The first calendars were created in the Bronze Age and were based on the phases of the moon. The waxing and waning of the moon was much easier to track for early humans than the slow, steady path the earth takes around the sun - however, the lunar year is much shorter than a true solar year. The moon takes 29.53 days to fully orbit the earth, making a lunar month much shorter than an average one, and meaning that a year measures just 354.36 days. This system was suitable to keep track of a vague idea of the seasons for agricultural purposes, but over time a more accurate calendar was needed.
The Ancient Egyptians based their first calendar on the flooding of the Nile, which was surprisingly accurate as it occurs around the same time every year. The Nile was vital to life and its flood season fell between the seasons of growth and harvest that made up their year.
Eventually, Egyptian astronomers began counting the year according to Sirius, the brightest star in the sky, and reached a more accurate 365 days. During his time in Egypt, Julius Caesar noticed how useful it was to have an ‘official’ calendar and he decided to create his own – the ‘Julian’ Calendar. The Julian Calendar used a year of 365 days and just as we have today, there was a leap year every four years. However it was far from perfect, and was actually losing about ten minutes a year. Ten minutes isn’t a huge amount of time, but it adds up - especially over 1.5 millennia.
The mistake was first caught by an English friar named Roger Bacon in the thirteenth century, who immediately sent a messenger to Pope Clement IV. If the mistake was left unchecked then eventually the seasons would switch entirely but Bacon’s message to the Pope presented a much more pressing matter to the Catholic Church - this meant that they were celebrating important feast days, like Christmas and Easter on entirely the wrong date. Bacon and the Pope were academic acquaintances so while in any other age he might have been branded a heretic for criticising the church, his theories were greeted with a request for a more substantial piece of research and a suggestion of how best to go about fixing the issue. In response Bacon set about compiling his life’s work into a magnum opus and suggested that a day be dropped from the calendar every 125 years to correct the drift but by the time he finished the Pope had died and the new head of the church wasn’t so receptive to criticism. Bacon was eventually thrown in prison and when he emerged in his eighties he had lost all credibility and the incorrect calendar lumbered on.
By 1582, the Julian calendar had caused a drift of about ten days and this issue was becoming noticeable. In the Catholic Church the date of the Spring Equinox is used to calculate the date of Easter, the anniversary of the resurrection of Jesus Christ. Under the Julian Calendar the date was wrong and the Church had incorrectly set it at the 21st of March when in reality the spring equinox changes year by year. Due to the drift in the Julian calendar by the sixteenth century the equinox was now falling around the 11th of March - far too early. It was this issue in particular which led to the calculation of a newer more correct calendar named the Gregorian calendar to replace the old style. Named for Pope Gregory XIII, the calendar was made to correct the mistakes of the Julian calendar, and put the official year back in time with the solar year. To do this meant removing ten days and Thursday October 4th 1582 skipped directly to Friday October 15th.
The change was accepted as quickly as possible across the Papal States but the church had no power to immediately force everyone to adopt the Gregorian calendar. Most of Europe accepted the change within the following two centuries, with Protestant counties slower to accept this Catholic Calendar. Protestant Britain (and Ireland by extension) eventually accepted the change in 1752 – by which point eleven days had to be removed. Here in Ireland the was passed in 1750 to mirror the English version and stated:
‘whereas the calendar now in use throughout all his Majesty’s British dominions, commonly called The Julian Calendar, hath been discovered to be erroneous, by means whereof the vernal or spring equinox, which at the time of the general council of Nice in the year of our Lord three hundred and twenty-five happened on or about the twenty-first day of March, now happens on the ninth or tenth day of the same month; and the said error is still increasing, and if not remedied would in process of time occasion the several equinoxes and solstices to fall at very different times in the civil year’
Many people were unhappy and suspicious with this change, particularly because all the feast days suddenly moved and also because there was a mistaken belief that rather than simply being just an administrative change they had lost eleven days from their own lives! There are reports of ‘Calendar Riots’ happening in Britain, but this seems to be simply an urban myth from the Georgian period as no such riots can be found in records. Their biggest concern was that they would have to pay their taxes and rents eleven days early!
The very last country to adopt the ‘new style’ was Greece, who finally accepted the Gregorian Calendar in 1923! Learn all about this quirky moment in time and more when the ‘Museum of Time’ opens at Greyfriars!