Proleptic Gregorian calendar

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The proleptic Gregorian calendar is produced by extending the Gregorian calendar backward to the dates preceding its official introduction in 1582. In nations that adopted the Gregorian calendar after its official and first introduction, dates occurring in the interim period of 15 October 1582 (the first date of use of Gregorian calendrical dates, being dated 5 October 1582 in the preceding Julian calendar) to the date on which the pertinent nation adopted the Gregorian calendar and abandoned the Julian calendar are sometimes 'Gregorianized' also. For example, the birthday of U.S. President George Washington was originally dated 11 February 1731 (Old Style) because Great Britain, of which he was born a subject, used (until September 1752) the Julian calendar and dated the beginning of English years as 25 March. After Great Britain switched to the Gregorian calendar, Washington's birthday was dated 22 February 1732 proleptically, according to the Gregorian calendar applied backward. This remains the modern dating of his birthday. [1]

Contents

Usage

ISO 8601:2004 (clause 3.2.1 The Gregorian calendar) explicitly requires use of the proleptic Gregorian calendar for all dates before the introduction of 15 October 1582, if the partners to an exchange of information agree. Most scholars of Maya civilization also use it, [2] especially when converting Long Count dates (1st century BC – 10th century AD).

The best practice for citation of historically contemporary documents is to cite the date as expressed in the original text and to notate any contextual implications and conclusions regarding the calendar used and equivalents in other calendars. This practice permits others to re-evaluate the original evidence. [3]

For these calendars one can distinguish two systems of numbering years BC. Bede and later historians did not enumerate any year as zero (nulla in Latin; see Year zero); therefore the year preceding AD 1 is 1 BC. In this system the year 1 BC is a leap year (likewise in the proleptic Julian calendar). Mathematically, it is more convenient to include a year 0 and represent earlier years as negative numbers for the specific purpose of facilitating the calculation of the number of years between a negative (BC) year and a positive (AD) year. This is the convention in astronomical year numbering and the international standard date system, ISO 8601. In these systems, the year 0 is a leap year. [4]

Although the nominal Julian calendar began in 45 BC, leap years between 45 BC and 1 BC were irregular (see Leap year error). Thus the Julian calendar with quadrennial leap years was only used from the end of AD 4 until 1582 or later (contingent on the specific nation in question).

The proleptic Gregorian calendar is sometimes used in computer software to simplify identifying pre-Gregorian dates, e. g. in PostgreSQL, [5] MySQL, [6] SQLite, [7] PHP, CIM, Delphi and Python. [8]

Difference between Julian and proleptic Gregorian calendar dates

Before the official and first introduction of the Gregorian calendar, the differences between Julian and proleptic Gregorian calendar dates are as follows:

The table below assumes a Julian leap day of 29 February, but the Julian leap day, that is, the bissextile day (ante diem bis sextum Kalendas Martias in Latin) was accomplished by repeating 24 February (see Julian reform). Therefore, the dates between 24 and 29 February in all leap years were irregular.

Note: When converting a date in a year which is leap in the Julian calendar but not in the Gregorian, include 29 February in the calculation when the conversion crosses the border of February and March.

Julian RangeProleptic Gregorian RangeGregorian Ahead By
From 3 March AD 4
(beginning of quadrennial leap years)
to 1 March 100		From 1 March AD 4
to 28 February 100		−2 days
From 2 March 100
to 29 February 200		From 1 March 100
to 28 February 200		−1 day
From 1 March 200
to 28 February 300		From 1 March 200
to 28 February 300		0 days
From 29 February 300
to 27 February 500		From 1 March 300
to 28 February 500		1 day
From 28 February 500
to 26 February 600		From 1 March 500
to 28 February 600		2 days
From 27 February 600
to 25 February 700		From 1 March 600
to 28 February 700		3 days
From 26 February 700
to 24 February 900		From 1 March 700
to 28 February 900		4 days
From 25 February 900
to 23 February 1000		From 1 March 900
to 28 February 1000		5 days
From 24 February 1000
to 22 February 1100		From 1 March 1000
to 28 February 1100		6 days
From 23 February 1100
to 21 February 1300		From 1 March 1100
to 28 February 1300		7 days
From 22 February 1300
to 20 February 1400		From 1 March 1300
to 28 February 1400		8 days
From 21 February 1400
to 19 February 1500		From 1 March 1400
to 28 February 1500		9 days
From 20 February 1500
to 4 October 1582		From 1 March 1500
to 14 October 1582		10 days
Julian RangeGregorian RangeDifference
From 5 October 1582
to 18 February 1700		From 15 October 1582
to 28 February 1700		10 days
From 19 February 1700
to 17 February 1800		From 1 March 1700
to 28 February 1800		11 days
From 18 February 1800
to 16 February 1900		From 1 March 1800
to 28 February 1900		12 days
From 17 February 1900
to 15 February 1923 [9] 		From 1 March 1900
to 28 February 1923		13 days
Orthodox [10] Julian RangeGregorian RangeJulian Behind By
From 16 February 1923
to 14 February 2100		From 1 March 1923
to 28 February 2100		13 days

See also

Related Research Articles

<i>Anno Domini</i> Western calendar era

The terms anno Domini (AD) and before Christ (BC) are used to label or number years in the Julian and Gregorian calendars. The term anno Domini is Medieval Latin and means "in the year of the Lord" but is often presented using "our Lord" instead of "the Lord", taken from the full original phrase "anno Domini nostri Jesu Christi", which translates to "in the year of our Lord Jesus Christ". The form "BC" is specific to English, and equivalent abbreviations are used in other languages: the Latin form, rarely used in English, is Ante Christum natum (ACN) or Ante Christum (AC).

Astronomical year numbering is based on AD/CE year numbering, but follows normal decimal integer numbering more strictly. Thus, it has a year 0; the years before that are designated with negative numbers and the years after that are designated with positive numbers. Astronomers use the Julian calendar for years before 1582, including the year 0, and the Gregorian calendar for years after 1582, as exemplified by Jacques Cassini (1740), Simon Newcomb (1898) and Fred Espenak (2007).

A calendar date is a reference to a particular day represented within a calendar system. The calendar date allows the specific day to be identified. The number of days between two dates may be calculated. For example, "25 November 2023" is ten days after "15 November 2023". The date of a particular event depends on the observed time zone. For example, the air attack on Pearl Harbor that began at 7:48 a.m. Hawaiian time on 7 December 1941 took place at 3:18 a.m. Japan Standard Time, 8 December in Japan.

<span class="mw-page-title-main">ISO 8601</span> International standards for dates and times

ISO 8601 is an international standard covering the worldwide exchange and communication of date and time-related data. It is maintained by the International Organization for Standardization (ISO) and was first published in 1988, with updates in 1991, 2000, 2004, and 2019, and an amendment in 2022. The standard provides a well-defined, unambiguous method of representing calendar dates and times in worldwide communications, especially to avoid misinterpreting numeric dates and times when such data is transferred between countries with different conventions for writing numeric dates and times.

The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year. The Julian calendar is still used in parts of the Eastern Orthodox Church and in parts of Oriental Orthodoxy as well as by the Amazigh people, whereas the Gregorian calendar is used in most parts of the world.

AD 1 or 1 CE is the epoch year for the Anno Domini (AD) Christian calendar era, and the 1st year of the 1st century and 1st millennium of the Christian and Common Era (CE). It was a common year starting on Saturday or Sunday, a common year starting on Saturday by the proleptic Julian calendar, and a common year starting on Monday by the proleptic Gregorian calendar.

The proleptic Julian calendar is produced by extending the Julian calendar backwards to dates preceding AD 8 when the quadrennial leap year stabilized. The leap years that were actually observed between the implementation of the Julian calendar in 45 BC and AD 8 were erratic.

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<span class="mw-page-title-main">Old Style and New Style dates</span> Changes in calendar conventions from Julian to Gregorian dates

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<span class="mw-page-title-main">Dual dating</span>

Dual dating is the practice, in historical materials, of indicating a date with what appear to be duplicate or excessive digits: these may be separated by a hyphen or a slash, or placed one above the other. The need for dual dating arose from the transition from an older calendar to a newer one. Another method used is to give the date of an event according to one calendar, followed in parentheses by the date of the same event in the other calendar, appending an indicator to each to specify which reference calendar applies.

The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull Inter gravissimas issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years differently so as to make the average calendar year 365.2425 days long, more closely approximating the 365.2422-day 'tropical' or 'solar' year that is determined by the Earth's revolution around the Sun.

<span class="mw-page-title-main">Conversion between Julian and Gregorian calendars</span>

The tables below list equivalent dates in the Julian and Gregorian calendars. Years are given in astronomical year numbering.

<span class="mw-page-title-main">Adoption of the Gregorian calendar</span> Transition to the "New Style" dating system

The adoption of the Gregorian Calendar was an event in the early modern history of most cultures and societies, marking a change from their traditional dating system to the modern dating system – the Gregorian calendar – that is widely used around the world today. Some states adopted the new calendar from 1582, some did not do so before the early twentieth century, others did so at various dates between. A few still have not, but except for these, the Gregorian calendar is now the world's civil calendar universally, although in many places an old style calendar remains used in religious or traditional contexts During – and for some time after – the change between systems, it has been common to use the terms "Old Style" and "New Style" when giving dates, to indicate which calendar was used to reckon them.

References

  1. ↑ "George Washington's Birthday". National Archives. n.d. Retrieved 11 May 2016.
  2. ↑ The proceedings of the Maya hieroglyphic workshop. University of Texas. 1982. p. 173.
  3. ↑ Spathaky, Mike. "Old Style New Style Dates and the Change to the Gregorian Calendar". GENUKI. Retrieved 27 May 2021. Increasingly parish registers, in addition to a new year heading after 24th March showing, for example '1733', had another heading at the end of the following December indicating '1733/4'. This showed where the New Style 1734 started even though the Old Style 1733 continued until 24th March. ... We as historians have no excuse for creating ambiguity and must keep to the notation described above in one of its forms. It is no good writing simply 20th January 1745, for a reader is left wondering whether we have used the Old or the New Style reckoning. The date should either be written 20th January 1745 O.S. (if indeed it was Old Style) or as 20th January 1745/6. The hyphen (1745-6) is best avoided as it can be interpreted as indicating a period of time
  4. ↑ Doggett, L. E. (1992). "Calendars". In P. Kenneth Seidelmann (ed.). Explanatory Supplement to the Astronomical Almanac. Sausalito, California: University Science Books. ISBN   0-935702-68-7. Archived from the original on 10 February 2012.
  5. ↑ "B.4. History of Units". PostgreSQL Documentation. 30 September 2021.
  6. ↑ "11.8. What Calendar Is Used By MySQL?". MySQL 5.0 Reference Manual. Retrieved 21 July 2010.
  7. ↑ "Date And Time Functions". SQL As Understood By SQLite. Retrieved 16 September 2010.
  8. ↑ "8.1.3. date Objects". Python v3.8.2 documentation.
  9. ↑ Greece was the last country to officially convert from the Julian calendar to the Gregorian calendar, so that 15 February 1923 was followed the next day by 1 March 1923.
  10. ↑ The Russian, Serbian, and Macedonian Orthodox churches still use the Julian calendar for calculating holy days such as Easter. [ citation needed ]
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