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Proleptic Gregorian calendar

{{short description|Extension of the Gregorian calendar before its introduction}}

{{Use dmy dates|date=May 2021}}

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 day of U.S. President George Washington's birth 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 instead of 1 January (e.g. 31 December 1700 was followed by 1 January 1700, and 24 March 1700 was followed by 25 March 1701). After Great Britain switched to the Gregorian calendar, Washington's birth was dated 22 February 1732 proleptically, according to the Gregorian calendar applied backward. This remains the modern dating of his birth.{{Cite web| title = George Washington's Birthday| work = National Archives| access-date = 11 May 2016| url = https://www.archives.gov/legislative/features/washington/| date = n.d.}}

Usage

ISO 8601:2004 (clause 3.2.1 The Gregorian calendar) allows use of the proleptic Gregorian calendar for dates before its introduction only if the parties to the communication agree. Most scholars of the Maya civilization also use it,{{cite book |title=The proceedings of the Maya hieroglyphic workshop |date= 1982|publisher= University of Texas |page= 173 }} 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.{{cite web | first=Mike | last=Spathaky | url=http://www.cree.name/genuki/dates.htm | title=Old Style New Style Dates and the Change to the Gregorian Calendar | quote=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 | publisher=GENUKI | accessdate=27 May 2021 }}

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.

{{cite book| url = http://charon.nmsu.edu/~lhuber/leaphist.html| chapter = Calendars| title = Explanatory Supplement to the Astronomical Almanac| publisher = University Science Books| editor = P. Kenneth Seidelmann| last1 = Doggett| first1 = L. E.| date = 1992| isbn = 0-935702-68-7| location = Sausalito, California| url-status = dead| archive-url = https://web.archive.org/web/20120210184836/http://charon.nmsu.edu/~lhuber/leaphist.html| archive-date = 2012-02-10}}

Although the nominal Julian calendar began in 45 BC, leap years between 45 BC and 1 BC were irregular{{xref|(see: {{slink|Julian calendar|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,{{cite web |url=https://www.postgresql.org/docs/current/static/datetime-units-history.html#DATETIME-UNITS-HISTORY|title=B.4. History of Units |work=PostgreSQL Documentation |date=30 September 2021 }} MySQL,

{{cite web |url= http://dev.mysql.com/doc/refman/5.0/en/mysql-calendar.html|title= 11.8. What Calendar Is Used By MySQL?|access-date=21 July 2010 |work= MySQL 5.0 Reference Manual}} SQLite,

{{cite web |url= http://www.sqlite.org/lang_datefunc.html|title= Date And Time Functions|access-date=16 September 2010 |work= SQL As Understood By SQLite}} PHP, CIM, Delphi and Python.{{cite web |url=https://docs.python.org/library/datetime.html#date-objects|title=8.1.3. date Objects |work=Python v3.8.2 documentation }}

Julian calendar differences

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 ({{lang|la|ante diem bis sextum Kalendas Martias}} in Latin) was accomplished by repeating 24 February {{xref|(see: {{slink|Julian calendar|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, 29 February is included in the calculation when the conversion crosses the border of February and March.

class="wikitable"

! Julian range

! Proleptic Gregorian range

! Gregorian 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 range

! Gregorian range

! Difference

From {{date|1582/10/5}}
to {{date|1700/2/18}}

|From {{date|1582/10/15}}
to {{date|1700/2/28}}

|10 days

From {{date|1700/2/19}}
to {{date|1800/2/17}}

|From {{date|1700/3/1}}
to {{date|1800/2/28}}

|11 days

From {{date|1800/2/18}}
to {{date|1900/2/16}}

|From {{date|1800/3/1}}
to {{date|1900/2/28}}

|12 days

From {{date|1900/2/17}}
to {{date|1923/2/15}}Greece was the last country to officially convert from the Julian calendar to the Gregorian calendar, so that {{date|1923/02/15}} was followed the next day by {{date|1923/03/01}}. [https://www.timeanddate.com/calendar/?country=11&year=1923]

|From {{date|1900/3/1}}
to {{date|1923/2/28}}

|13 days

OrthodoxThe Russian, Serbian, and Macedonian Orthodox churches still use the Julian calendar for calculating holy days such as Easter. {{citation-needed|date=November 2023}} Julian range

! Gregorian range

! Julian behind by

From {{date|1923/2/16}}
to {{date|2100/2/14}}

|From {{date|1923/3/1}}
to {{date|2100/2/28}}

|13 days

See also

References

{{Reflist}}

{{Chronology}}{{Calendars}}

Category:Gregorian calendar

Category:Specific calendars