The first draft reform of the Julian calendar was submitted as early as in the 14th century. The Catholic Church dealt with the reform, presenting it at the ecumenical councils of Constance and Basel. At the Council of Basel, St. 1435 r. the following were discussed:. in. on the project of Mikołaj z Kuza, recommending that the entire week of the end of May should be omitted from the calendar 1439 r. However, it was not approved.
The case was revived in 2 mid-15th century, when is the famous German astronomer, Jan Regiomontanus, he announced, that only in recent years 60 years, the date of Easter was in 30 ill-designated cases. Pope Sixtus IV (1414—1471) he then instructed Regiomontanus to design a new calendar. Unfortunately, death of the astronomer in 1476 r. she stopped finishing the work.
Many astronomers also worked on the reform of the calendar during the pontificate of Leo X. The V Lateran Council, convened on his initiative in 1512-1516, asked for help in this matter from the most famous universities - in Paris, Vienna, Tübingen, Louvain and Krakow. And this time there was no reform. It was made only during the pontificate of Pope Gregory XIII (1502—1582). Of the numerous projects - presented to a special commission, appointed by the Pope in 1576 r. - one was selected, undoubtedly the best, being the work of a professor of medicine, Alojzy Lilia, then it was sent to the universities, princes and archbishops for their opinion. The opinion was positive. 21 II 1582 r. So the pope issued a bull, recommending admission (starting of 4 X that year) new calendar.
New calendar, later called Gregorian, removed 10 days since the Council of Nicaea, restoring the spring equinox to the day 21 III (before the reform, it fell on 11 III). It was done by leaving those days like this, that after 4 X 1582 r. followed 15 X. In order to prevent a future shift of the spring equinox, it was decided to leave 3 leap days during 400 lat. The principle has been established, that of the years containing the total number of hundreds (np. 1600, 1700, 1800, 1900 itd.) only these will be leap, which are completely divided by 400. A year was therefore a leap 1600, while the years 1700, 1800 i 1900 were ordinary years. In addition, a normal leap year was adopted according to the rule established in the Julian calendar (every fourth year divided completely by 4). In this way - without actually departing from the Julian calendar - the average length of the calendar year was more similar to the astronomical one, amounting to 365 days, 5 hours, 49 minute i 2 seconds, tj. 365,2425 day.
The Gregorian year is therefore longer than the tropical year only by 26 seconds. As a result - only after 34 centuries (exactly - after 3 360 lat) a difference will form from the Gregorian reform 1 day (but it's worth adding, that in the year of the reform this difference was 24 seconds, so it was smaller; the current difference is due to this, that the length of the tropical year is slightly shortened - by 5,3 seconds to 1000 lat).
Of course, the months and their internal distribution remained the same. Except February, which has finally been stabilized: ma 28 days in an ordinary year or 29 in a leap year.
Time count according to the new calendar has been given the name of the new style (The new blogs), unlike the Julian calendar, known as the old style (ancient blogs).
But - as is the case with reforms - it was not greeted with enthusiasm everywhere.
• The earliest introduction of the Gregorian calendar was in Italy, Spain, Portugal and Poland. In these countries - as recommended by the papal bull - it came into force on 15 X (according to the new style) 1582 r. In Poland - with the exception of the eastern borderlands and Livonia - he was accepted without resistance. However, some scholars have criticized him.
• Two months later it adopted the France calendar. After 9 XII happened directly here 20 XII 1582.
• W 1700 r. the Gregorian calendar was adopted by Protestant Germany - under the name of the "corrected calendar".
• W 1752 r. — Anglia (not without support; there were even street demonstrations in London on this occasion).
• W 1753 the calendar was adopted by Sweden.
• W 1873 - Japan.
• W 1916 - Bulgaria, but… modified and as "new eastern calendar", anyway - a bit more precise than the Gregorian (which was no longer an art, having a calendar ready and the latest astronomical calculations). The year of this calendar differs from the tropical o 0,000024 day, gregoriańskiego - or 0,0003.
Romania also accepted him (w 1919) and Greece (w 1923).
• W 1917 r. the Gregorian calendar was adopted by Turkey, a w 1918 - Russia.
It's safe to say, that the Gregorian calendar gained international significance. It is used in most countries of the world. China also adopted him after World War II (w 1949). However, some countries still use different calendars, sometimes alongside the Gregorian calendar.