Historical Calendar

Julian and Gregorian calendars

By 1500 European countries had generally adopted the Julian calendar of 365 days in a year and 366 days every fourth year. The Julian calendar did however accumulate errors at a rate of roughly one day every hundred years when compared to astronomical events. To correct this, Pope Gregory XIII issued a decree where ten days were dropped, so that 4 September 1582 was followed by 15 September and hence forth a more accurate algorithm was to be used to calculate when leap years should occur. The new Gregorian calendar was not immediately adopted by all countries. The process of adoption took more than three centuries. So after 1582 there were two calendars in use in Western countries. The date on which historical events are recorded to have occurred will differ depending on which country's calendar was the reference.

To see the differing dates for a particular day, choose the a country and year with the drop down menus and the appropriate calendar when be generated. Clicking on any day will show the date of that day in the various countries in the table below the calendar. All the dates will be the same before September 1582, when the Julian calendar was in general use, and they will again all be in agreement after 1923 by which time the Gregorian calendar had been universally adopted.

The highlighted date is Julian Day: 1234567
Here is the date of this day in various countries

The transition from Julian and Gregorian calendars

The calendar for year in which the change from Julian to Gregorian calendar was made is interesting as 10 or more dates will be missing. The changeover years for some of the countries were as follows:
1582 - Italy, Spain
1582 - France (later in the year),
1587 - Hungary
1612 - Prussia,
1700 - Denmark,
1752 - Britain, America,
1918 - Russia.

Sweden's transition was even more complex, they intended to correct the calendar by not having a leap year from 1700 to 1740 thus dropping one day every four years at which time they would have been aligned with the Gregorian calendar. So they dropped the 29 February 1700. But the plan was abandoned before any more leap years were dropped, leaving the country 1 day ahead of the countries using the Julian calendar and still 10 days behind countries using the Gregorian calendar. They got back in line with the Julian calendar by adding two days for the 1712 leap year, making February 1812 thirty days long. Sweden finally adopted the Gregorian calendar 1753.

Julian day number

The ability to assign a number to every day in sequence greatly simplifies the conversion from the different calendar systems. The Julian Day number does just that, with day 0 assigned to be 1 January 4713 BC. The Julian Day number for any day can be seen by clicking on the date, the table then shows the various calendar dates that different countries assigned to that day.

Differing dates of historic events

The Great Fire of London is recorded as starting on 1666 September 2 (see Pepys' Diary), Julian day number 2329809. In France, they would have seen the smoke rising across the channel on September 12, since France had changed to the Gregorian calendar (skipping 10 days at the change-over) and England had not.

The Russian Bolshevik Revolution is celebrated in Russia as the October Revolution. The Russian revolutionaries captured the seat of government in Petrograd on 25 October 1917 according to their calendar, which was still the Julian calendar, but it was reported in New York as having just happened on 9 November 1917. The news reached the USA the next day which was November 8 in USA, since they were using the Gregorian calendar. The story was published in the NY Times on the November 9 [EXTREMISTS RISE TO POWER IN RUSSIA, NYT 1917 Nov 9].

To see this difference on the calendar, use the drop down menus at the top of the calendar, select the country: RUSSIA, and the year: 1917, click on October 25. The table of dates in various countries shows that all other countries name this day 1917 November 7. That's why the news of the revolution reached the USA on November 8, only hours after the event, not after the apparent 13 day delay.