Ordering CHAOS

How long is the solar year? If you want to be precise about it, according to NASA (the U.S. National Aeronautics and Space Administration, which among its other accomplishments, put men on the moon), it is 365.2422 days in length ¹ . The Gregorian Calendar, in use throughout the world, is able within a hairsbreadth, of hitting that number. Likewise, the normal calendar cycle of 30 and 31 day months to which we have become accustomed and which decrees a leap year addition of one day to February every four years, usefully approximates both. Indeed, that four-year cycle that governs our daily lives will serve without adjustment until the year 2100 (and even that adjustment will only mean skipping the otherwise scheduled February 29 leap day). 

In the article entitled “The Brain of a Perpetual Calendar”, we turn to the cleverness of how Blancpain’s watchmakers have mechani­cally created a mechanism that follows the complexity of months that vary in length between 28 and 31 days, and in the story entitled “A Rainbow of Perpetuals”, we take a tour of Blancpain’s current perpetual offerings. First, however, a voyage through time to learn how our calendar evolved from its beginnings in the era of the Roman Empire.  

Before decrees issued by Emperor Julius Caesar, chaos reigned with the then Republican Roman Calendar to the degree that one of the vital purposes of having a calendar, reliably predicting the seasons for farming, was largely lost. The Republican Calendar ceded to politicians the power to add days and occasionally even months to the year. All too often the deci sions were partisan, with additions of months when allies could be advantaged and refusals to add when it would serve to injure opponents. It is easy to understand why, over time, these irregular practices of calendar insertions undermined the real purposes of having a yearly calendar at all. Indeed, by 40 B.C. the chaotic Roman Republican Calendar was already three full months out of kilter from the solar calendar. 

Guided by Sosigenes, an Alexandrian astronomer, Julius Caesar sought order when in 46 B.C. he instituted a new and, most importantly, a predictable and regular system. Now known as the Julian Calendar, it calculated the year to be 365.25 days in length. Essentially laying the groundwork for what we know today, it was constructed with months of 30 and 31 days, and a February of 28 days. To deal with the assumption of an additional quarter day, a leap day was added onto February every four years. 

The underlying assumption of a 365.25 day year was not quite perfect. For example, the date of Easter keyed to March 21 ² was drifting late at a rate of one day every 130 years. With the stated goal of moving the date of Easter earlier, Pope Gregory XIII issued a “Bull” (a formal proclamation) “Inter Gravissimas” which instituted the calendar we know today as the “Gregorian Calendar”. The proclamation left in place the sequence of 30 and 31 day months and the February leap years occurring every four years. The change, however, ­ eliminated leap years for those years divisible by 100 unless the year was also divisible by 400, when a regular leap year would occur. Thus, for example, the year 2000, although divisible by 100 was also divisible by 400, triggering the “exception to the exception” resulting in the addition of a regular leap year day to the month of February 2000. For the year 2100, divisible by 100 but not by 400, February will have but 28 days, skipping the leap day that would otherwise occur according to the standard four-year cycle. Keep in mind the miniscule magnitude of the change in the assumed average length of year arising from the replacement of the Julian Calendar with the Gregorian Calendar. The elimination of three leap year days every four hundred years in the Gregorian Calendar from the Julian year of 365.25 days shortened the average year length to 365.2425 days or said another way a change of 0.0075 days or one day every 133.33333 years! That is not to say that the Gregorian Calendar perfectly matches the actual solar year; the Gregorian average year is in fact 0.0003 days too long, producing an error of one day every 7,700 years! 

The transition from the Julian to ­ Gregorian Calendar was far from either smooth or uniform. The Papal Bull had legal effect only in those regions subject to the ­ Vatican’s jurisdiction in 1582: Spain, Portugal, Poland, and most, but not all, of Italy. Wider adoption in the West gradually took place over the following two and a half centuries. Both religion and stubbornness played roles in prolonging this transition. Perhaps the starkest illustration of pockets of resistance took place in a single country: Switzerland. It took more than 200 years for there to be a single calendar in the  country, beginning with the first embrace of the new calendar in Basel in 1583, and the last in mixed religion Graubünden ³ . In England, which changed in 1752, it became common for citizens to specify which date was being used in documents where the notation “O.S.” (old style) signified a Julian date and “N.S.” (new style) signified a Gregorian date. 

Some of the struggle coming to terms with converting to the new calendar came from the need to account for the slow drift in dates that had accumulated over the 17 centuries that the Julian Calendar had been in force. When the Papal Bull came into effect on Thursday, October 4, 1582, this centuries-long date drift was corrected by declaring a date jump for the “next day,” Friday, which instead of being October 5 was proclaimed to be October 15, 1582. For some, this transition jump was amusing. When the Eastern United States changed (in parallel with England) on September 2, 1752 there was a similar dislocation: thus, September 2 was followed the next day by September 14, 1752 with Benjamin Franklin observing: “It is pleasant for an old man to go to bed on September 2 and not have to get up until September 14”. 

These contortions aside, the two hundred year history of mechanical perpetual calendar watches has rightly focused upon the four year cycle akin to that of the Julian Calendar. That cycle only requires a manual intervention but three times every 400 years and, even then, with at least a 100 year gap between adjustments, thus fully serving the purpose of a perpetual calendar watch. Indeed, the very nature of a mechanical mechanism, mandating periodic servicing, will intercede far more often than the 100 year exceptions of the Gregorian cycle. Thus, day to day, year to year, a timepiece that fully implements the variations in the length of 30 and 31 day months and the regularly occurring sequence of Februarys, practically speaking, is a perfect calendar companion for its owner. How this is done is set out in “The Brain of a Perpetual Calendar”. 

_{¹ Said another way: 365 days, 5 hours, 48 minutes and 45.25 seconds.} 

_{² The date of Easter is determined to be on the first Sunday on or after the ecclesiastical full moon after March 21.} 

_{³ The Graubünden calendar history is extraordinarily tumultuous. To begin with, the population was split between Catholics and Protestants. That division combined with the absence of a central government led to the lack of a uniform calendar. Catholic parishes adopted the Gregorian Calendar between 1623 and 1624. The transition in Protestant communities spanned the period 1783 to 1812. Indeed the 1812 last holdouts only capitulated after an order from the Grand Council which carried a penalty of a fine. That earned those communities the distinction of being the last municipalities in Western and Central Europe to adopt the new calendar.}