An interesting fact: until 1918, Russia lived on a different calendar than most European countries. Our country kept chronology according to the Julian calendar, and Europe according to the Gregorian calendar.
What was the difference? In the Julian calendar, every fourth year is recognized as a leap year. It turns out that the calendar year is 11 minutes longer than the astronomical one and an extra day is formed every 128 years.
In the Gregorian calendar, every fourth year is also considered a leap year, except for years divisible by 100 in those cases when they are not divisible by 400. Extra days are formed only for 3200 years.
At the beginning of the 20th century, the difference between the two calendars was 13 days.
Back in 1830, the Russian Academy of Sciences was in favor of switching to the Gregorian calendar. The issue was discussed for decades, but the rulers of Russia were in no hurry with a final decision, since the Russian Orthodox Church opposed the innovation. In this case, the liturgical annual cycle was violated.
In 1899, the Russian Astronomical Society again returned to this issue. A special "calendar commission" was created, which worked until 1911.
But the final decision on the transition to the "new style" was made only after the revolution. The decree "On the introduction of the Western European calendar" was adopted by the Council of People's Commissars of the RSFSR on January 24, 1918.
The transition to a new chronology took place on January 31, 1918. Immediately after that day came the 14th of February. As the newspapers of that time wrote: "From that moment on, the Russian Soviet Republic was attached to the family of cultural peoples of the whole world."
Interestingly, confusion over historical dates has begun since then. The fact is that often when translating the date of a historical event to a new style, 13 days are simply added.
But the difference between the two calendars was not always the same. For example, in the 17th century it was 10 days, in the 18th it was already 11, in the 19th - 12 days.
It is believed that one of the reasons for the defeat of the Russian-Austrian army in the battle of Austerlitz in 1805 was that the Allies used different calendars and this led to errors in joint actions.
And one more curious fact: it is generally accepted that the Battle of Kulikovo took place on September 8, 1380. But this date is indicated in the Russian annals according to the Julian calendar. At that time, the difference between the two calendars was 8 days. Therefore, the date of the great battle in the new style is September 16, 1380.