Proleptic Gregorian calendar
From Wikipedia, the free encyclopedia
The proleptic Gregorian calendar is produced by extending the Gregorian calendar to dates preceding its official introduction in 1582.
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, 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. 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.
Note that the Julian calendar was in actual use from AD 1 ubtil 1582 or later (see From Julian to Gregorian), so historians and astronomers prefer to use the actual Julian calendar during that period. Likewise, the proleptic Julian calendar is used to specify dates before AD 1, the first common year that did not follow a quadrennial leap year (leap years between 45 BC and 1 BC were irregular, see Leap year error). But when seasonal dates are important, the proleptic Gregorian calendar is sometimes used, especially when discussing cultures that did not use the Julian calendar.
[edit] Difference between Julian and proleptic Gregorian calendar dates
Before the introduction of the Gregorian calendar, the difference between Julian and proleptic Gregorian calendar dates has increased as follows:
| Julian range | Proleptic Gregorian range | Difference |
|---|---|---|
| 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 |
