The Year That Only Had 355 Days

In modern times, we’re very comfortable with the idea of occasional small tweaks to the length of a year. These mostly occur in a very programmatic way, through the leap year rule that adds an extra day to every fourth February (except in three of every four century years), but there are also smaller, less predictable changes. Every now and then, we add a “leap second” at the end of a year, so that in the Greenwich time zone, the clock on December 31 will tick from 11:59:59 to 11:59:60 before going to 12:00:00 on January 1. These are necessary to keep the calendar in synch with the rotation of the Earth, as determined by the International Earth Rotation and Reference Systems Service, who closely track the apparent motion of astronomical objects to measure the slowly changing rate of rotation of the Earth.

In the more distant past, however, we’ve occasionally had more dramatic changes to the length of a year. The year 1582 was particularly notable, in that Thursday, October 4 was followed by Friday, October 15. At least, it was in a large swath of Europe controlled by countries allied with the Roman Catholic Church.

The event that led to this drastic shortening was the implementation of the Gregorian reform of the calendar, which brings the average length of a year as tracked in Western countries (365.2425 days) into closer agreement with the tropical year, the time between one solstice or equinox and the next (365.24217). This highlights two of the themes that recur in the history of timekeeping that I’ve been discussing here in the run-up to next week’s release of my new book on the subject. The first, as noted in the post linked at the start of this paragraph is the incredible depth of the history of timekeeping. The roots of the Gregorian calendar can be traced back to something like 2700 BCE, when the Egyptian civil calendar was implemented, a span of time that allowed priests and astronomers to directly observe the Sothic cycle and confirm that a 365-day year (the original Egyptian civil calendar) was too short, and a 365.25 day year (the Julian calendar implemented in Rome around 8 BCE) too long.

The second important theme illustrated by the Gregorian reform is the essentially arbitrary nature of time, which physics tells us is not a single well-defined universal quantity. While this is a bit of a conundrum, philosophically, it’s useful politically, allowing us to implement time zones and daylight saving time through the political process.

In the case of the Gregorian reform, along with implementing the new calendar to slightly shorten the year, the Papal authorities decided to move the year slightly, so that the March equinox would fall around the 20th of the month. This was chosen as a compromise: the primary theological reason for the change was to simplify the calculation of the date of Easter, so that it would be falling at the same point in the astronomical year that it had in the time of Jesus. That would’ve argued for putting the equinox on the 14th of the month, but the Church had recently printed and distributed an enormous number of new missals and breviaries giving the key dates of the ecclesiastical year for the next several years, so they opted to put the equinox on the 21st and save the cost of replacing all of those.

The ten days to be dropped by Papal fiat were chosen to be in early October because there were no significant feast days in that span, another practical compromise. The implementation was not entirely smooth or uniform, either— the reform was ordered in February of 1582, and it was a struggle to get enough of the new calendars printed in time. The initial proclamation gave Antonio Lilius, the brother of the late Calabrian doctor who devised the Gregorian reform, the exclusive right to publish new calendars, but that was rescinded in September to boost printing capacity. The adoption was also hampered by the Protestant Reformation then roiling Europe: only the staunchly Catholic monarchy in Spain and the Polish-Lithuanian commonwealth actually made the switch at the appointed time, with other Catholic nations trickling in over the next several years.

Protestant nations at the time mostly refused to acquiesce to a system promulgated by the Pope in Rome, so for the next couple of centuries, many dates are doubled, reported both “old style” and “new style.” Isaac Newton, for example, marked his birthday as falling on Christmas Day, December 25, 1642 under the old style, but many sources now give it as January 4, 1643 in the new.

Britain, as a Protestant nation, did not make the switch to the Gregorian calendar immediately, though they came tantalizingly close, thanks to a proposal from Elizabeth I’s court astrologer John Dee. Dee’s proposed change, which gave an English gloss to the Gregorian reform, was blocked by the Archbishop of Canterbury. The change finally came in 1752, again for reasons of political convenience: Philip Stanhope, the Earl of Chesterfield, was annoyed at having to convert between dating systems during a diplomatic posting on the continent, so vowed to clear it up on his return.

By the time Stanhope and his allies managed to work the reform through Parliament, they needed to drop 11 days, not 10— 1700 had been a leap year in the Julian system but not the Gregorian— meaning that September 2, 1752 was followed by September 14 in areas under British control. This seems to have gone remarkably smoothly, all things considered, though it was briefly contentious enough for “Give Us Our 11 Days” to be immortalized as a political slogan in William Hogarth’s satirical painting series “Humours of an Election.”

The last European holdout was Tsarist Russia, which only switched after the revolution in 1917 brought the communists to power, at which point they needed to drop 13 days. The Gregorian calendar is now pretty much universally agreed upon for international trade purposes, though a few countries officially use other systems internally, for political or religious reasons. The convoluted history of its adoption is a nice reminder, though, that all of this is fundamentally arbitrary: we agree on this system of numbering days because it’s convenient to do so, but could just as easily choose a different system altogether, even if it means a drastic shortening of a year here or there.