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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
Julian calendar: Gregorian minus 13 days: ... A mean calendar year is 365 + 97 / 400 days = 365.2425 days, or 365 days, 5 hours, ... Conversion from Julian to ...
Note that Julian days begin at noon (hour = 12) and thus hours 0–11 of a solar day are one Julian day earlier than hours 12–23. The value may extend outside of the normal range and is considered as additional number of julian days (a Julian day is 24 hours or 86400 seconds exactly, ignoring any adjustment of leap seconds within the UTC ...
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).
In other words, the Julian calendar gains 3.1 days every 400 years. 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 ...
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]
The first form of R.D. is a continuously-increasing fractional number, taking integer values at midnight local time. It is defined as: RD = JD − 1,721,424.5. Midnight local time on December 31, year 0 (1 BC) in the proleptic Gregorian calendar corresponds to Julian Date 1,721,424.5 and hence RD 0.
Thus the calendar mean year is 365 + 218 ⁄ 900 days, but this is actually a double-cycle that reduces to 365 + 109 ⁄ 450 = 365.24 2 days, or exactly 365 days 5 hours 48 minutes 48 seconds, which is exactly 24 seconds shorter than the Gregorian mean year of 365.2425 days, so in the long term on average the Revised Julian calendar pulls ahead ...