The Gregorian calendar is the Calendrier currently used in the major part of the world. Conceived by a college of scientists under the direction of Christophorus Clavius to correct the secular drift of the Calendar Julien, his denomination bears the name of its instigator Gregoire {{Rom|XIII}}, Pope of 1572 with 1585. Its starting point, year 1, is an estimate of the birth of Jesus.

Structure of the calendar

The structure of the Gregorian calendar is similar to that of the Calendrier Julien of the ancient Rome into force hitherto. It is a solar calendar, being based on the revolution of the Earth around the Sun in 365,2422 Jour S of 24 metric hour S of 60 minute S of 60 second S. The Gregorian calendar gives an average time of the 365,2425 days year; to ensure an integer of days per year, one regularly adds to it (every 4 years in theory) a day bissextile , the February 29th ( to see Leap year ).

The complete cycle of the Gregorian calendar lasts 400 years: three centuries made up each of 24 cycles juliens (three 365 days years, then one 366 days year) follow-ups four years 365 days, then one century made up of 25 cycles juliens. The Gregorian calendar uses the rules of the Gregorian Comput.

Subdivisions

The Gregorian calendar is divided into twelve Mois, grouped into four Trimestre S:

One seven days period forms a Semaine. The one week days have each one a name: in French, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday and Sunday. One four weeks period forms a Mois, and a twelve months period forms a Année.

The era usually used with the Gregorian calendar is the Christian era, i.e. “after Jesus-Christ” ( Anno Domini in Latin, phrase still used in English and generally noted after the year in its form shortened AD , and formerly indicated in French like year of grace or year of the Lord ). There no was Année zero: the centuries and the millenia start with the year number one, in an ordinal way. Therefore, the 21e century and begin it on January 1st of year 1 of the third millennium, i.e. in 2001. Indeed a calendar is an account of the days and years: an account begins with one, not to zero. A measurement, as for it, starts to zero.

The era which precedes is the era pre-Christian woman ; she is deducted in opposed direction, there too as from the year “before Jesus-Christ” (although it is the year of its birth according to the Christian tradition), designation often shortened in French “front J. - C.”. The year 1 av. J. - C (sometimes also noted - wrongly - -1) corresponds to the year 0 UTC in the new astronomical calendar, which simplifies calculations of dates. It is the last year of II, and the last year of first century BC

Gregorian adjustment

the introduction of the Gregorian calendar to replace the Calendrier Julien began the October 15th 1582 with the countries claiming alignment on Rome: Spain, Portugal, States of the Italian peninsula (of which the Papal States). The goal was to fight against the drift of the date of Easter (Sunday after the first fictitious moon of the vernal equinox) which moved about the winter months.

In fact the principal and sufficient reform eliminating this drift (and which was applied easily in the other countries by the limited reform of the Julien calendar) was that of the mode of application of the leap years at the time of the last years of the century. The principal difference between the Gregorian calendar and its ancestor, the Calendar Julien not reformed, rests in the distribution of the leap years.

As noted above, the average Tropical year, i.e. the period of revolution of the Earth around the Sun, lasts 365,24219 days. While inserting one day bissextile every four years, the Julien calendar allotted to the year one 365,25 days intermediate duration. This induced a shift of approximately 8 days per millenium compared to true time, with for effect that the date of Easter (determined by the equinox of spring) slipped gradually to approach February (instead of remaining located, according to lunations, between Sunday preceding the last week by March and that finishing the third week of April).

One thus considers as common years (365 days years) the years which are multiple 100 without being multiple 400. Thus 1600 and 2000 were bissextile, but not 1700,1800,1900 which was common . In the same way, 2100,2200,2300 will be common, whereas 2400 is a Leap year.

While observing this rule, one arrives at one 365,2425 days year instead of 365,24219 days is a three days excess in 10.000 years. It was proposed to amend the rule to regard the multiple years of 4.000 as normals. But because of the shortening of the evaluated tropical year with 0,5 S per century and of the lengthening of the day of 1,64 milliseconds per century, it is illusory to arrive at this level of precision, uncertainties over the duration of the year in 10.000 years being of the same order of magnitude.

Introduction of calendar Gregorian includes/understands also second reform of application more delicate, shift Gregorian which removed ten days of the calendar, between the October 4th 1582 and the October 15th 1582 for the countries having immediately followed Rome, which made it possible to fix again the vernal equinox on March 21st, as it was the case at the beginning of the Christian era.

These ten days made it possible to make up for of a blow increasing lost time taken by the old Julien calendar on the dates of the equinoxes since the beginning of the Christian era, i.e. more than 15 centuries front, and thus with 12 leap years in excess (in 100,200,300,500,600,700,900,1000,1100,1300,1400 and 1500 following new rules of calculation) if the Julien calendar had been stable over all this period until 1582, but of the former corrections had already been applied during this period while omitting to add one day at the end of February certain years which should have been bissextile (according to the old rule of the Julien calendar).

However, certain countries were also long in applying the Gregorian adjustment of the last years of the century (dates of adjustment according to the countries), and thus counted the year 1700 like bissextile (according to the old Julien calendar not reformed), which increased the lag of date to eleven days. Sweden which used the Julien calendar tried first once to observe only the rule of Gregorian adjustment in 1700 (nonbissextile), without applying the 10 days shift, then began again itself in 1704 by adding two days to February (doubly bissextile year) to return to the old Julien calendar still used in England or in the Protestant and orthodoxe countries close.

The Sweden and the England will apply the Gregorian calendar completely only later, under the influence of the Germany, the Netherlands and the Suisse whose States used simultaneously the calendars Julien and Gregorian according to whether they were of confession Protestant or catholic, and who during their unification wanted to standardize the calendars.

The third reform of the Gregorian calendar was to number the years as from January and not March as in the Julien calendar (the beginning of the year in the Julien calendar varied itself - to see the external article corresponding and its bonds). This reform made it possible to make coincide the pagan festivals of the new year in the time of Christmas, and not little before the holy period of Easter. In many country, this last reform was applied years or even several centuries after that of the adjustment and the Gregorian shift. However it will not be the case of the orthodoxe countries, of which the year began in September.

Introduction of the Gregorian calendar

Proposed at the beginning of the reign of Gregoire, and supported by England in a ecumenical Council, this calendar takes its name when the pope decides to adopt it too. Initially refused in many countries for religious or political reasons (conflict between the Papauté and certain countries Protesting S, and application limited by the orthodoxe Churches which accepts the novel mode of calculation of the last years of the century in the Julien calendar but without applying the calendar shift) the Gregorian calendar was diffused slowly:

The countries which use the Gregorian calendar associated with another calendar are:

Only the Saudi Arabia, the Iran, the Afghanistan, the Pakistan, the Ethiopia, and the Vietnam do not use the Gregorian calendar.

DEBATEs on the Gregorian calendar in the History

If the principle of the Gregorian adjustment were not called into question, it is not the same of its internal structure.

Criticisms related of course in France to its bonds with the Christianisme, through the Christian era, of religious holidays, and of the references to the Saint S in the Agenda S. the diaries were indeed at the time one of the principal information means in the French campaigns.

That justified some projects of laic calendars such as for example the republican Calendrier of the French revolution. To the difference of the Metric system, this one does not lead: it is true that the principle of resting more that one day out of ten ( decadi ) instead of seven could not fill with enthusiasm. Another reason, more technical, was that the shift of calendar between France and the countries bordering raised certain difficulties in the border zones.

Another project of calendar Laïc (the Calendrier fixes) was proposed by Auguste Count: the calendar positivist. This one was practically not used apart from Count and of some disciples.

Others critical seem to relate to construction even calendar:

  • variable month length (from 28 to 31 days) which complicates for example the analysis of the economic statistics;
  • difficult correspondence enters the name of the days and their number the month;
  • lasted of the quarters (second quarters being for example shorter than the third);
  • many weeks (4,33) per month;
  • variation of the date of certain bank holidays like Easter.

But these originalities are not related to the human choices, the calendar simply tries to follow the astronomic year. It does not comprise an integer of days and the periods estival and winter have 7 days of variation of duration. The lunar cycle is not fixed him either. Nevertheless one needs well a number of whole days in one year to find and follow the duration of the days there (to raise Sun).

This difficulty led many reform proposals to use the principle of the Jour epagomene. It is about one day white which does not enter the calculation of the week. While adding one (or two leap years) epagomenes day to the year, one manages to obtain the equality 365 = 7×52 + 1. One finds the same idea with the complementary days in the republican Calendrier of the French revolution.

The duration of the months had been selected in order to correspond roughly to a lunar cycle. Thus, even a population not well-read woman could know about, by observing the change of aspect of the moon, when one month had been passed; the reference to the moon was important for the sailors (to know the Marée S) and for the farmers (night works in the fields) of a population very mainly rural.

So today this bond is not obvious in our urban civilization , one can note that the large majority of the reforms of the calendar tries to preserve one month of approximately a lunation. It is however necessary to note the emergence of the Calendrier badi `, used in the Bahaïsme. If it is also based over a solar year, this one beginning with the equinox from spring the March 21st, its originality is due to the abandonment of the lunar reference for the duration of the month. One year of this calendar indeed comprises 19 19 days month (either 361 days). The 4 or 5 days additional necessary to supplement one year are inserted between 18th and the 19th month, and are named the intercalary days .

During last three centuries, other reform proposals were advanced. Most known were the proposals of universal Calendrier and of Calendrier fixes. About the middle of the 20th century, the Société of the Nations then the United Nations undertook studies to reform the calendar. Those were abandoned under the pressure of country like the the United States, the the United Kingdom, the Netherlands or the Indonesia, officially not to disorganize the religious traditions.

Many authors of Science-fiction played with the idea that the land calendar would be perhaps a day used in all space known, whereas everyone or almost would have forgotten its initial raison d'être, even the existence of the Earth itself.

From a point of view plus ground with ground, to the approach of the year 2000, when it was a question of adapting the systems Informatique S which, for the majority, were assigned by the Bogue of the year 2000, via the date system and the algorithms of Datation employed in the computer programs, the question arose between the authorities of different Religion S, of knowing which calendar was the reference. At the conclusion of a debate held in the United States, it was finally decided to preserve, by preoccupation with a simplification, the Gregorian calendar…

Use by the historians

Before 1582, one used the Calendrier Julien. It is this calendar which thus also the historians for this period use, since they work with the dates related to the documents. The Gregorian calendar is thus seldom used in a retroactive way.

Anecdotes

  • Therese d' Avila dies in the night of the 14 to the October 15th 1582. The date of the festival of the saints being fixed the shortly after their death (their " birth with the ciel"), the festival of this holy falls on October 15th.

  • Shakespeare and Cervantès died at the same date… but not the same day, the United Kingdom - for its part Anglican - not having immediately adopted the Gregorian calendar.

  • Montaigne, in its Tests , mentions the difficulties which its contemporaries tested to gradually pass to the new calendar.

  • Of the vestiges of the Julien calendar remains fossilized in the layers of the Popular culture. They are exhumed regularly at the time of the publication of the various diaries, agricultural almanacs and other publications of gardening. Examples:

    • " In Holy Luce, the days lengthen jump of a chip,
      With Nadal       (Christmas) of the foot of Gall (cock)
      And with the new year of the step of an ox. "
      These dates are those of the Julien calendar. In our current calendar we celebrate Holy Luce on December 13rd but the days start to lengthen only on December 22nd.
    • " the Saint Barnabe (June 11th) is the longest day of the year. "
      This saying testifies today the 10 days of the shift introduced during the adoption of the Gregorian calendar to make up for lost time of the Julien calendar on Soleil.
    • " With the Saint Matthieu (on September 21st) , day equal to the neut. " stress him to it advent of the autumnal equinox in conformity with the calendar in force.
    • " With the Holy-Catherine (November 25th), all takes root! " Excel reference mark for the gardeners in order to make the majority of the plantations.

See too

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