julian calendar, the dates in all months between 1600 and 1700 were carried forward eleven days. Thus, July 10 was really July 21 according to our present system of dating. In 1752, the British Parliament changed the calendar from the old style to the one used today, and changed the date on September 3, 1752 (old calendar) to September 14, 1752 (new calendar). Eleven days were thus eliminated.
Another confusing issue resulting from the switch was the practice of double dating. Double dating was used throughout the British Empire to clarify dates occurring between 1 January and 24 March on years between 1582 and 1752. In the ecclesiastical or legal calendar, March 25th was recognized as the first day of the year and was not double dated. Researchers of Colonial American ancestors will often see double dating in older records. Double dates were normally identified with a slash mark (/) representing the Old and New Style calendars, e.g., 1690/1691. Even before 1752 in Colonial America, some educated clerks knew of the calendar change in Europe and used double dating to distinguish between the calendars. This was especially true in civil records, but less so in church registers. Researchers will often see this type of double dating in New England town records, court records, church records, and wills, or on colonial gravestones or cemetery transcriptions. The system of double dating ended in 1752 in the American colonies with the adoption of the Gregorian calendar.
BLM 2/6/2012
