The proleptic Gregorian calendar is produced by extending the Gregorian calendar backward to dates preceding its official introduction in 1582.
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Usage [edit]
The proleptic Gregorian calendar is explicitly required for all dates before 1582 by ISO 8601:2004 (clause 4.3.2.1 The Gregorian calendar) if the partners to information exchange agree. It is also used by most Maya scholars,[1] especially when converting Long Count dates (1st century BC – 10th century). However, neither astronomers nor non-Maya historians generally use it.
For these calendars we can distinguish two systems of numbering years BC. Bede and later historians did not use the Latin zero, nulla, as a year (see Year zero), so 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 zero and represent earlier years as negative, 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 used in astronomical year numbering and in the international standard date system, ISO 8601. In these systems, the year 0 is a leap year.[2]
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 AD 1 until 1582 or later, so historians and astronomers prefer to use the actual Julian calendar during that period (see From Julian to Gregorian). But when seasonal dates are important, the proleptic Gregorian calendar is sometimes used, especially when discussing cultures that did not use the Julian calendar.
The proleptic Gregorian calendar is sometimes used in computer software to simplify the handling of older dates. For example, it is the calendar used by MySQL,[3] SQLite,[4] PHP, CIM, Delphi, Python[5] and COBOL.
Difference between Julian and proleptic Gregorian calendar dates [edit]
Before the introduction of the Gregorian calendar, the difference between Julian and proleptic Gregorian calendar dates were as follows: Whenever the calendars do not have corresponding days — such as the Julian leap day missing from the proleptic Gregorian calendar, or the ten days dropped when the Julian became the Gregorian calendar — the number of days that the calendars differ by is undefined around those dates.
The table below assumes a Julian leap day of 29 February, but the Julian leap day (the bissextile day) was ante diem bis sextum Kalendas Martias in Latin or 24 February (see Julian reform), so dates between 24 and 29 February in all leap years were irregular.
| Julian range | Proleptic Gregorian range | Gregorian ahead by: |
|---|---|---|
| From 3 March 1 BC (beginning of quadrennial leap years) to 28 February 100 |
From 1 March 1 BC to 26 February 100 |
−2 days |
| From 2 March 100 to 28 February 200 |
From 1 March 100 to 27 February 200 |
−1 days |
| From 1 March 200 to 28 February 300 |
From 1 March 200 to 28 February 300 |
0 days |
| From 1 March 300 to 27 February 500 |
From 2 March 300 to 28 February 500 |
1 day |
| From 1 March 500 to 26 February 600 |
From 3 March 500 to 28 February 600 |
2 days |
| From 1 March 600 to 25 February 700 |
From 4 March 600 to 28 February 700 |
3 days |
| From 1 March 700 to 24 February 900 |
From 5 March 700 to 28 February 900 |
4 days |
| From 1 March 900 to 23 February 1000 |
From 6 March 900 to 28 February 1000 |
5 days |
| From 1 March 1000 to 22 February 1100 |
From 7 March 1000 to 28 February 1100 |
6 days |
| From 1 March 1100 to 21 February 1300 |
From 8 March 1100 to 28 February 1300 |
7 days |
| From 1 March 1300 to 20 February 1400 |
From 9 March 1300 to 28 February 1400 |
8 days |
| From 1 March 1400 to 19 February 1500 |
From 10 March 1400 to 28 February 1500 |
9 days |
| From 1 March 1500 to 24 September 1582 |
From 11 March 1500 to 4 October 1582 |
10 days |
References [edit]
- ^ The proceedings of the Maya hieroglyphic workshop. University of Texas. 1992. p. 173.
- ^ Doggett, L. E. (1992). "Calendars". In P. Kennneth Seidelmann. Explanatory Supplement to the Astronomical Almanac. Sausalito, CA: University Science Books. ISBN 0-935702-68-7.
- ^ "11.8. What Calendar Is Used By MySQL?". MySQL 5.0 Reference Manual. Retrieved 21 July 2010.
- ^ "Date And Time Functions". SQL As Understood By SQLite. Retrieved 16 September 2010.
- ^ "8.1.3. date Objects". Python v2.7.2 documentation.
See also [edit]
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