Gregorian Calendar

The Gregorian calendar is the calendar used in most parts of the world ^{Structure of the Gregorian calendar}

The Gregorian calendar is similar to the Julian calendar of ancient Rome in force until then. It is a solar calendar based on the revolution of Earth around the Sun in 365.24221935 days of 24 hours. The Gregorian calendar gives an average time of the year of 365.2425 days. To ensure a whole number of days in the year, we add every 4 years (years with a vintage divible by 4) a leap day on February 29 (see leap year ), except that century years are leap if their vintage is divible by 400 (thus 1600 and 2000 were leap years, 1700, 1800 and 1900 have not been, 2100, 2200 and 2300 are not leap years, 2400 will be ... etc.. ). He is currently an error of about one day 3000 years instead of one day of 129 years with the Julian calendar.

The Gregorian calendar uses the rules of the Gregorian.

Subdivisions

The Gregorian calendar is divided into twelve months , grouped into four quarters :

1st Quarter	2nd Quarter	Quarter 3	4th Quarter
January , 31 days February , 28 or 29 days March , 31 days	April , 30 days May , 31 days June , 30 days	July , 31 days August , 31 days September , 30 days	October , 31 days November , 30 days December , 31 days
90 or 91 days	91 days	92 days	92 days

A seven-day period as a week. The days of a week have a name: in French, Sunday , Monday , Tuesday , Wednesday , Thursday , Friday and Saturday. A period of 28, 29, 30 or 31 days (approximately 4.35 weeks) forms a month , and a period of twelve months form a year.

The era commonly used with the Gregorian calendar is the Christian era , that is to say, "AD" ( Anno Domini in Latin phrase still used in English and most often noted after the year in its abbreviated AD French and formerly designated as "AD" or "year of the Lord").

The age is above the pre-Christian era and is counted in the opposite direction, again from time zero. It is in the direction "before Christ", often abbreviated in French as "Ave. AD. The years "x ave. AD are often rated negatively.

The Gregorian Adjustment

The introduction of the Gregorian calendar began to replace the 15 October 1582 in the countries claiming alignment with Rome: Spain , Portugal , United States of the Italian peninsula (including the Papal States ). The aim was to fight against the drift of the date of Easter (the Sunday after the first moon dummy of the vernal equinox), which was moving towards the summer.

In fact, the major reform and sufficient eliminating this drift (which was easily applied in other countries by the limited reform of the Julian calendar) was the mode of application of leap years during centennial year. The main difference between the Gregorian calendar and its predecessor, the Julian calendar unreformed, lies in the distribution of leap years.

The tropical year average of 365.24219 days. By inserting a leap day every four years, attributed to the Julian calendar year an average of 365.25 days. This induces a lag of about 8 days per thousand compared to real time, with the effect that the date of Easter determined by March 21 (sort of equinox spring legal), gradually slipped away from the actual vernal equinox, and that he "went back" on the calendar so slowly, reaching around 10 March (Julian) to the ^sixteenth century.

It looked like so common years (years of 365 days) vintages that are multiples of 100 without multiple of 400. Thus 1600 and 2000 were leap years but not 1700, 1800, 1900, which were common. Similarly, 2100, 2200, 2300 will be common, while 2400 will be a leap year.

Applying this rule, we arrive at a year of 365.2425 days instead of 365.24219 days is an excess of three days in 10,000 years. It was proposed to amend the rule to consider the multiple years of 4000 to be normal. But because of the shortening of the tropical year estimated at 0.5 sec per century and elongation of the day of 1.64 milliseconds per century, it is unrealistic to achieve this level of accuracy, uncertainty over the duration year in 10 000 years of the same order of magnitude.

The introduction of the Gregorian calendar also includes a second reform implementation more difficult, offset Gregorian suppressed ten calendar days, between 4 October 1582 and 15 October 1582 for the countries that immediately followed Rome, which allowed to fix again the spring equinox on March 21, as was the case at the beginning of the Christian era, the First Council of Nicaea in 325.

These ten days allowed to catch a shot taken by the growing delay the Julian calendar the dates of the equinoxes since the beginning of the Christian era, more than 12 centuries before, and find the correlation between the equinox March 21 spring calendar. 9 years leap were counted too much (500, 600, 700, 900, 1000, 1100, 1300, 1400 and 1500 under the new calculation rules) if the Julian calendar did not induce this shift for the entire period until 'in 1582, but previous corrections had been applied during this period by failing to add a day in late February in some years that should have been leap (following the old rule of the Julian calendar).

However, some countries have been slow to implement the adjustment of the Gregorian century years, and therefore counted as the leap year 1700 (according to the unreformed Julian calendar), which increased the lag time in eleven days. Sweden, which used the Julian calendar was first attempted to apply only the Gregorian adjustment rule in 1700 (non-leap), without applying the offset of 10 days and then rebounded in 1712 by adding two days in February (leap year doubling) to return to the old Julian calendar still used in England and in Protestant and Orthodox neighbors.

The Sweden and England will implement fully the Gregorian calendar later, under the influence of Germany , the Netherlands and Switzerland in which states used simultaneously Julian and Gregorian calendars after they were Protestant or Catholic, and when they wanted unification uniform schedules.

The third reform of the Gregorian calendar was starting the year in January instead of March as the month before (the start of the year in the Julian calendar itself has changed - see the article and external links). This reform helps to match the pagan holidays of New Year in time for Christmas, not before the holy time of Easter. In many countries, this reform has been implemented for years or even several centuries after the adjustment and offset Gregorian. However, this has not been the case with Orthodox countries, including the year began in September.

Introduction of the Gregorian calendar

Proposed early in the pontificate of Gregory XIII and supported by England in an Ecumenical Council , the calendar takes its name when the Pope decides to adopt it by the Bull Inter extremely serious. First, in many countries refused on religious grounds or political (conflict between the papacy and some countries Protestants , and limited application by Orthodox Churches that accept the new method of calculating the secular years in the Julian calendar but without applying the offset calendar), the Gregorian calendar was released slowly

• in October 1582 in Italy , in Portugal , in its Brazilian colony and Spain ;
• in late 1582 in France , in Austria and Poland ;
• in the years 1582 to 1584 in the Spanish colonies in Latin America and into California , and the Philippines ;
• the ^sixteenth century to the ^eighteenth century in the French colony of Canada ;
• in the years 1583 ( electorate of Mainz ) in 1590 in continental Europe and central non- Lutheran ;
• in 1600 in Scotland ,
• in 1610 in northern Poland ,
• in 1648 (when the Treaty of Westphalia ) in Alsace ,
• in 1700 in Iceland and Greenland in Germany
• in 1752 the United Kingdom and its colonies on the east coast of North America, and is now north-western United States ,
• in 1753 in Sweden ,
• in the late ^eighteenth century in Australia ,
• in 1872 in Albania ,
• in 1873 in Japan ,
• in 1895 in Korea ,
• in 1912 in Taiwan ,
• in 1915 in Lithuania and Estonia ,
• in 1916 in Bulgaria ,
• in 1918 in most countries of the Tsarist empire Orthodox : Russia , Belarus , Moldova , Ukraine , Georgia , Estonia , Armenia , in Azerbaijan , and in the countries of Central Asia : Turkmenistan , Uzbekistan , Tajikistan , Kyrgyzstan , Kazakhstan ,
• in 1919 the Catholics of Romania ,
• in 1920 for the Orthodox in Romania
• in 1924 in Greece ,
• in 1927 in Turkey ,
• the ^twentieth century in West Africa , Central and South America.

Countries using the Gregorian calendar associated with another calendar are:

• the countries of North Africa : the Algeria , on Morocco , the Tunisian , the Mauritania , the Libyan , of Egypt , the Sudan ,
• the Middle East: Palestine , Israel , the Jordan , the Syrian , the Iraq , the Kuwait , Oman , the Yemen , the Qatar ,
• the major countries of Asia: Vietnam , the People's Republic of China , the Republic of China (Taiwan) , the India and the Burmese , the Thai , the Cambodian , the Mongolia , the Nepal and Japan (calendar by "eras" corresponding to the reign of each emperor).

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

Debates on the Gregorian calendar

If the principle of the Gregorian adjustment was not challenged, it is not true of its internal structure.

In France, critics carried on its links with Christianity , through the Christian era , religious festivals, and references to saints in the calendar. The diaries (or almanacs) were in effect at the time one major media in the French countryside. ^{Non-retroactivity}

The Gregorian calendar is rarely used retroactively. In history , we refer to the Julian calendar for the period before 1582. Thus, in , the dates for the events prior to the formal adoption of the Gregorian calendar are dates of the Julian calendar.

Switching between the two calendars was held on different dates in different countries. Two identical dates in two different countries (between 1582 and France in 1918 in Russia, for example) may correspond to different times. Dating problems sometimes arise when it comes to international events.

Trivia

• Teresa of Avila died on the night of 4 October to 15 October 1582. The date of the feast of Saints being fixed preferably on the day of their death (their "birthday into heaven"), and October 4 is already occupied by the feast of St. Francis of Assisi, the feast of this holy falls naturally October 15. The days of 5 to 14 October 1582 do not exist in countries that have adopted the Gregorian calendar immediately (Vatican, Italy, Spain, Brazil, Portugal). Other dates are not available in other countries or regions according to their date of adoption of the Gregorian calendar.

• Shakespeare and Cervantes died on the same date (April 23, 1616), but not on the same day, the United Kingdom - for its part Anglican - did not immediately adopted the Gregorian calendar.

• The famous astronomer Johannes Kepler amusing to say that Protestants preferred to be at odds with the sun rather than to agree with the Pope, referring to their rejection of the calendar reform.

• In his Essays , Montaigne mentions the difficulties his contemporaries tried to move gradually to the new calendar.

• Vestiges of the Julian calendar still in popular culture. They are removed regularly mark the publication of various calendars, almanacs and other publications agricultural gardening.

Examples: