Updated: Jun 22, 2021
Today in 1918 the Gregorian calendar was introduced in Russia by decree of the Council of People's Commissars.
This brought another 150million people into line with most of the world. Today's pod looks at the problem of calendar drift with the older Julian Calendar, why the Gregorian Calendar was needed, the people behind it and how it slowly spread around the world.
The Gregorian calendar is the calendar used in most of the world. It was introduced in October 1582 by Pope Gregory XIII as a minor modification of the Julian calendar which had been the legacy of the ancient Roman Empire. There were two reasons modification was needed. First, the Julian calendar assumed incorrectly that the average solar year. that is how long it takes for our planet to orbit the Sun, is exactly 365.25 days long, an overestimate of a little under one day per century. This overestimate lead to the second reason for change, Calendar Drift. The calendar had edged ahead so that the (Northern) spring equinox was occurring well before its nominal date of March 21. This was of particular concern to the church because it was more difficult to calculate the date of Easter. Easter, unlike the other great Christian feast of Christmas, does not have a fixed date, it changes every year. This because the Christian feast of Easter is linked to the Jewish celebration of Passover, which is calculated by a lunar calendar. Passover, which marks Jesus Christs last supper with his disciples, the day before his crucifixion, happens on the night of a full moon after the northern spring equinox. Occasionally now this happens after the second full moon . That is why we can still have early and late Easters, although at present there are some negotiations between Catholic, Orthodox and Anglican leaders to fix the date of Easter. The Gregorian calendar, is a solar calendar with 12 months of 28–31 days each. The year consists of 365 days, with a leap day being added to a February every four years. This leap day, the 29th February, gathers in the ¼ days, and thus counteracts Calendar Drift.
The recalculated Gregorian Calendar was due to work of two men. Primarily the Calabrian doctor Aloysius Lilius who produced an original and practical scheme for adjusting the epacts of the Moon when calculating the annual date of Easter. His work was built on by the German mathematician and Jesuit priest Christopher Clavius, in a closely argued, 800-page volume. He argued that the calendar correction should take place in one move. So when the new calendar was put in use in 1582, the error accumulated was corrected by a deletion of 10 days. The Julian calendar day Thursday, 4 October was followed by the first day of the Gregorian calendar, Friday, 15 October 1582 (and thus the cycle of weekdays were not affected). This change was instituted by papal bull Inter gravissimas dated by Pope Gregory XIII, after whom the calendar is named.
The reform was adopted initially by the Catholic countries of Europe and their overseas possessions. Over the next three centuries, the Protestant and Eastern Orthodox countries also moved to what they called the Improved calendar, with Greece being the last European country to adopt the calendar in 1923. During the 20th century, most non-Western countries also adopted the calendar, at least for civil purposes, with Saudi Arabia following in 2016. Today we remember the decision in Russia by the Council of Peoples Commisars, which brought another 125 million people into a common calendar. Made just after the Bolsheviks grab for power, The Council of People's Commissars had become a government institution formed soon after the October Revolution and evolved to become the highest executive authority of the government of the Soviet Union (see pod of Jan 20 to hear how the church survived the revolution). Most countries now use the Gregorian Calendar as their official calendar. The Chinese Lunar Calendar is still used for celebrations around Asia. Afghanistan and Iran use a Solar Islamic Calendar, Ethiopia a 13 month calendar and Nepal a Hindu Calendar.