Legal Definitions - old style

Old style refers to the Julian calendar system, a method for organizing time that was widely used before the adoption of the modern Gregorian calendar. Introduced by Julius Caesar in 45 BCE, this calendar system established a year as having 365 days, with an extra day added every four years (a leap year) to account for the Earth's orbit around the sun. This meant that, on average, a Julian year was considered to be exactly 365.25 days long. However, the actual astronomical year is slightly shorter than 365.25 days. Over centuries, this small discrepancy caused the old style calendar to gradually drift out of sync with the seasons, leading to a noticeable error in the timing of events like equinoxes and solstices. This cumulative error eventually prompted the reform of the calendar by Pope Gregory XIII in 1582, leading to the "new style" or Gregorian calendar we use today.

• A historian is examining a letter written in England in 1570, which is dated "March 10, 1570 (o.s.)". The "o.s." indicates that the date is according to the old style Julian calendar, which was still in use in England at that time. If the historian needed to compare this date to an event recorded using the modern Gregorian calendar, they would have to account for the difference in dating systems, as the Julian calendar had fallen behind the astronomical year.

• Many Eastern Orthodox churches celebrate Christmas on January 7th, while most Western Christian denominations observe it on December 25th. This difference arises because the Eastern Orthodox churches continue to follow the old style Julian calendar for their liturgical calendar. Due to the Julian calendar's accumulated error, January 7th on the Gregorian calendar corresponds to December 25th on the Julian calendar, illustrating how the old style system results in different dates for fixed holidays.

• When researching the birthdate of a historical figure like Miguel de Cervantes, who died in Spain in 1616, one might encounter his birth year as 1547. Spain had adopted the Gregorian calendar in 1582. Therefore, any dates for events in Cervantes's life prior to 1582 would have been recorded using the old style Julian calendar, even if later historians convert them to Gregorian dates for consistency. This highlights the period when the old style calendar was the standard for record-keeping in many parts of the world.