Everlasting calendar

A perpetual Calendrier indicates the day of the week for any date, whatever the year - in opposition to a traditional calendar which is limited to a year given.

The everlasting calendar Moret consists of a series of three tables in which one chooses successively the century, the year, the month and the day of the month (day of the month). One obtains a number from 1 to 7 which corresponds to the day of the semaine.

Version by tables

Directions for use

  1. To find in table 1 the figure with the intersection of the hundreds (years) and the year. (One calls this figure: A)

  2. Trouver in table 2 the figure with the intersection of the line of has and the column of the month. (One calls this figure: B)

  3. To find in table 3 the day with the intersection of the line of B and the date recherchée.


Table 1: years and years



Table 2: month



Table 3: days



Memorable version

The method suggested below is a memorable version of the Moret calendar: it removes or simplifies the tables by calling upon logic and mental calculation.

This method allots a number to the century, at the year, in the month and the day of the month. By adding the four numbers, one obtains the day of the week. One can also use this method to make calculations opposite: which are the months which contain one Friday the 13th? in how much years will find one the same dates?

All these numbers are definite modulo 7, i.e. 5 is equivalent to 12,19,26… The end result of the addition gives the day of the week, by giving to Monday figure 1. An end result of 12 or -2 will thus correspond for example to 5, i.e. Friday.

Secular number

The secular number is the same one for every year starting with the two same figures. One thus attaches here year 2000 to the years 2001 to 2099 although it does not form formally part of the 21e century. Calculation is different in the Julien calendar and the Gregorian calendar (for the dates of passage of the Julien calendar to the Gregorian calendar apart from France, see Passage to the Gregorian calendar).

  • Calendar Julien (until the December 9th 1582 in France). The secular number is equal to: 19 - the first two figures of the année.

Example: for the years 1200 to 1299, the secular number is 19 - 12 = 7

1582 to 1599: 1
1600 to 1699: 0
1700 to 1799: 5
1800 to 1899: 3
1900 to 1999: 1
2000 to 2099: 0
2100 to 2199: 5

Remark : this number falls by two units each century, except when the first two figures are a multiple of 4 (1600 to 1699,2000 to 2099).

Annual number

The following table gives the years for which the annual number is equal to 0. As from these years, the annual number increases by a unit each year, and two if the year is bissextile. If one does not wish to learn this table by heart, one can note that these years are found every 28 years (7 days of week X 4 years between two bissextile).

Années the annual number is 0:

Example: the year 2010 has an annual number of 0 and the year 2016 has an annual number of 8 because the leap years should be counted 2012 and 2016.

One can as notice as the result is given by the following formula: for the year has , one calculates the Euclidean Division of has by 4 (i.e. the number C when one writes a=4c+r , with R smaller than 4), and the annual number is then given by the remainder of the Euclidean division of a+c-5 by 7. In the preceding examples, one finds: a=10 , therefore c=2 then a+c-5=7 whose remainder in division by 7 is well 0; and for the second: a=16 , therefore c=4 , then a+c-5=15 whose remainder in division by 7 is 1; who is quite equivalent to 8 modulos 7.

Remark : if two years have the same amount secular number + annual number , a calendar of the Stations used the first year will be also valid for the other, except if one and only one of these two years are bissextile.

Monthly number

The following table gives the monthly number for each month of the year:

Example: January has a monthly number of 4 in 2003 and 3 in 2004 (leap year).

Day of the month

The last figure is the day of the month itself, i.e. the number of the day in the month.

Examples

See too

External bonds

  • virtual Calendar: virtual calendar used in France.
  • Calendar in line calendar, school vacations, éphéméride, lunar cycle, diary, alarm system, etc
  • Everlasting calendar and school vacations: everlasting calendar, bank holidays and French school vacations by zones
  • universal Everlasting calendar: everlasting calendar and lunations for 36 countries + calendar Julien
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