Old Style and New Style dates

Old Style (O.S.) and New Style (N.S.) indicate dating systems before and after a calendar change, respectively. Usually, this is the change from the Julian calendar to the Gregorian calendar as enacted in various European countries between 1582 and 1923. The Latin abbreviations may be capitalised differently by different users, e.g., St.n. or St.N. for stili novi. There are equivalents for these terms in other languages as well, such as the German a.St. ("alter Stil" for O.S.).

History

Since a Julian calendar year, with an average of 365.25 days, is about eleven minutes longer than the solar year, the astronomical start of spring shifted by one day to an earlier calendar date approximately every 130 years. In 1582, before the correction by the Gregorian calendar reform in the same year, it fell on March 11th. This meant that, during its existence, the astronomical events in the solar year of the Julian calendar had shifted 10 calendar days earlier. Since 19 Julian years are approximately 0.06 days longer than the 235 synodic months of the lunar circle, the calculated (“cyclical”) shifts from the astronomical full moon time approximately every 16 19-year periods (i.e. approximately every 300 years). one day later in the Julian calendar (the astronomical full moon time was ahead of that calculated based on the Julian calendar). As a result, the date of Easter, which depends on the date of the beginning of spring and the date of the spring full moon, was no longer correctly determined.

Old Style (O.S.) and New Style (N.S.) are sometimes used with dates to indicate whether the Julian year has been adjusted to start on 1 January (N.S.), even though documents written at the time use a different start of year (O.S.), or whether a date conforms to the Julian calendar (O.S.), formerly in use in many countries, rather than the Gregorian (N.S.). Closely related is double dating, which uses two consecutive years because of differences in the starting date of the year, or includes both the Julian and Gregorian dates. Beginning in 1582, the Gregorian calendar replaced the Julian in Catholic countries. This change was also implemented in Protestant and Orthodox countries some time later. In England and Wales, Ireland, and the British colonies, the change of the start of the year and the changeover from the Julian calendar occurred in 1752 under the Calendar (New Style) Act 1750. In Scotland, the legal start of the year had already been moved to 1 January (in 1600), but Scotland otherwise continued to use the Julian calendar until 1752. Many cultures and countries now using the Gregorian calendar have different old styles of dating, depending on the type of calendar they used before the change.

The German Jesuit Christophorus Clavius (1538–1612), who taught mathematician at the Collegio Romano in Rome, was commissioned by the Pope to work out the mathematical elaboration of the new calendar. He largely followed the suggestions of the physician and astronomer Aloisius Lilius. The reform took place through the papal bull Inter gravissimas curas of 24 February 1582. Parallel to the calendar reform, not simultaneously with it, the beginning of the year was postponed to January 1st (circumcision style), which was suitable as New Year's Day due to its name (Latin ianua means "door") and the proximity to Christmas and the winter solstice; In addition, the Roman tradition was preserved there. In the Middle Ages, the year otherwise began on different days, including Christmas, Easter and the Annunciation style. Nevertheless, the Gregorian reform had an influence, because the papal bull included a list of the new name days of the saints, which listed the remaining holidays of 1582 up to December 31 and those of the entire following, newly divided year (and all future ones). This resulted in overlaps of eleven days (Gregorian/Julian calendar) and at the same time one year (between New Year and Easter): “on 10/21 February 1750/1751”.

This calendar was eventually adopted by all Christian nations, which included the Papal States (and most Italian states), Poland-Lithuania, Kingdom of Spain, Kingdom of Portugal and their colonies, the Kingdom of France and colonies, Province of Holland and Province of Zeeland of the Republic of the Seven United Provinces, and the Holy Roman Empire of the German Nation, beginning with the Catholic territories (Corpus Catholicorum), Imperial city of Augsburg in January 1583, Duchy of Bavaria in October 1583, Imperial city of Cologne in November 1583, the Archduchy of Austria in January 1584 and so on. The Protestant territories of the Reich (Corpus Evangelicorum) aadopted the reform on 1 March 1700.

In Russia, Gregorian calendar dating firstcame into use in early 1918, when 31 January 1918 was followed by 14 February 1918. There had been a 13-day difference between Julian calendar and Gregorian calendar dates since 1 March 1900. It is common in English-language publications to use the familiar Old Style and/or New Style terms to discuss events and personalities in other countries, especially with reference to the Russian Empire and the very beginning of Soviet Russia.