Why does humanity need a calendar? This is a question that does not require an answer. Without it, people would get confused over time, completely unaware of when certain events on the planet happened, are happening or are planned in the future. Not only years and months, but even days, minutes, seconds need an account. For this, the ancients came up with a systematization of time. There were a great many different calendars on the old woman Earth throughout the history of mankind.
One of them was Julian. It was used by Europeans until 1582, and after it was replaced by order of Gregory XIII - the Pope - on the Gregorian calendar. And the reason turned out to be compelling: the Julian date sinned with inaccuracy. Why was the old calendar imperfect, and how did you manage to solve this problem? This will be discussed.
Tropical year
The calendar is accurate when it corresponds to natural astronomical cycles. In particular, the year should coincide with the period during which the Earth makes a complete revolution around the Sun. According to astronomical data, this period of time is approximately 365 days and 6 hours. This, the so-called tropical year, laid the foundation for the reckoning. As you know, the usual year of our modern calendar has 365 days. Consequently, every four years another day runs up. This is where February 29 comes from in leap years. They do this to even out the tropical and calendar years.
At the time of Gregory XIII, no one knew about the periods of the Earth's rotation, but there were methods for determining calendar accuracy. It was very important for the ministers of the Church that the spring equinox, according to which the time of the onset of Christian Easter was determined, should come on the same day, that is, as it should be, on March 21. But once it turned out that the indicated date in the Julian calendar differs from the tropical one by 10 days. And the spring equinox falls on March 11th. To eliminate this discrepancy, we introduced a calendar, just named after Gregory XIII.
Roman calendar
The predecessor of the Julian was the Roman calendar, developed in ancient times on the basis of knowledge borrowed from the priests of Ancient Egypt. The year, according to this reckoning, was counted from January 1. And this coincided with the Julian date of its beginning and with later European traditions.
However, in those days they still could not count astronomical cycles with great accuracy. But because the year, according to the Roman calendar, consisted of only 355 days. The ancients noticed this discrepancy in order to align their dates with the vernal equinox; at the end of February, additional months were inserted as necessary. But decisions on this by the college of Roman priests were not always made carefully, often adjusted for political rather than astronomical considerations. That is why significant errors occurred.
Calendar Reform of Julius Caesar
A more accurate calendar, named Julian in honor of Julius Caesar, was compiled by Alexandrian astronomers and adopted in ancient Rome in 45 BC. He synchronized the natural cycles and the human system of calculating the years, months and days. The Julian date of the vernal equinox now corresponded to the tropical calendar, and the year was 365 days. Also, with the introduction of the new reckoning, an additional day appeared, which appeared on the calendar every four years.
And he ran up from those already mentioned, not previously considered by the ancients, astronomical six hours necessary for the Earth to complete its rotation around the Sun. So there were leap years and the Julian date of the extra day in February.
Where did the error come from
But if the accuracy was restored in those days, and the calendar of the ancients became very similar to our modern one, how did it happen that in the time of Gregory XIII the need for reform arose again? How did the error of the Julian date of the vernal equinox make as much as 10 days?
Everything is very simple. The extra 6 hours, of which once every four years an extra day of leap years runs, in a more accurate measurement, as it turned out later, is only 5 hours 48 minutes and about 46 seconds. But this time period varies, more or less is made from year to year. These are the astronomical features of the rotation of our planet.
These 11 minutes and a few seconds were completely invisible for a long time, but after centuries, they turned into 10 days. That's why the ministers of the Church in the 16th century sounded the alarm, realizing the need for reform and translation of Julian dates on the days of the new calendar.
Gregorian calendar recognition
By order of the Pope in 1582, in October after the 4th day, the 15th immediately came. This brought the church calendar into line with natural cycles. Thus, the dates of the Julian calendar were translated into the new Gregorian.
But such changes were not accepted by all and not immediately. This was due to religious considerations, because just at that time the Protestant anti-Catholic movement was gaining strength. Therefore, the adherents of this movement did not want to obey the decrees of the Pope. Calendar reform in Europe has stretched for several centuries. In England and Sweden, a new system of chronology was adopted only in the middle of the XVIII century. In Russia, this happened even later, after the October Revolution in January 1918, when a decree signed by V.I. Lenin.
Orthodox calendar
But the Orthodox Church in Russia, which at one time did not obey the Pope of Rome, did not want to agree with the decree of the Soviet government. Therefore, the Christian calendar did not change even in those days. His reform has not yet been carried out even to this day, and church holidays continue to be celebrated in the so-called old style. The Serbian and Georgian Orthodox churches, as well as Catholics in Ukraine and Greece, support the same traditions.
The Gregorian date can be translated into Julian, subtracting 13 days from the accepted date. That is why Christmas in Russia is celebrated not on December 25, but on January 7, and the old New Year comes almost two weeks after the calendar.