is a number system for large periods of time, based on the periodicity of the Earth’s movement around the Sun.
The length of a year in the Gregorian calendar is 365.2425 days; there are 97 leap years per 400 years.
The Gregorian calendar is an improvement of the Julian calendar. It was introduced in 1582 by Pope Gregory XIII, replacing the imperfect Julian.
The Gregorian calendar is usually called the new style, and the Julian calendar is called the old style. The difference between the old and new styles is 11 days for the 18th century, 12 days for the 19th century, 13 days for the 20th and 21st centuries, 14 days for the 22nd century.
Adoption of the Gregorian calendar in different countries
Gregorian calendar different countries was introduced into different times. First on a new style passed to Italy in 1582. The Italians were followed by Spain, Portugal, Poland, France, Holland and Luxembourg. In the 1580s, these countries were joined by Austria, Switzerland and Hungary.
Great Britain, Germany, Denmark, Norway, Finland and Sweden introduced the new style in the 18th century. The Japanese introduced the Gregorian calendar in the 19th century. At the beginning of the 20th century, the new style was joined in China, Bulgaria, Serbia, Romania, Greece, Turkey and Egypt.
In Rus', where people lived according to the Julian calendar since the 10th century, the new European chronology was introduced by decree of Peter I in 1700. At the same time, the Julian calendar was preserved in Russia, according to which Russian culture still lives. Orthodox Church. The Gregorian calendar was introduced after the October Revolution of 1917 - from February 14, 1918.
Disadvantages of the Gregorian calendar
The Gregorian calendar is not absolute and has inaccuracies, although it is consistent with natural phenomena. The length of its year is 26 seconds longer than the tropical year and accumulates an error of 0.0003 days per year, which is three days per 10 thousand years.
In addition, the Gregorian calendar does not take into account the slowing of the Earth's rotation, which lengthens the day by 0.6 seconds per 100 years.
Also, the Gregorian calendar does not meet the needs of society. Chief among its shortcomings is the variability of the number of days and weeks in months, quarters and half-years.
Problems with the Gregorian calendar
There are four main problems with the Gregorian calendar:
- Inconsistency of the Gregorian calendar with the tropical year. True, such a correspondence is generally unattainable due to the fact that the tropical year does not contain an integer number of days. Because of the need to add extra days to the year from time to time, there are two types of years - ordinary and leap years. Since the year can begin on any day of the week, this gives seven types of ordinary years and seven types of leap years - a total of 14 types of years. To fully reproduce them you need to wait 28 years.
- The length of the months varies: they can contain from 28 to 31 days, and this unevenness leads to certain difficulties in economic calculations and statistics.|
- Neither ordinary nor leap years contain an integer number of weeks. Semi-years, quarters and months also do not contain a whole and equal number of weeks.
- From week to week, from month to month and from year to year, the correspondence of dates and days of the week changes, so it is difficult to establish the moments of various events.
New calendar projects
In 1954 and 1956, drafts of a new calendar were discussed at sessions of the UN Economic and Social Council (ECOSOC), but the final resolution of the issue was postponed.
In Russia State Duma A bill was introduced proposing to return the country to the Julian calendar from January 1, 2008. Deputies Viktor Alksnis, Sergei Baburin, Irina Savelyeva and Alexander Fomenko proposed establishing a transition period from December 31, 2007, when, for 13 days, chronology will be carried out simultaneously according to the Julian and Gregorian calendars. In April 2008, the bill was rejected by a majority vote.
07.12.2015
Gregorian calendar - modern system calculus based on astronomical phenomena, namely, on the cyclic revolution of our planet around the Sun. The length of the year in this system is 365 days, with every fourth year becoming a leap year and equal to 364 days.
History of origin
The date of approval of the Gregorian calendar is October 4, 1582. This calendar replaced the Julian calendar in force until that time. Most modern countries live according to the new calendar: look at any calendar and you will get a clear idea of the Gregorian system. According to the Gregorian Calculus, the year is divided into 12 months, the duration of which is 28, 29, 30 and 31 days. The calendar was introduced by Pope Gregory XIII.
The transition to a new calculation entailed the following changes:
- At the time of adoption, the Gregorian calendar immediately shifted the current date by 10 days and corrected the errors accumulated by the previous system;
- In the new calculus, a more correct rule for determining a leap year began to apply;
- The rules for calculating the day of Christian Easter have been modified.
In the year the new system was adopted, Spain, Italy, France, and Portugal joined the chronology, and a couple of years later other European countries joined them. In Russia, the transition to the Gregorian calendar took place only in the 20th century - in 1918. In the territory that was by that time under the control of Soviet power, it was announced that after January 31, 1918, February 14 would immediately follow. For a long time citizens new country could not get used to the new system: the introduction of the Gregorian calendar in Russia caused confusion in documents and minds. In official papers, dates of birth and other significant events for a long time indicated according to the style and new style.
By the way, the Orthodox Church still lives according to the Julian calendar (unlike the Catholic one), so the days church holidays(Easter, Christmas) in Catholic countries do not coincide with Russian ones. According to the highest clergy of the Orthodox Church, the transition to the Gregorian system will lead to canonical violations: the rules of the Apostles do not allow the celebration of Holy Easter to begin on the same day as the Jewish pagan holiday.
China was the last to switch to the new timekeeping system. This happened in 1949 after the proclamation of the People's Republic of China. In the same year, the world-accepted calculation of years was established in China - from the Nativity of Christ.
At the time of approval of the Gregorian calendar, the difference between the two calculation systems was 10 days. By now, due to different quantities For leap years, the discrepancy increased to 13 days. By March 1, 2100, the difference will already reach 14 days.
Compared to the Julian calendar, the Gregorian calendar is more accurate from an astronomical point of view: it is as close as possible to the tropical year. The reason for the change in systems was the gradual shift of the equinox to Julian calendar: this caused a discrepancy between the Easter full moons and the astronomical ones.
All modern calendars have a familiar appearance to us precisely thanks to the transition of leadership Catholic Church to a new time calculation. If the Julian calendar continued to function, the discrepancies between the actual (astronomical) equinoxes and Easter holidays would increase even more, which would introduce confusion into the very principle of determining church holidays.
By the way, the Gregorian calendar itself is not 100% accurate from an astronomical point of view, but the error in it, according to astronomers, will accumulate only after 10,000 years of use.
People continue to use it successfully new system time is already more than 400 years. A calendar is still a useful and functional thing that everyone needs to coordinate dates, plan business and personal life.
Modern printing production has achieved unprecedented technological development. Any commercial or public organization can order calendars with their own symbols from the printing house: they will be produced promptly, with high quality, and at an adequate price.
Gregorian calendar
This calculator allows you to convert the date from the Julian to the Gregorian calendar, as well as calculate the date of Orthodox Easter according to the old style
* to calculate Easter according to the new style, you must enter the date obtained according to the old style into the calculation form
(amendment + 13 days to the Julian calendar)
2019 non-leap
IN 2019 Orthodox Easter falls on April 15(according to the Julian calendar)
The date of Orthodox Easter is calculated using the algorithm of Carl Friedrich Gauss
Disadvantages of the Julian calendar
In 325 AD e. The Nicene Church Council took place. It adopted the Julian calendar for the entire Christian world, according to which at that time the spring equinox fell on March 21. For the church it was important point in determining the time of celebration of Easter - one of the most important religious holidays. By accepting the Julian calendar, the clergy believed that it was perfectly accurate. However, as we know, for every 128 years an error of one day accumulates.
An error in the Julian calendar led to the fact that the actual time of the vernal equinox no longer coincides with the calendar. The moment of equality between day and night moved to earlier and earlier dates: first to March 20, then to 19, 18, etc. By the second half of the 16th century. the error was 10 days: according to the Julian calendar, the moment of the equinox was supposed to occur on March 21, but in reality it already occurred on March 11.
History of the Gregorian reform.
The inaccuracy of the Julian calendar was discovered in the first quarter of the 14th century. Thus, in 1324, the Byzantine scientist Nikephoros Grigora drew the attention of Emperor Andronikos II to the fact that the spring equinox no longer falls on March 21 and, therefore, Easter will gradually be pushed back to a later time. Therefore, he considered it necessary to correct the calendar and with it the calculation of Easter. However, the emperor rejected Grigor's proposal, considering the reform practically impracticable due to the impossibility of reaching an agreement on this matter between individual Orthodox churches.
The inaccuracy of the Julian calendar was also pointed out by the Greek scientist Matvey Vlastar, who lived in Byzantium in the first half of the 14th century. However, he did not consider it necessary to make corrections, since he saw in this some “advantage”, consisting in the fact that the delay of the Orthodox Easter saves it from coinciding with the Jewish Passover. Their simultaneous celebration was prohibited by the decrees of some “Ecumenical” councils and various church canons.
It is interesting to note that in 1373, the Byzantine scientist Isaac Argir, who more deeply understood the need to correct the Julian calendar and the rules for calculating Easter, considered such an event useless. The reason for this attitude towards the calendar was explained by the fact that Argir was deeply confident in the coming “doomsday” and the end of the world in 119 years, since it would be 7000 years “since the creation of the world.” Is it worth it to reform the calendar if there is so little time left for the life of all humanity!
The need to reform the Julian calendar was also understood by many representatives of the Catholic Church. In the XIV century. Pope Clement VI spoke in favor of correcting the calendar.
In March 1414, the calendar issue was discussed at the initiative of Cardinal Pierre d'Ailly. The shortcomings of the Julian calendar and the inaccuracy of the existing Paschals were the subject of discussion at the Council of Basel in March 1437. Here, the outstanding philosopher and scientist of the Renaissance, Nicholas of Cusa (1401-1464), one of the predecessors of Copernicus, came up with his project.
In 1475, Pope Sixtus IV began preparations for the reform of the calendar and the correction of Easter. For this purpose, he invited the outstanding German astronomer and mathematician Regiomontanus (1436-1476) to Rome. However, the unexpected death of the scientist forced the pope to postpone the implementation of his intention.
In the 16th century Two more “ecumenical” councils dealt with issues of calendar reform: the Lateran (1512-1517) and the Trent Council (1545-1563). When in 1514 the Lateran Council created a commission to reform the calendar, the Roman Curia invited the then well-known Polish astronomer Nicolaus Copernicus (1473-1543) in Europe to come to Rome and take part in the work of the calendar commission. However, Copernicus avoided participating in the commission and pointed out the prematureness of such a reform, since, in his opinion, by this time the length of the tropical year had not been established accurately enough.
Gregorian reform. By the middle of the 16th century. the question of calendar reform became so widespread and the importance of its solution turned out to be so necessary that postponing this issue further was considered undesirable. That is why in 1582, Pope Gregory XIII created a special commission, which included Ignatius Danti (1536-1586), a famous professor of astronomy and mathematics at the University of Bologna at that time. This commission was tasked with developing a draft of a new calendar system.
After reviewing all the proposed options for the new calendar, the commission approved the project, the author of which was the Italian mathematician and physician Luigi Lilio (or Aloysius Lilius, 1520-1576), a teacher of medicine at the University of Perugia. This project was published in 1576 by the scientist’s brother, Antonio Lilio, who, during Luigi’s lifetime, took an active part in the development of the new calendar.
Lilio's project was accepted by Pope Gregory XIII. On February 24, 1582, he issued a special bull (Fig. 11), according to which the count of days was moved forward 10 days and the day after Thursday October 4, 1582, Friday was ordered to be counted not as October 5, but as October 15. This immediately corrected the error that had accumulated since the Council of Nicaea, and the spring equinox again fell on March 21.
It was more difficult to resolve the issue of introducing an amendment to the calendar that would ensure for long periods of time that the calendar date of the vernal equinox coincided with its actual date. To do this, it was necessary to know the length of the tropical year.
By this time, astronomical tables, known as the “Prussian Tables,” had already been published. They were compiled by the German astronomer and mathematician Erasmus Reinhold (1511-1553) and published in 1551. The length of the year in them was taken to be 365 days 5 hours 49 minutes 16 seconds, i.e. more than the true value of the tropical year by only 30 seconds. The length of the year of the Julian calendar differed from it by 10 minutes. 44 sec. per year, which gave an error per day for 135 years, and for 400 years - slightly more than three days.
Consequently, the Julian calendar moves ahead by three days every 400 years. Therefore, in order to avoid new errors, it was decided to exclude 3 days from the count every 400 years. According to the Julian calendar, there should be 100 leap years in 400 years. To implement the reform, it was necessary to reduce their number to 97. Lilio proposed to consider as simple those century years of the Julian calendar, the number of hundreds in which is not divisible by 4. Thus, in the new calendar, only those century years are considered leap years, the number of centuries of which is divisible by 4 without remainder. Such years are: 1600, 2000, 2400, 2800, etc. The years 1700, 1800, 1900, 2100, etc. will be simple.
The reformed calendar system was called the Gregorian or "new style".
Is the Gregorian calendar accurate? We already know that the Gregorian calendar is also not entirely accurate. After all, when correcting the calendar, they began to throw out three days every 400 years, while such an error accumulates only in 384 years. To determine the error of the Gregorian calendar, we calculate the average length of the year in it.
In a period of 400 years there will be 303 years of 365 days and 97 years of 366 days. The total number of days in a four-century period will be 303 × 365 + 97 × 366 == 110,595 + 35,502 = 146,097. Divide this number by 400. Then we get 146097/400 = 365.242500 accurate to the sixth decimal place. This is the average length of a year in the Gregorian calendar. This value differs from the currently accepted value of the length of the tropical year by only 0.000305 average day, which gives a difference of a whole day over 3280 years.
The Gregorian calendar could be improved and made even more accurate. To do this, it is enough to consider one leap year every 4000 years as simple. Such years could be 4000, 8000, etc. Since the error of the Gregorian calendar is 0.000305 days per year, then in 4000 years it will be 1.22 days. If you correct the calendar for one more day in 4000 years, then an error of 0.22 days will remain. Such an error will increase to a full day in only 18,200 years! But such accuracy is no longer of any practical interest.
When and where was the Gregorian calendar first introduced? The Gregorian calendar did not immediately become widespread. In countries where Catholicism was the dominant religion (France, Italy, Spain, Portugal, Poland, etc.), it was introduced in 1582 or somewhat later. Other countries recognized it only after tens and hundreds of years.
In states where Lutheranism was strongly developed, for a long time they were guided by the saying that “it is better to separate from the Sun than to get along with the Pope.” The Orthodox Church opposed the new style even longer.
In a number of countries, great difficulties had to be overcome when introducing the Gregorian calendar. History knows of the “calendar riots” that arose in 1584 in Riga and were directed against the decree of the Polish king Stefan Batory on the introduction of a new calendar not only in Poland, but also in the Duchy of Zadvina, which was at that time under Lithuanian-Polish domination. The struggle of the Latvian people against Polish dominance and Catholicism continued for several years. The “calendar riots” stopped only after the leaders of the uprising, Giese and Brinken, were arrested and subjected to brutal torture and executed.
In England, the introduction of a new calendar was accompanied by a postponement of the start of the new year from March 25 to January 1. Thus, the year 1751 in England consisted of only 282 days. Lord Chesterfield, on whose initiative calendar reform was carried out in England, was pursued by the townspeople shouting: “Give us our three months.”
In the 19th century Attempts were made to introduce the Gregorian calendar in Russia, but each time these attempts failed due to opposition from the church and government. Only in 1918, immediately after the establishment of Soviet power in Russia, was calendar reform implemented.
The difference between the two calendar systems. By the time of the calendar reform, the difference between the old and new styles was 10 days. This amendment remained the same in the 17th century, since 1600 was a leap year both according to the new style and the old one. But in the 18th century. the amendment increased to 11 days in the 19th century. - up to 12 days and, finally, in the 20th century. - up to 13 days.
How to set the date after which the amendment changes its value?
The reason for the change in the magnitude of the correction depends on the fact that in the Julian calendar the years 1700, 1800 and 1900 are leap years, i.e. these years contain 29 days in February, but in the Gregorian calendar they are not leap years and have only 28 days in February.
To convert the Julian date of any event that occurred after the reform of 1582 to the new style, you can use the table:
From this table it is clear that the critical days, after which the amendment is increased by one day, are February 29, old style, of those century years in which, according to the rules of the Gregorian reform, one day was removed from the count, i.e., the years 1700, 1800, 1900 , 2100, 2200, etc. Therefore, starting from March 1 of these years, again according to the old style, the amendment increases by one day.
A special place is occupied by the issue of recalculating the dates of events that took place before the introduction of the Gregorian calendar in the 16th century. Such a recount is also important when they are going to celebrate the anniversary of any historical event. Thus, in 1973, humanity celebrated the 500th anniversary of the birth of Copernicus. It is known that he was born on February 19, 1473 according to the old style. But we now live according to the Gregorian calendar and therefore it was necessary to recalculate the date of interest to us to the new style. How was this done?
Since in the 16th century. the difference between the two calendar systems was 10 days, then, knowing the speed with which it changes, it is possible to establish the magnitude of this difference for the various centuries preceding the calendar reform. It should be borne in mind that in 325 the Council of Nicaea adopted the Julian calendar and the spring equinox then fell on March 21. Taking all this into account, we can continue the table. 1 in reverse side and receive the following translation amendments:
| Date interval | Amendment |
| from 1.III.300 to 29.II.400 | 0 days |
| from 1.III.400 to 29.II.500 | + 1 day |
| from 1.III.500 to 29.II.600 | + 2 days |
| from 1.III.600 to 29.II.700 | + 3 days |
| from 1.III.700 to 29.II.900 | + 4 days |
| from 1.III.900 to 29.II.1000 | + 5 days |
| from 1.III.1000 to 29.II.1100 | + 6 days |
| from 1.III.1100 to 29.II.1300 | + 7 days |
| from 1.III.1300 to 29.II.1400 | + 8 days |
| from 1.III.1400 to 29.II.1500 | + 9 days |
| from 1.III.1500 to 29.II.1700 | + 10 days |
From this table it is clear that for the date February 19, 1473, the correction will be +9 days. Consequently, the 500th anniversary of the birth of Copernicus was celebrated on February 19 +9-28, 1973.
- a number system for large periods of time, based on periodicity visible movements celestial bodies
The most common solar calendar is based on the solar (tropical) year - the period of time between two successive passages of the center of the Sun through the vernal equinox.
A tropical year has approximately 365.2422 average solar days.
The solar calendar includes the Julian calendar, the Gregorian calendar and some others.
The modern calendar is called the Gregorian (new style), it was introduced by Pope Gregory XIII in 1582 and replaced the Julian calendar ( old style), which has been in use since the 45th century BC.
The Gregorian calendar is a further refinement of the Julian calendar.
In the Julian calendar, proposed by Julius Caesar, the average length of a year in an interval of four years was 365.25 days, which is 11 minutes 14 seconds longer than the tropical year. Over time, the onset of seasonal phenomena according to the Julian calendar occurred on increasingly earlier dates. Particularly strong discontent was caused by the constant shift in the date of Easter, associated with the spring equinox. In 325, the Council of Nicaea decreed a single date for Easter for the entire Christian church.
© Public Domain
© Public Domain
In subsequent centuries, many proposals were made to improve the calendar. The proposals of the Neapolitan astronomer and physician Aloysius Lilius (Luigi Lilio Giraldi) and the Bavarian Jesuit Christopher Clavius were approved by Pope Gregory XIII. On February 24, 1582, he issued a bull (message) introducing two important additions to the Julian calendar: 10 days were removed from the 1582 calendar - October 4 was immediately followed by October 15. This measure made it possible to preserve March 21 as the date of the vernal equinox. In addition, three out of every four century years were to be considered ordinary years and only those divisible by 400 were to be considered leap years.
1582 was the first year of the Gregorian calendar, called the new style.
The Gregorian calendar was introduced at different times in different countries. The first countries to switch to the new style in 1582 were Italy, Spain, Portugal, Poland, France, Holland and Luxembourg. Then in the 1580s it was introduced in Austria, Switzerland, and Hungary. In the 18th century, the Gregorian calendar began to be used in Germany, Norway, Denmark, Great Britain, Sweden and Finland, and in the 19th century - in Japan. At the beginning of the 20th century, the Gregorian calendar was introduced in China, Bulgaria, Serbia, Romania, Greece, Turkey and Egypt.
In Rus', along with the adoption of Christianity (10th century), the Julian calendar was established. Since the new religion was borrowed from Byzantium, the years were counted according to the Constantinople era “from the creation of the world” (5508 BC). By decree of Peter I in 1700, the European chronology was introduced in Russia - “from the Nativity of Christ”.
December 19, 7208 from the creation of the world, when the reformation decree was issued, in Europe corresponded to December 29, 1699 from the Nativity of Christ according to the Gregorian calendar.
At the same time, the Julian calendar was preserved in Russia. The Gregorian calendar was introduced after the October Revolution of 1917 - from February 14, 1918. The Russian Orthodox Church, preserving traditions, lives according to the Julian calendar.
The difference between the old and new styles is 11 days for the 18th century, 12 days for the 19th century, 13 days for the 20th and 21st centuries, 14 days for the 22nd century.
Although the Gregorian calendar is quite consistent with natural phenomena, it is also not completely accurate. The length of the year in the Gregorian calendar is 26 seconds longer than the tropical year and accumulates an error of 0.0003 days per year, which is three days per 10 thousand years. The Gregorian calendar also does not take into account the slowing rotation of the Earth, which lengthens the day by 0.6 seconds per 100 years.
The modern structure of the Gregorian calendar also does not fully meet the needs public life. Chief among its shortcomings is the variability of the number of days and weeks in months, quarters and half-years.
There are four main problems with the Gregorian calendar:
— Theoretically, the civil (calendar) year should have the same length as the astronomical (tropical) year. However, this is impossible, since the tropical year does not contain an integer number of days. Because of the need to add an extra day to the year from time to time, there are two types of years - ordinary and leap years. Since the year can begin on any day of the week, this gives seven types of ordinary years and seven types of leap years—for a total of 14 types of years. To fully reproduce them you need to wait 28 years.
— The length of the months varies: they can contain from 28 to 31 days, and this unevenness leads to certain difficulties in economic calculations and statistics.|
— Neither ordinary nor leap years contain an integer number of weeks. Semi-years, quarters and months also do not contain a whole and equal number of weeks.
— From week to week, from month to month and from year to year, the correspondence of dates and days of the week changes, so it is difficult to establish the moments of various events.
In 1954 and 1956, drafts of a new calendar were discussed at sessions of the UN Economic and Social Council (ECOSOC), but the final resolution of the issue was postponed.
In Russia, the State Duma was proposing to return the country to the Julian calendar from January 1, 2008. Deputies Viktor Alksnis, Sergei Baburin, Irina Savelyeva and Alexander Fomenko proposed establishing a transition period from December 31, 2007, when, for 13 days, chronology will be carried out simultaneously according to the Julian and Gregorian calendars. In April 2008, the bill was rejected by a majority vote.
The material was prepared based on information from RIA Novosti and open sources
Julian calendar IN Ancient Rome from the 7th century BC e. A lunisolar calendar was used, which had 355 days, divided into 12 months. The superstitious Romans were afraid of even numbers, so each month consisted of 29 or 31 days. New Year started on March 1st.
In order to bring the year as close as possible to the tropical one (365 and ¼ days), once every two years they began to introduce an additional month - marcedonia (from the Latin "marces" - payment), initially equal to 20 days. All cash payments from last year were supposed to end this month. However, this measure failed to eliminate the discrepancy between the Roman and tropical years. Therefore, in the 5th century. BC e. Marcedonium began to be administered twice every four years, alternating 22 and 23 additional days. Thus, the average year in this 4-year cycle was equal to 366 days and became longer than the tropical year by approximately ¾ days. Using your right to enter into the calendar additional days and months, the Roman priests - pontiffs (one of the priestly colleges) confused the calendar so much that in the 1st century. BC e. There is an urgent need for its reform.
Such a reform was carried out in 46 BC. e. on the initiative of Julius Caesar. The reformed calendar became known as the Julian calendar in his honor. The Alexandrian astronomer Sosigenes was invited to create a new calendar. The reformers faced the same task - to bring the Roman year as close as possible to the tropical one and thereby maintain constant correspondence of certain days of the calendar with the same seasons.
The Egyptian year of 365 days was taken as a basis, but it was decided to introduce an additional day every four years. Thus, the average year in a 4-year cycle became equal to 365 days and 6 hours. The number of months and their names remained the same, but the length of the months was increased to 30 and 31 days. An additional day began to be added to February, which had 28 days, and was inserted between the 23rd and 24th, where marcedonium had previously been inserted. As a result, in such an extended year, a second 24th appeared, and since the Romans kept count of the day in an original way, determining how many days remained until a certain date of each month, this additional day turned out to be the second sixth before the March calendar (before March 1). In Latin, such a day was called "bis sectus" - the second sixth ("bis" - twice, also "sexto" - six). In Slavic pronunciation, this term sounded slightly different, and the word “leap year” appeared in Russian, and the elongated year began to be called a leap year.
In Ancient Rome, in addition to the calends, special names were given to the fifth days of each short (30 day) month or the seventh of a long (31 day) month - nones and the thirteenths of a short or fifteenth long month - ides.
January 1 began to be considered the beginning of the new year, since on this day the consuls and other Roman magistrates began to perform their duties. Subsequently, the names of some months were changed: in 44 BC. e. Quintilis (fifth month) began to be called July in honor of Julius Caesar in 8 BC. e. Sextilis (sixth month) - August in honor of Emperor Octavian Augustus. Due to the change in the beginning of the year, the ordinal names of some months lost their meaning, for example, the tenth month (“December” - December) became the twelfth.
New Julian calendar acquired next view: January (“Januaris” – named after the two-faced god Janus); February (“februarius” – month of purification); March (“martius” – named after the god of war Mars); April (“Aprilis” – probably got its name from the word “Apricus” – warmed by the sun); May (“Mayus” – named after the goddess Maya); June (“Junius” – named after the goddess Juno); July (“Julius” – named after Julius Caesar); August (“Augustus” – named after Emperor Augustus); September (“September” – seventh); October (“October” – eighth); November (“November” – ninth); December (“december” – tenth).
So, in the Julian calendar, the year became longer than the tropical one, but by an amount significantly less than the Egyptian year, and was shorter than the tropical year. If the Egyptian year was ahead of the tropical year by one day every four years, then the Julian year was behind the tropical one by one day every 128 years.
In 325, the first Ecumenical Council of Nicaea decided to consider this calendar mandatory for all Christian countries. The Julian calendar is the basis of the calendar system that most countries in the world now use.
In practice, a leap year in the Julian calendar is determined by the divisibility of the last two digits of the year by four. Leap years in this calendar are also years whose designations have zeros as the last two digits. For example, among the years 1900, 1919, 1945 and 1956, 1900 and 1956 were leap years.
Gregorian calendar In the Julian calendar, the average length of the year was 365 days 6 hours, therefore, it was longer than the tropical year (365 days 5 hours 48 minutes 46 seconds) by 11 minutes 14 seconds. This difference, accumulating annually, led after 128 years to an error of one day, and after 1280 years to 10 days. As a result, the spring equinox (March 21) at the end of the 16th century. fell on March 11, and this threatened in the future, provided that the equinox on March 21 was preserved, by moving the main holiday of the Christian church, Easter, from spring to summer. According to church rules, Easter is celebrated on the first Sunday after the spring full moon, which falls between March 21 and April 18. Again the need arose for calendar reform. The Catholic Church carried out a new reform in 1582 under Pope Gregory XIII, after whom the new calendar received its name.
A special commission of clergy and astronomers was created. The author of the project was the Italian scientist - doctor, mathematician and astronomer Aloysius Lilio. The reform was supposed to solve two main problems: firstly, to eliminate the accumulated difference of 10 days between the calendar and tropical years, and secondly, to bring the calendar year as close as possible to the tropical one, so that in the future the difference between them would not be noticeable.
The first task was solved administratively: a special papal bull ordered October 5, 1582 to be counted as October 15. Thus, the spring equinox returned to March 21.
The second problem was solved by reducing the number of leap years in order to reduce the average length of the Julian calendar year. Every 400 years, 3 were thrown out of the calendar leap years, namely those with which centuries ended, provided that the first two digits of the year designation are not divisible by four without a remainder. Thus, 1600 remained a leap year in the new calendar, and 1700, 1800 and 1900. became simple, since 17, 18 and 19 are not divisible by four without a remainder.
The new Gregorian calendar created was much more advanced than the Julian calendar. Each year now lagged behind the tropical one by only 26 seconds, and the discrepancy between them in one day accumulated after 3323 years.
Since different textbooks give different figures characterizing the discrepancy of one day between the Gregorian and tropical years, the corresponding calculations can be given. A day contains 86,400 seconds. The difference between the Julian and tropical calendars of three days accumulates after 384 years and amounts to 259,200 seconds (86400*3=259,200). Every 400 years, three days are removed from the Gregorian calendar, i.e., we can consider that the year in the Gregorian calendar decreases by 648 seconds (259200:400=648) or 10 minutes 48 seconds. The average length of the Gregorian year is thus 365 days 5 hours 49 minutes 12 seconds (365 days 6 hours - 10 minutes 48 seconds = 365 days 5 hours 48 minutes 12 seconds), which is only 26 seconds longer than the tropical year (365 days 5 hours 49 minutes 12 seconds – 365 days 5 hours 48 minutes 46 seconds = 26 seconds). With such a difference, the discrepancy between the Gregorian calendar and the tropical years in one day will occur only after 3323 years, since 86400:26 = 3323.
The Gregorian calendar was initially introduced in Italy, France, Spain, Portugal and the Southern Netherlands, then in Poland, Austria, the Catholic states of Germany and several others European countries. In those states where the Orthodox Christian Church dominated, the Julian calendar was used for a long time. For example, in Bulgaria a new calendar was introduced only in 1916, in Serbia in 1919. In Russia, the Gregorian calendar was introduced in 1918. In the 20th century. the difference between the Julian and Gregorian calendars had already reached 13 days, so in 1918 it was prescribed to count the day following January 31 not as February 1, but as February 14.