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The Julian date (JD) of any instant is the Julian day number plus the fraction of a day since the preceding noon in Universal Time. Julian dates are expressed as a Julian day number with a decimal fraction added. [8] For example, the Julian Date for 00:30:00.0 UT January 1, 2013, is 2 456 293.520 833. [9]
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
Simply count 11 days from the Gregorian date, treated as zero, toward the left (subtract) to find the equivalent Julian date. The count remains the same as early as March 1 Gregorian. Going from the Julian to the Gregorian we count 11 days to the right (add), but the earliest Julian date in 1700 is February 19.
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 calendar).
J transit is the Julian date for the local true solar transit (or solar noon). 2451545.0 is noon of the equivalent Julian year reference. 0.0053 sin M − 0.0069 sin ( 2 λ ) {\displaystyle 0.0053\sin M-0.0069\sin \left(2\lambda \right)} is a simplified version of the equation of time .
The range of days considered for the full moon to determine Easter are 21 March (the day of the ecclesiastical equinox of spring) to 18 April—a 29-day range. However, in the mod 30 arithmetic of variable d and constant M , both of which can have integer values in the range 0 to 29, the range is 30.
The overall function, , normalizes the result to reside in the range of 0 to 6, which yields the index of the correct day of the week for the date being analyzed. The reason that the formula differs between calendars is that the Julian calendar does not have a separate rule for leap centuries and is offset from the Gregorian calendar by a fixed ...
The Gregorian calendar was implemented in Russia on 14 February 1918 by dropping the Julian dates of 1–13 February 1918, [h] pursuant to a Sovnarkom decree signed 24 January 1918 (Julian) by Vladimir Lenin. The decree required that the Julian date was to be written in parentheses after the Gregorian date, until 1 July 1918. [19]