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Within these tables, January 1 is always the first day of the year. The Gregorian calendar did not exist before October 15, 1582. Gregorian dates before that are proleptic, that is, using the Gregorian rules to reckon backward from October 15, 1582.
A calendrical calculation is a calculation concerning calendar dates. Calendrical calculations can be considered an area of applied mathematics. Some examples of calendrical calculations: Converting a Julian or Gregorian calendar date to its Julian day number and vice versa (see § Julian day number calculation within that article for details).
[6] [d] (Scotland had already made this aspect of the changes, on 1 January 1600.) [7] [8] The second (in effect [e]) adopted the Gregorian calendar in place of the Julian calendar. Thus "New Style" can refer to the start-of-year adjustment, to the adoption of the Gregorian calendar, or to the combination of the two. It was through their use in ...
The authors design individual calendrical calculation algorithms for converting each of these calendars to and from a common format, the Rata Die system of days numbered from January 1 of the (fictional) Gregorian year 1. Combining these methods allows the conversion between any two of the calendars.
Zeller's congruence is an algorithm devised by Christian Zeller in the 19th century to calculate the day of the week for any Julian or Gregorian calendar date. It can be considered to be based on the conversion between Julian day and the calendar date.
The Gregorian calendar, like the Julian calendar, is a solar calendar with 12 months of 28–31 days each. The year in both calendars consists of 365 days, with a leap day being added to February in the leap years. The months and length of months in the Gregorian calendar are the same as for the Julian calendar.
The Lilian day number is a count of days of the Gregorian calendar and not defined relative to the Julian Date. It is an integer applied to a whole day; day 1 was October 15, 1582, which was the day the Gregorian calendar went into effect. The original paper defining it makes no mention of the time zone, and no mention of time-of-day. [25]
There are only four countries which have not adopted the Gregorian calendar for civil use: Ethiopia (Ethiopian calendar), Nepal (Vikram Samvat and Nepal Sambat), Iran (Solar Hijri calendar) [1] and Afghanistan (Lunar Hijri Calendar). [2] Thailand has adopted the Gregorian calendar for days and months, but uses its own era for years: the ...