Gregorian calendar
The Gregorian calendar is internationally the most widely used civil calendar.[1][2][3] It is named after Pope Gregory XIII, who introduced it in October 1582.
The calendar was a refinement to the Julian calendar[4] involving a 0.002% correction in the length of the year. The motivation for the reform was to stop the drift of the calendar with respect to the equinoxes and solstices—particularly the northern vernal equinox, which was used to set the date for Easter. Many (but not all) countries that have traditionally used the Islamic and other religious calendars have come to adopt this calendar for civil purposes.
The Gregorian reform modified the Julian calendar's scheme of leap years as follows:
Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 are not leap years, but the year 2000 is.[5]
In addition to the change in the mean length of the calendar year from 365.25 days (365 days 6 hours) to 365.2425 days (365 days 5 hours 49 minutes 12 seconds), a reduction of 10 minutes 48 seconds per year, the Gregorian calendar reform also dealt with the accumulated difference between these lengths. The canonical Easter tables were devised at the end of the third century, when the vernal equinox fell either on 20 March or 21 March depending on the year's position in the leap year cycle. As the rule was that the full moon preceding Easter was not to precede the equinox, the date was fixed at 21 March for computational purposes and the earliest date for Easter was fixed at 22 March. The Gregorian calendar reproduced these conditions by removing ten days.[6]
The Gregorian calendar continued to use the previous calendar era (year-numbering system), which counts years from the traditional date of the birth of Jesus (Anno Domini), originally calculated in the 6th century by Dionysius Exiguus.[7] This year-numbering system, also known as Dionysian era or Common Era, is the predominant international standard today.[8]
References[edit]
- ↑ Introduction to Calendars. United States Naval Observatory. Retrieved 15 January 2009.
- ↑ Calendars Archived 1 April 2004 at the Wayback Machine by L. E. Doggett. Section 2.
- ↑ The international standard for the representation of dates and times, ISO 8601, uses the Gregorian calendar. Section 3.2.1.
- ↑ See Wikisource English translation of the (Latin) 1582 papal bull Inter gravissimas.
- ↑ Introduction to Calendars. (15 May 2013). United States Naval Observatory.
- ↑ Ziggelaar (1983), p. 223.
- ↑ Nineteen-Year Cycle of Dionysius. Introduction and first argumentum.
- ↑ The first known occurrence of Common Era in English dates to 1708. Years before the beginning of the era are abbreviated in English as either BC for "Before Christ", or as BCE for "Before the Common Era" Two era names occur within the bull Inter gravissimas itself, anno Incarnationis dominicæ ("in the year of the Incarnation of the Lord") for the year it was signed, and anno à Nativitate Domini nostri Jesu Christi ("in the year from the Nativity of our Lord Jesus Christ") for the year it was printed. Les canons of Les textes fondateurs du calendrier grégorien (French)
