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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]
The number of days between two dates, which is simply the difference in their Julian day numbers. The dates of moveable holidays, like Christian Easter (the calculation is known as Computus) followed up by Ascension Thursday and Pentecost or Advent Sundays, or the Jewish Passover, for a given year. Converting a date between different calendars.
Date of Easter. A calendar of the dates of Easter, for the 95 years 532–626, marble, in the Museum of Ravenna Cathedral, Italy. Five 19-year cycles are represented as concentric circles. Dates are given using the system of the Roman calendar, as well as the day of the lunar month. As a moveable feast, [1] [2] the date of Easter is determined ...
The doomsday's anchor day calculation is effectively calculating the number of days between any given date in the base year and the same date in the current year, then taking the remainder modulo 7. When both dates come after the leap day (if any), the difference is just 365y + y / 4 (rounded down). But 365 equals 52 × 7 + 1, so after taking ...
When the apparent solar time that corresponds to a given civil time is to be found, the difference in longitude between the site of interest and the time zone meridian, daylight saving time, and the equation of time must all be considered. Calculation. The equation of time is obtained from a published table, or a graph. For dates in the past ...
On average, the astronomical solstices and the equinoxes advance by 10.8 minutes per year against the Julian year. As a result, 21 March (which is the base date for calculating the date of Easter) gradually moved out of alignment with the March equinox. This is a visual example of the official date change from the Julian calendar to the Gregorian.
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 number from the "Difference" column.
The basic approach of nearly all of the methods to calculate the day of the week begins by starting from an "anchor date": a known pair (such as 1 January 1800 as a Wednesday), determining the number of days between the known day and the day that you are trying to determine, and using arithmetic modulo 7 to find a new numerical day of the week.