Julian vs. Gregorian Calendars

Why you sometimes see two dates for the same event

Occasionally, on some Polish (and Eastern European) records, two dates are recorded for the same event. This is because two different calendars have been used in different parts of the world: the Julian Calendar (“Old Style”, OS) was used by Russian administration & the Orthodox Church. The Gregorian Calendar (“New Style”, NS) was used by Western Europe and the Catholic Church. From the late 1700s through the early 1900s, during the partitions, parts of Poland were ruled by different empires that used these different calendars at the same time. The calendars drifted apart over time.

In areas under the Russian Empire (Congress Poland), Civil law required Julian dates. But Catholic practice followed Gregorian dates. To avoid legal or sacramental disputes, priests often recorded both. You’ll often see dates written like this: 7 / 19 January 1858, or this: 19 January (7 January O.S.), or this: 7 stycznia / 19 stycznia. These are the same day, expressed in Julian first, Gregorian second. Most commonly, this is seen in marriage and death records written by Catholic priests in Congress Poland between 1808-1867. For genealogy purposes, always convert to Gregorian for modern use. But it is good practice to record both when both are shown.

For our family history, this comes in to play on our Brodzinski branch, since they resided in "Congress Poland" ruled by Russia. To simplify as it pertains to us, for any Julian dates encountered in the Rypin area during the 1800's, simply add 12 days to get the Gregorian date.

For a much more detailed description of Julian vs. Gregorian, visit Stephen P. Morse's webpage: https://stevemorse.org/juliancalendar/julian.htm
He has also developed an excellent conversion tool for converting between Julian and Gregorian dates, found here: https://stevemorse.org/jcal/julian.html