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No guidance is provided about conversion of dates before March 5, -500, or after February 29, 2100 (both being Julian dates). For unlisted dates, find the date in the table closest to, but earlier than, the date to be converted. Be sure to use the correct column. If converting from Julian to Gregorian, add the
The need to correct the calendar arose from the realisation that the correct figure for the number of days in a year is not 365.25 (365 days 6 hours) as assumed by the Julian calendar but slightly less (c. 365.242 days). The Julian calendar therefore has too many leap years.
To avoid confusion and further mistakes, the Julian calendar was restored in 1712 by adding an extra leap day, thus giving that year the only known actual use of February 30 in a calendar. That day corresponded to February 29 in the Julian calendar and to March 11 in the Gregorian calendar.
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).
The term Julian date may also refer, outside of astronomy, to the day-of-year number (more properly, the ordinal date) in the Gregorian calendar, especially in computer programming, the military and the food industry, [10] or it may refer to dates in the Julian calendar. For example, if a given "Julian date" is "October 5, 1582", this means ...
The Julian JDN column is Julian day number when the date is interpreted as a Julian date, and the Gregorian JDN column is the JDN when the date is interpreted as Gregorian date. The calculations were done in Excel; JDN was calculated using algorithms from chapter 12 of Seidelman's (1992) Explanatory Supplement to the Astronomical Almanac ...
Simple formulae for Julian day numbers and calendar dates. Quarterly Journal of the Royal Astronomical Society, 25, 53. ...
Gregory's calendar reform modified the Julian rule, to reduce the average length of the calendar year from 365.25 days to 365.2425 days and thus corrected the Julian calendar's drift against the solar year: the Gregorian calendar gains just 0.1 day over 400 years. For any given event during the years from 1901 through 2099, its date according ...