The calendar was introduced into public practice on the basis of the reckoning of time by the Egyptians as early as the fourth millennium BC. Since ancient times, they have developed the initial forms of astronomy, closely related to the needs of agriculture, the determination of the seasons, periods of economic work associated with the floods of the Nile.
The Egyptian year, like ours, was 365 days, but they did not have a leap year. The Egyptians considered the beginning of the new year on July 19 of our calendar, the day when the bright star Sirius appears on the eastern horizon at sunrise.
By the personal decree of Peter I, a new chronology began in Russia in 1699. Peter I changed the previous custom, according to which the chronology was dated from the so-called "creation of the world", arbitrarily assigned to 5, 508 BC. According to the pre-Petrine chronology, our year 1963 would have been the year 8471.
The main unit of the solar calendar is the year, which originally had unequal duration among different peoples (for the Egyptians - 365, for the Romans - 355, etc.). The reform of the solar calendar was carried out in 46 BC under Julius Caesar at the suggestion of the astronomer Sozigen. In the Julian calendar, out of every 4 years, 3 years have 365 days and 1 year, the leap number of which is divisible by 4, has 366 days. The average length of the year turns out to be 365.25 days, which is 0.0078 days longer than the tropical year (the period of changing the seasons); for 400 years, this gives a delay of the beginning of the calendar year by 3 days. In this regard, in 1852, Pope Gregory XII made a new calendar reform, skipping 11 days (after October 4, October 15 was immediately counted) and stop counting as leap years those years whose numbers are divisible by 100, but not divisible by 400 (for example, the year 1700 ). The difference between the Gregorian and Julian calendars is growing: in the 17th century it was 10 days, in 18-11, in 19-12 days.
In 1918, when the difference between the Gregorian calendar (new style) reached 13 days with the Julian calendar (old style), we introduced the Gregorian calendar on February 14 (February 1, old style).