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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.
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.
Its value is 0, 1, or 2 at different times of the year. Subtracting it leaves a small positive or negative fractional number of half turns, which is multiplied by 720, the number of minutes (12 hours) that the Earth takes to rotate one half turn relative to the Sun, to get the equation of time.
Doomsday rule. The Doomsday rule, Doomsday algorithm or Doomsday method is an algorithm of determination of the day of the week for a given date. It provides a perpetual calendar because the Gregorian calendar moves in cycles of 400 years. The algorithm for mental calculation was devised by John Conway in 1973, [ 1][ 2] drawing inspiration from ...
The rule estimates the expected date of delivery (EDD) by adding a year, subtracting three months, and adding seven days to the origin of gestational age. [13] [14] The result is approximately 280 days (40 weeks) from the start of the last menstrual period. Another method is by adding 9 months and 7 days to the first day of the last menstrual ...
February 30 or 30 February is a date that does not occur on the Gregorian calendar, where the month of February contains only 28 days, or 29 days in a leap year. However, from a historical perspective February 30 has been used at least once and appears in some reform calendars . The thirteenth-century scholar Johannes de Sacrobosco claimed that ...
The Rata Die method works by adding up the number of days d that has passed since a date of known day of the week D. The day of-the-week is then given by (D + d) mod 7, conforming to whatever convention was used to encode D. For example, the date of 13 August 2009 is 733632 days from 1 January AD 1. Taking the number mod 7 yields 4, hence a ...
The International Date Line around the antimeridian (180° longitude). The International Date Line ( IDL) is the line between the South and North Poles that is the boundary between one calendar day and the next. It passes through the Pacific Ocean, roughly following the 180.0° line of longitude and deviating to pass around some territories and ...