You are at the section Calendar History
Calendar 10:The Gregorian Calendar
Gregorian Calendar (Number Change Day on January 1)
- The Gregorian Calendar is also known as the Gregorian-Christian calendar, based on the same reckoning year the Julian-1 calendar's founders believed when Jesus Christ was conceived.
- The Gregorian Calendar was offset from the Julian-1 calendar by 10 days in 1582 instead of 13.
- Pope Gregory XIII's goal was to put Easter back where it belonged. He corrected, not to when the Julian calendar began, but to when the date of Easter was first adopted, which was at the council of Nicaea on July 4, 325 A.D., a 25 years after the century the early Church first introduced Easter for celebration.
- The motivation for the adjustment was to bring the date for the celebration of Easter to the time of year in which it was celebrated when it was introduced by the early Church.
- From that date range establishment, the calculations of Easter during the Gregorian calendar both current and proleptic can be determined. For the proleptic Gregorian Easter dates of 1582 and before, they would have been the correct dates used had the Julian-1 calendar had not drifted forward in time, resulting in a 10 day error by 1582, making many Easter dates fall into the early April to mid May date range in real Gregorian dating.
- For the proleptic range of the Gregorian Calendar going backwards before the date it was first implements, the Gregorian calendar matches up with the Julian-1 calendar in the third century between March 1, 200 AD and February 28, 300 AD.
- The calendar restored the Spring Equinox to the average March 21 date (in some parts of Earth, it may be March 19, 20, 22 or 23 depending on year)
- There is no year zero, but for calculation purposes, all of the B.C. years are incremented by one year (ex: 1 B.C. + 1 = 0, 2 B.C. + 1 = -1, etc) for purposes of mathematical comparisions with converted dates of other calendars and the Julian Date calendar.
- Oct 15, 1582 was first day of the Gregorian Calendar (Oct 5, 1582 Julian-1 calendar date)
- The last day of the first year of its existenance was Dec 31, 1582, with the change of the year moved to January 1, starting the year 1583.
- Most Western European countries changed the start of the year to 1 January before they adopted the Gregorian calendar.
- Leap Year Days
- Leap Year Days were on every year divisible by four, except for the years that are divisible by 100 but not in turn divisible by 400
- 1600 and 2000 were leap years. 1700, 1800, 1900 were not leap years. 2100, 2200, 2300 are not going to be leap years. 2400 will be a leap year.
- Conversions from Julian to Gregorian Dates (Assuming that Jan 1 is the Near Year on the Julian-1 Calendar:)
- From 15 October 1582 to 28 February 1700 = From 5 October 1582 to 18 February 1700==10 days
- From 1 March 1700 to 28 February 1800==From 19 February 1700 to 17 February 1800==11 days
- From 1 March 1800 to 28 February 1900==From 18 February 1800 to 16 February 1900==12 days
- From 1 March 1900 to 28 February 2100==From 17 February 1900 to 15 February 2100==13 days
- From 1 March 2100 to 28 February 2200==From 16 February 2100 to 14 February 2200==14 days
- Leap Year Date Comparisons
- Leap Years on the Julian-3-25- Calendar were on year numbers that were one less than an exact multiple of four. This was in order for the dates between the Julian-3-25- and Julian-1 calendars to be synched up.
- Julian-3-25- dates existed as leap year days:
- Feb 29, 1659 (maps to Feb 29, 1660 Julian-1) or simply date as Feb 29, 1659/60
- Feb 29, 1643 (maps to Feb 29, 1644 Julian-1) or simply date as Feb 29, 1643/4
- Feb 29, 1647 (maps to Feb 29, 1648 Julian-1) or simply date as Feb 29, 1647/8
Julian Calendars from the 15th Century Forward, Gregorian Calendars
- Dates on the Calendar.
- Sometime during the Medieval Era, the way the Romans numbered the months were replaced with the method of simply giving each day a number, counting up from the first day of the month, which is a "1", and counting up until the end of the month is reached.
- The Day Numbering scheme changed from the Kalends method (counting down inclusively to the first of the following month), to the Counting Up method (days since the last day of the previous month) sometime during the Medieval Era.
- There were no more divisions of months (Kalends, Nonaes, Ides); instead, the months were treated as a whole.
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