Extension of the Gregorian calendar before its introduction
The proleptic Gregorian calendar extends the Gregorian calendar backward, proleptically, to dates before its 1582 introduction, creating a consistent dating system across history.
For example, when U.S. President George Washington was born on 11 February 1731,
Great Britain and its colonies still used the Julian calendar, also referred to as Old Style dating.
When Britain finally adopted the Gregorian calendar in September 1752, Washington's birth date became 22 February 1732.
During his life, both dates were observed and commemorated, but the latter is the one used and recognized since then.
[1][2]
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,[3] 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.[4]
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.[5]
Although the nominal Julian calendar began in 45 BC, leap years between 45 BC and 1 BC were irregular(see: 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).
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 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.
Julian range
Proleptic Gregorian range
Gregorian ahead by
From 3 March AD 4 (beginning of quadrennial leap years) to 1 March 100
^The proceedings of the Maya hieroglyphic workshop. University of Texas. 1982. p. 173.
^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
^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. [1]
^The Russian, Serbian, and Macedonian Orthodox churches still use the Julian calendar for calculating holy days such as Easter. [citation needed]
