Exactly 100 years ago, the Russian Republic lived its first day in a new style. Due to the transition from the Julian calendar to the more accurate Gregorian calendar, which was adopted in most European countries back in the 17th century, the first 13 days of February 1918 simply fell out of the calendar, and after January 31, February 14 immediately came. This not only helped synchronize the national calendar with the calendars of other countries, but also led to the fact that the day of the Great October revolution in the Soviet Union, despite the name, they began to celebrate November 7, Pushkin's birthday in June, although he was born, as is known, on May 26, and in mid-January an incomprehensible holiday appeared - the Old New Year. At the same time, the Russian Orthodox Church still uses the Julian calendar, which is why, for example, Orthodox and Catholics celebrate Christmas on different days.

On January 26, 1918, a decree was adopted, according to which the young Soviet Russian Republic switched to the Gregorian calendar generally accepted in Europe. This led not only to a shift in dates, but also to some amendments in determining leap years. In order to understand where the discrepancy between the two calendars comes from, let us first consider the natural processes that were used in their development.

Astronomy and calendar

The most common calendars are based on the relationship between the times of three cyclical astronomical processes: the rotation of the Earth around its axis, the rotation of the Moon around the Earth, and the rotation of the Earth itself around the Sun. These three processes lead to periodic changes that are clearly visible on Earth: the change of day and night, the change of phases of the Moon and the alternation of seasons, respectively. The ratio of the durations of these time intervals underlies the overwhelming number of calendars used by humanity. It is clear that there are other astronomical events noticeable to humans on Earth that occur with convenient regularity (for example, in Ancient Egypt they observed the rise of Sirius, which had the same annual cycle), but using them to develop a calendar is still rather an exception.

Of the three indicated intervals, from an astronomical point of view, the easiest to understand is the shortest of them - the length of the day. Now, for the period of time on the basis of which, in particular, calendars are compiled, they take the average solar day - that is middle period the time it takes the Earth to rotate around its axis relative to the center of the Sun. Solar days are because the center of the Sun is used as a reference point, and it is necessary to average a day over a year due to the fact that due to the ellipticity of the Earth’s orbit and its disturbance by other celestial bodies, the period of revolution of our planet changes over the course of the year, and the longest and longest short days differ from each other by almost 16 seconds.

A method for determining the duration of a solar day, which is calculated by changing the orientation of the Earth relative to the initial position (1) not by a complete rotation of 360 degrees to position (2), but by one revolution relative to the center of the Sun to position (3)

Wikimedia commons

The second time period needed for the calendar is the year. From several possible options To determine the period of one year when compiling a calendar, a seasonal cycle is used, which can be observed when looking at the position of the Sun in the sky from Earth - the so-called tropical year. It is determined by the change in the ecliptic coordinates of the Sun, and one annual cycle corresponds to a change of 360 degrees in its ecliptic longitude (that is, its longitudinal position on the celestial sphere, measured from the vernal equinox point, at which the plane of rotation of the Earth around the Sun and the equatorial plane of the Earth intersect). In this case, the length of the year may vary slightly depending on the choice of the starting point, and, as a rule, the point of the vernal equinox is chosen as the starting position, because for it the error in determining the length of the year is minimal.

The basis of the most common solar calendars today (including the Julian and Gregorian) is the ratio of the time of the daily and annual periods. This ratio, that is, the length of the tropical year in days, is, of course, not an integer and is 365.2422. And how closely the calendar can adjust to this value directly determines its accuracy.

It is worth noting: despite the fact that the duration of one tropical year is almost constant, due to small disturbances in the Earth's orbit it still changes slightly. These disturbances are associated with the influence of the celestial bodies closest to Earth, primarily Mars and Venus, all of them are periodic and have an amplitude of 6 to 9 minutes. The period of each disturbance is two or three years, which together give a 19-year nutation cycle. In addition, the duration of the tropical year does not coincide with the time of the Earth's revolution around the Sun (the so-called sidereal year). This is due to the precession of the earth's axis, which leads to a difference that is now approximately 20 minutes (the length of the sidereal year in days is 365.2564).

The third time period used to compile calendars is the synodic month. It is counted as the time between two identical phases of the Moon (for example, new moons) and is on average equal to 29.5306 solar days. The phases of the moon are determined by the relative position of three celestial bodies - the Earth, the Moon and the Sun and, for example, do not correspond to the periodicity of the position of the Moon on the celestial sphere relative to the stars. In addition, like the tropical year, the synodic month fluctuates greatly in its length.

Lunar calendars based on the changing phases of the Moon were used quite widely, but in most cases they were replaced by solar or solar-lunar calendars. This is explained both by the inconvenience of using lunar calendars due to noticeable variations in the length of the month, and by the natural linking of human activity to seasonal weather changes, which can be associated with the position of the Sun in the sky, but not with the phase of the Moon. Today, lunar calendars are used mainly to determine dates. religious holidays. In particular, the Muslim calendar is lunar, also according to lunar calendar The dates of Old Testament Christian holidays, primarily Easter, are also determined.

Any calendar is based on attempts to connect at least two of these time intervals. But since any of these relations cannot be represented in the form common fraction, then it is impossible to create an absolutely accurate calendar. This problem can be solved relatively in a simple way, without resorting to any calendars at all, but using only one interval, for example the length of the day. This is what they suggest doing, for example, astronomers who simply count the days starting from a certain point in the past (according to the modern calendar, this point corresponds to noon on November 24, 4714 BC). In this case, any time point is determined by the Julian date - a fractional number that corresponds to the number of days that have passed from the beginning of the countdown.

Wikimedia commons

In the figure above: Method for determining ecliptic coordinates celestial body(for example the Sun) on the celestial sphere. They are counted from the point of the vernal equinox.

Julian calendar

But counting time only by days is still not very convenient, and I want to have time intervals of a larger scale at hand. Even understanding that no calendar will allow us to describe with absolute accuracy the relationship between the length of the solar day, the tropical year and the synodic month, we can achieve satisfactory accuracy from it. It is in the degree of accuracy in describing the relationship of two of these three intervals that the difference between the Julian calendar and the Gregorian calendar lies.

Both of these calendars are solar; they are designed to connect the duration of the average solar day and the tropical year. We know that from an astronomical point of view, the length of the tropical year is approximately 365.2422 days. To create a calendar, this number must somehow be described so that there is an integer number of days in each calendar year. The easiest way to do this is to vary the length of the year.

The roughest acceptable rounding gives 365.25 days, and it is on this that the Julian calendar is based. If, with such rounding of the average length of the year, we divide the year into 365 days, then for every four years there will be an error of one day. This is where the structure of the calendar comes from, in which every fourth year is a leap year, that is, it includes one more day than usual. The full cycle of such a calendar is only four years, which makes it very easy to use.

The Julian calendar was developed by Alexandrian astronomers, named after Julius Caesar, and introduced into use in 46 BC. It is interesting that initially an additional day was added in a leap year not by introducing new date- February 29, and due to duplication on February 24.

Certainly, Julian calendar- is far from the first version of the solar calendar. Thus, the basis for all modern solar calendars was the ancient Egyptian solar calendar. It was counted according to the position of ascending Sirius in the sky and included 365 days. And although the Egyptians understood that with such a counting system, for example, the dates of solstices and equinoxes shifted very quickly, for convenience the length of the year did not change. Therefore, every four years there was a shift of one day, and after 1460 years (this interval was called the Great Year of Sothis) the year returned to its original position.

At the same time, in the very Ancient Rome The Julian calendar replaced the previously used Roman calendar, which consisted of ten months and included 354 days. To bring the length of the calendar year into line with the length of the tropical year, an extra month was added to the year every few years.

The Julian calendar turned out to be much more convenient than the Roman calendar, but it was still not very accurate. The difference between 365.2422 and 365.25 is still large, so the inaccuracy of the Julian calendar was noticed quite quickly, primarily due to the shift in the date of the vernal equinox. TO XVI century it has already moved 10 days relative to its initial position, established by the Council of Nicaea in 325 on March 21. Therefore, in order to improve the accuracy of the calendar, it was proposed to make amendments to the existing system of leap years.

Wikimedia commons

Time shift graph summer solstice depending on the year Gregorian calendar. The years are plotted along the abscissa axis, and the calculated actual time of the summer solstice in calendar notation is shown along the ordinate axis (a quarter of a day corresponds to six hours).

Gregorian calendar

The new calendar was introduced into use by Pope Gregory XIII, who issued the bull “Inter gravissimas” in 1582. To more accurately match the tropical calendar year, the number of leap years in the new Gregorian calendar compared to the Julian calendar has decreased by three for every 400 years. Therefore, leap years are no longer those whose serial numbers are completely divisible by 100, but not divisible by 400. That is, 1900 and 2100 are not leap years, but, for example, 2000 was a leap year.

Taking into account the introduced amendments, the duration of one year in days according to the Gregorian calendar was 365.2425, which is much closer to required value at 365.2422 compared to what the Julian calendar suggested. As a result of the proposed amendments, a difference of three days accumulates between the Julian and Gregorian calendars over 400 years. At the same time, the correction was carried out by shifting the day of the vernal equinox in relation to the date established by the Council of Nicaea - March 21, 325, so it amounted to only 10 days (the next day after October 4 in 1582 immediately became October 15), and the zero difference between the calendars corresponds to the first century AD, and the third.

The transition to a more accurate Gregorian calendar in Europe occurred gradually. First, in the 80s of the 16th century, all Catholic countries switched to the Gregorian calendar, and during the 17th and 18th centuries, Protestant states gradually did so. Despite the fact that the reform of Gregory XIII was a measure of the Counter-Reformation, symbolically subordinating calendar time to the bull of the Roman pontiff, its objective advantages were too obvious to be resisted for a long time on religious grounds.

In Russia, the process of transition to an updated calendar was somewhat delayed: until 1700, when most European countries already lived according to the Gregorian calendar, the Byzantine chronology was still adopted in the Russian kingdom. In terms of determining leap years, the Byzantine calendar, developed in the 7th century, corresponded to the Julian calendar, but differed in the names of the months, the start date of the year (September 1) and the starting point for chronology. If the Julian and Gregorian calendars consider the starting point to be January 1 of the year in which Jesus Christ was born, then in the Byzantine version, time is considered “from the creation of the world,” supposedly falling in 5509 BC. (Note that in determining the exact year of Christ's birth, an error of several years was probably made, which is why, according to the Julian calendar, it should not be the first year of our era, but 7–5 BC).

Peter I switched Russia to the Julian calendar in 1700. On the one hand, he saw the need to “synchronize” historical time Russia and Europe, on the other hand, had a deep distrust of the “papist” calendar, not wanting to introduce the “heretical” Easter. True, the Old Believers never accepted his reforms and still count dates according to the Byzantine calendar. The New Believer Orthodox Church switched to the Julian calendar, but at the same time, until the beginning of the 20th century, it resisted the introduction of the more accurate Gregorian calendar.

Due to the practical inconveniences encountered in the conduct of international affairs resulting from the discrepancy between the calendars adopted in Europe and Russian Empire, the question of switching to the Gregorian calendar was raised, especially during the 19th century, more than once. For the first time, such an issue was discussed during the liberal reforms of Alexander I, but it never reached the official level. The problem of the calendar was raised more seriously in 1830; for this purpose, a special committee was even assembled at the Academy of Sciences, but as a result, Nicholas I chose to abandon the reform, agreeing with the arguments of the Minister of Public Education Karl Lieven about the unpreparedness of the people to switch to another calendar system due to insufficient education and possible disturbances.

“Decree on the introduction of the Western European calendar in the Russian Republic”

The next time a serious commission on the need to switch to the Gregorian calendar in the Russian Empire was assembled in the very late XIX century. The commission was formed under the Russian Astronomical Society, but despite the participation of notable scientists in it, in particular Dmitry Mendeleev, it was still decided to abandon the transition due to the insufficient accuracy of the Gregorian calendar.

At the same time, the commission considered the issue of switching to both the Gregorian calendar and an even more accurate version developed by astronomer Johann Heinrich von Medler, professor at the University of Dorpat, in 1884. Mädler proposed using a calendar with a 128-year cycle containing 31 leap years. The average length of a year in days according to such a calendar will be 365.2421875 and an error of one day accumulates over 100 thousand years. However, this project was not accepted either. According to historians, the opinion played a significant role in the refusal of reforms Orthodox Church.

Only in 1917, after the October Revolution and the separation of church and state, the Bolsheviks decided to switch to the Gregorian calendar. By that time, the difference between the two calendars had already reached 13 days. Several options were proposed for the transition to the new style. The first of these involved a gradual transition over 13 years, with a one-day adjustment each year. However, in the end, a second, more radical option was chosen, according to which in 1918 the first half of February was simply canceled, so that after January 31, February 14 came immediately.

Wikimedia commons

Graph of the shift in the time of the vernal equinox according to the New Julian calendar. The abscissa axis shows years, the ordinate axis shows the calculated actual time of the vernal equinox in calendar notation (a quarter of a day corresponds to six hours). The blue vertical line marks the year 1923, when the calendar was developed. The period of time before this date is calculated according to the proleptic New Julian calendar, which extends the dating to an earlier time.

The Julian calendar and the Orthodox Church

The Russian Orthodox Church still continues to use the Julian calendar. The main reason she refuses to switch to the Gregorian calendar is the series binding church holidays(primarily Easter) to the lunar calendar. To calculate the date of Easter, a system of Easter eggs is used, which are based on a comparison lunar months and tropical years (19 tropical years are fairly accurately equal to 235 lunar months).

The transition to the Gregorian calendar, according to representatives of the Russian Orthodox Church, will lead to serious canonical violations. In particular, in some cases when using the Gregorian calendar, the date Catholic Easter turns out to be earlier than the Jewish date or coincides with it, which contradicts the Apostolic canons. After the transition to the Gregorian calendar, Catholics celebrated Easter four times before the Jews (all in the 19th century) and five times simultaneously with them (in the 19th and 20th centuries). Besides, Orthodox priests They also find other reasons not to switch to the Gregorian calendar, such as shortening the duration of some fasts.

At the same time, part of the Orthodox churches at the beginning of the 20th century switched to the New Julian calendar - with amendments introduced by the Serbian astronomer Milutin Milankovic (known primarily for his description of climate cycles). Milanković proposed, instead of subtracting three leap years every 400 years, subtracting seven leap years every 900 years. Thus, the full cycle of the New Julian calendar is 900 years, which makes it even more accurate, but also more difficult to use, even in relation to the Gregorian.

Milankovitch's amendments lead to the fact that the date according to the New Julian calendar may differ from the Gregorian calendar both up and down (in the foreseeable future - by no more than one day). IN this moment the dates of the New Julian and Gregorian calendars coincide, and the next discrepancy between them will appear only in 2800.

The accuracy of the New Julian calendar leads to the accumulation of an error of one day over 43,500 years. This is significantly better than the Gregorian calendar (one day in 3280 years) and, of course, the Julian calendar (one day in 128 years). But, for example, the already mentioned Medler amendments, which were also considered by the Russian Orthodox Church as an alternative to the Julian calendar, make it possible to achieve twice the accuracy (one day per 100 thousand years), even despite a significantly shorter cycle of 128 years.

Returning to the question of dating the October Revolution and Pushkin’s birthday, it is worth noting that they are dated according to the new style (that is, according to the Gregorian calendar), indicating the date in brackets according to the old (Julian) style. They do the same in European countries for dating even those events that occurred before the introduction of the Gregorian calendar, using the so-called proleptic Gregorian calendar, that is, expanding the Gregorian calendar for the period until 1582.

The difference between the dates of Catholic and Orthodox Christmas now fully corresponds to the difference between the Julian and Gregorian calendars. Accordingly, after 2100 Orthodox Christmas will move from January 7 to January 8, and the date difference will increase by one more day.

Alexander Dubov

Since 46 BC, most countries in the world have used the Julian calendar. However, in 1582, by the decision of Pope Gregory XIII, it was replaced by Gregorian. That year, the next day after the fourth of October was not the fifth, but the fifteenth of October. Now the Gregorian calendar is officially adopted in all countries except Thailand and Ethiopia.

Reasons for adopting the Gregorian calendar

The main reason for the introduction of a new chronology system was the movement of the vernal equinox, depending on which the date of the celebration of Christian Easter was determined. Due to discrepancies between the Julian and tropical calendars (the tropical year is the length of time during which the sun completes one cycle of changing seasons), the day of the vernal equinox gradually shifted to more and more early dates. At the time of the introduction of the Julian calendar, it fell on March 21, both according to the accepted calendar system and in fact. But by the 16th century, the difference between the tropical and Julian calendars was already about ten days. As a result, the vernal equinox no longer fell on March 21, but on March 11.

Scientists paid attention to the above problem long before the adoption of the Gregorian chronology system. Back in the 14th century, Nikephoros Grigora, a scientist from Byzantium, reported this to Emperor Andronicus II. According to Grigora, it was necessary to revise the calendar system that existed at that time, since otherwise the date of Easter would continue to shift to a later and later time. However, the emperor did not take any action to eliminate this problem, fearing protest from the church.

Subsequently, other scientists from Byzantium also spoke about the need to switch to a new calendar system. But the calendar continued to remain unchanged. And not only because of the rulers’ fear of causing indignation among the clergy, but also because the further the Christian Easter, the less chance it had of coinciding with the Jewish Passover. This was unacceptable according to church canons.

By the 16th century, the problem had become so urgent that the need to solve it was no longer in doubt. As a result, Pope Gregory XIII assembled a commission, which was tasked with carrying out all the necessary research and creating a new calendar system. The results obtained were displayed in the bullet “Among the most important”. It was she who became the document with which the adoption of the new calendar system began.

The main disadvantage of the Julian calendar is its lack of accuracy in relation to the tropical calendar. In the Julian calendar, all years that are divisible by 100 without a remainder are considered leap years. As a result, the difference with the tropical calendar increases every year. Approximately every century and a half it increases by 1 day.

The Gregorian calendar is much more accurate. It has less leap years. In this chronology system, leap years are considered to be years that:

1. divisible by 400 without remainder;
2. divisible by 4 without a remainder, but not divisible by 100 without a remainder.

Thus, 1100 or 1700 years in the Julian calendar are considered leap years, since they are divisible by 4 without a remainder. In the Gregorian calendar, from those that have already passed since its adoption, 1600 and 2000 are considered leap years.

Immediately after the introduction of the new system, it was possible to eliminate the difference between the tropical and calendar years, which at that time was already 10 days. Otherwise, due to errors in calculations, an extra year would accumulate every 128 years. In the Gregorian calendar, an extra day occurs only every 10,000 years.

Not all modern states adopted the new chronology system immediately. The Catholic states were the first to switch to it. In these countries, the Gregorian calendar was officially adopted either in 1582 or shortly after the decree of Pope Gregory XIII.

In a number of states, the transition to a new calendar system was associated with popular unrest. The most serious of them took place in Riga. They lasted for five whole years - from 1584 to 1589.

There were also some funny situations. So, for example, in Holland and Belgium, due to the official adoption of the new calendar, after December 21, 1582, January 1, 1583 came. As a result, the inhabitants of these countries were left without Christmas in 1582.

Russia was one of the last to adopt the Gregorian calendar. The new system was officially introduced on the territory of the RSFSR on January 26, 1918 by decree of the Council of People's Commissars. In accordance with this document, immediately after January 31 of that year, February 14 came on the territory of the state.

Later than in Russia, the Gregorian calendar was introduced only in a few countries, including Greece, Turkey and China.

After the official adoption of the new chronology system, Pope Gregory XIII sent a proposal to Constantinople to switch to a new calendar. However, she was met with refusal. Its main reason was the inconsistency of the calendar with the canons of celebrating Easter. However, later most Orthodox churches switched to the Gregorian calendar.

Today, only four Orthodox churches use the Julian calendar: Russian, Serbian, Georgian and Jerusalem.

Rules for specifying dates

In accordance with the generally accepted rule, dates falling between 1582 and the moment the Gregorian calendar was adopted in the country are indicated in both the old and new styles. In this case, the new style is indicated in quotation marks. Earlier dates are indicated according to the proleptic calendar (i.e., a calendar used to indicate dates earlier than the date the calendar appeared). In countries where the Julian calendar was adopted, dates before 46 BC. e. are indicated according to the proleptic Julian calendar, and where there was none - according to the proleptic Gregorian calendar.

As in other Christian countries, from the end of the 10th century in Rus', the Julian calendar was used, based on observations of the visible movement of the Sun across the sky. It was introduced in Ancient Rome by Gaius Julius Caesar in 46 BC. e.

The calendar was developed by the Alexandrian astronomer Sosigenes based on the calendar Ancient Egypt. When Rus' adopted Christianity in the 10th century, the Julian calendar came with it. However average duration The year in the Julian calendar is 365 days and 6 hours (i.e. there are 365 days in a year, and an additional day is added every fourth year). While the duration of the astronomical solar year is 365 days 5 hours 48 minutes and 46 seconds. That is, the Julian year was 11 minutes 14 seconds longer than the astronomical year and, therefore, lagged behind the real change of years.

By 1582, the difference between the Julian calendar and the real change of years was already 10 days.

This led to a reform of the calendar, which was carried out in 1582 by a special commission created by Pope Gregory XIII. The difference was eliminated when, after October 4, 1582, it was ordered to count not October 5, but immediately October 15. After the name of the pope, the new, reformed calendar began to be called the Gregorian calendar.

In this calendar, unlike the Julian calendar, the final year of the century, if it is not divisible by 400, is not a leap year. Thus, the Gregorian calendar has 3 fewer leap years in each four-hundredth anniversary than the Julian calendar. The Gregorian calendar retained the names of the months of the Julian calendar, the additional day in the leap year is February 29, and the beginning of the year is January 1.

The transition of countries around the world to the Gregorian calendar was long. First, the reform took place in Catholic countries (Spain, Italian states, the Polish-Lithuanian Commonwealth, a little later in France, etc.), then in Protestant countries (in Prussia in 1610, in all German states by 1700, in Denmark in 1700, in Great Britain in 1752, in Sweden in 1753). And only in the 19th-20th centuries the Gregorian calendar was adopted in some Asian (in Japan in 1873, China in 1911, Turkey in 1925) and Orthodox (in Bulgaria in 1916, in Serbia in 1919, in Greece in 1924 year) states.

In the RSFSR, the transition to the Gregorian calendar was carried out according to the decree of the Council of People's Commissars of the RSFSR “On the introduction of the Western European calendar in the Russian Republic” dated February 6, 1918 (January 26, old style).

The calendar problem in Russia has been discussed several times. In 1899, a Commission on the issue of calendar reform in Russia worked under the Astronomical Society, which included Dmitry Mendeleev and historian Vasily Bolotov. The commission proposed modernizing the Julian calendar.

“Taking into account: 1) that in 1830 the petition of the Imperial Academy of Sciences for the introduction of the Gregorian calendar in Russia was rejected by Emperor Nicholas I and 2) that the Orthodox states and the entire Orthodox population of the East and West rejected the attempts of representatives of Catholicism to introduce the Gregorian calendar in Russia, the Commission unanimously decided to reject all proposals for the introduction of the Gregorian calendar in Russia and, without being embarrassed by the choice of reform, to settle on one that would combine the idea of ​​​​truth and possible accuracy, both scientific and historical, in relation to Christian chronology in Russia,” reads Resolution of the Commission on the reform of the calendar in Russia from 1900.

Such a long use of the Julian calendar in Russia was due to the position of the Orthodox Church, which had a negative attitude towards the Gregorian calendar.

After the church was separated from the state in the RSFSR, linking the civil calendar to the church calendar lost its relevance.

The difference in calendars created inconvenience in relations with Europe, which was the reason for the adoption of the decree “in order to establish in Russia the same calculation of time with almost all cultural nations.”

The question of reform was raised in the fall of 1917. One of the projects under consideration proposed a gradual transition from the Julian calendar to the Gregorian calendar, dropping a day each year. But, since the difference between the calendars by that time was 13 days, the transition would take 13 years. Therefore, Lenin supported the option of an immediate transition to a new style. The church refused to switch to the new style.

“The first day after January 31 of this year should be considered not February 1, but February 14, the second day should be considered the 15th, etc.,” read the first paragraph of the decree. The remaining points indicated how new deadlines for fulfilling any obligations should be calculated and on what dates citizens would be able to receive their salaries.

The change of dates has created confusion with the celebration of Christmas. Before the transition to the Gregorian calendar in Russia, Christmas was celebrated on December 25, but now it has moved to January 7. As a result of these changes, in 1918 there was no Christmas at all in Russia. The last Christmas was celebrated in 1917, which fell on December 25th. And next time Orthodox holiday was celebrated already on January 7, 1919.

The converter converts dates to the Gregorian and Julian calendars and calculates the Julian date; for the Julian calendar, the Latin and Roman versions are displayed.

Notes

• Gregorian calendar(“new style”) introduced in 1582 AD. e. Pope Gregory XIII, so that the day of the vernal equinox corresponds on a certain day(21 March). Earlier dates are converted using standard rules for Gregorian leap years. Conversion up to 2400g is possible.
• Julian calendar(“old style”) introduced in 46 BC. e. Julius Caesar and totaled 365 days; Every third year was a leap year. This error was corrected by Emperor Augustus: from 8 BC. e. and until 8 AD e. Additional days of leap years were skipped. Earlier dates are converted using standard rules for Julian leap years.
• Roman version The Julian calendar was introduced around 750 BC. e. Due to the fact that the number of days in the Roman calendar year changed, dates before 8 AD. e. are not accurate and are presented for demonstration purposes. The chronology was carried out from the founding of Rome ( ab Urbe condita) - 753/754 BC e. Dates before 753 BC e. not calculated.
• Month names Roman calendar are agreed modifiers (adjectives) with a noun mensis'month':

• Days of the month determined by the phases of the moon. In different months, the Kalends, Nonas and Ides fell on different dates:

The first days of the month are determined by counting the days from the upcoming Nons, after the Nons - from the Ides, after the Ides - from the upcoming Kalends. The preposition is used ante‘to’ with accusative case (accusatīvus):

a. d. XI Kal. Sept. (short form);

ante diem undecĭmum Kalendas Septembres (full form).

The ordinal number agrees with the form diem, that is, put in the accusative case singular masculine (accusatīvus singulāris masculīnum). Thus, the numerals take the following forms:

If the day falls on the Kalends, Nones or Ides, then the name of this day (Kalendae, Nonae, Idūs) and the name of the month are put in the instrumental case plural female(ablatīvus plurālis feminīnum), for example:

The day immediately preceding the Kalends, Nones or Idams is designated by the word pridie(‘the day before’) with the feminine accusative plural (accusatīvus plurālis feminīnum):

Thus, month adjectives can take the following forms:

• Julian date is the number of days that have passed since noon on January 1, 4713 BC. e. This date is arbitrary and was chosen only for coordination various systems chronology.

In Europe, starting in 1582, the reformed (Gregorian) calendar gradually spread. The Gregorian calendar provides a much more accurate approximation of the tropical year. The Gregorian calendar was first introduced by Pope Gregory XIII in Catholic countries on October 4, 1582, replacing the previous one: the next day after Thursday, October 4, became Friday, October 15.
The Gregorian calendar (“new style”) is a time calculation system based on the cyclic revolution of the Earth around the Sun. The length of the year is taken to be 365.2425 days. The Gregorian calendar contains 97 by 400 years.

Difference between Julian and Gregorian calendars

At the time of the introduction of the Gregorian calendar, the difference between it and the Julian calendar was 10 days. However, this difference between the Julian and Gregorian calendars gradually increases over time due to differences in the rules for determining leap years. Therefore, when determining which date of the “new calendar” a particular date of the “old calendar” falls on, it is necessary to take into account the century in which the event took place. For example, if in the 14th century this difference was 8 days, then in the 20th century it was already 13 days.

This follows the distribution of leap years:

• a year whose number is a multiple of 400 is a leap year;
• other years, the number of which is a multiple of 100, are non-leap years;
• other years, the number of which is a multiple of 4, are leap years.

Thus, 1600 and 2000 were leap years, but 1700, 1800 and 1900 were not leap years. Also, 2100 will not be a leap year. An error of one day compared to the year of the equinoxes in the Gregorian calendar will accumulate in approximately 10 thousand years (in the Julian calendar - approximately in 128 years).

Time of approval of the Gregorian calendar

The Gregorian calendar, adopted in most countries of the world, was not put into use immediately:
1582 - Italy, Spain, Portugal, Poland, France, Lorraine, Holland, Luxembourg;
1583 - Austria (part), Bavaria, Tyrol.
1584 - Austria (part), Switzerland, Silesia, Westphalia.
1587 - Hungary.
1610 - Prussia.
1700 - Protestant German states, Denmark.
1752 - Great Britain.
1753 - Sweden, Finland.
1873 - Japan.
1911 - China.
1916 - Bulgaria.
1918 - Soviet Russia.
1919 - Serbia, Rumania.
1927 - Türkiye.
1928 - Egypt.
1929 - Greece.

Gregorian calendar in Russia

As you know, until February 1918, Russia, like most Orthodox countries, lived according to the Julian calendar. The “new style” of chronology appeared in Russia in January 1918, when the Council of People's Commissars replaced the traditional Julian calendar with the Gregorian calendar. As stated in the Decree of the Council of People's Commissars, this decision was made “in order to establish in Russia the same calculation of time with almost all cultural peoples.” In accordance with the decree, the dates of all obligations were considered to have occurred 13 days later. Until July 1, 1918, a kind of transition period was established when it was allowed to use the old style calendar. But at the same time, the document clearly established the order of writing old and new dates: it was necessary to write “after the date of each day according to the new calendar, in brackets the number according to the calendar that was still in force.”

Events and documents are dated with a double date in cases where it is necessary to indicate the old and new styles. For example, for anniversaries, major events in all works of a biographical nature and dates of events and documents on history international relations, associated with countries where the Gregorian calendar was introduced earlier than in Russia.

New style date (Gregorian calendar)