People in the Western world have celebrated January 1 as the dawn of a new year for more than two millennia. We can credit the establishment of this date to the Roman emperor, Julius Caesar. After years of frustrating inaccuracies in time keeping, Caesar decreed that changes would be made to the old Roman lunar-based calendar system.
Introduced around the seventh century B.C., the Roman calendar attempted to follow the lunar cycle, but it frequently fell out of phase with the seasons and had to be corrected. More importantly, the pontifices, the Roman body charged with overseeing the calendar, regularly abused its authority by adding days to facilitate private political interests.
To accomplish this rather monumental task, Caesar enlisted the help of Sosigenes, an Alexandrian astronomer. Sosigenes suggested a modified 365-day calendar with the addition of an extra day every fourth year (a leap year). Interestingly, the idea wasn’t original to Sosigenes. A similar leap-day scheme had been tried in Egypt in the third century B.C. by Ptolemy III Euergetes, but it was met with great resistance.
Under Sosigenes’ scheme, a year was calculated to be 365 and 1/4 days. To get things started on a correct footing, Caesar added 67 days to 45 B.C., making 46 B.C. begin on January 1, rather than in March. Shortly before his assassination in 44 B.C., Caesar also changed the name of the month Quintilis to Julius (July) after himself. Years later his successor, Caesar Augustus would rename the month, Sextilis, after himself.
Improved as Sosigenes’ calendar was, inaccuracies remained. Through a misunderstanding of Sosigenes’ directives, leap days were at first inserted every three years rather than every four — an error corrected during the reign of Augustus.
We also know that Sosigenes failed to accurately calculate the precise length of a solar year. The correct value for the solar year as 365.242199 days, not 365.25 days — as Sosigenes had reckoned. Thus, an 11-minute-per-year error added seven days by the year 1000 A.D. — an error that grew to 10 days by the mid-15th century.
By 1582, it was again time for an official adjustment to the dominant calendar scheme. Pope Gregory XIII commissioned Jesuit astronomer Christopher Clavius to devise a new calendar. The calendar was ordered to advance by 10 days. Clavius also introduced a new method to avoid future errors: century years such as 1700 or 1800 would no longer be counted as leap years, unless they were (like 1600 or 2000) divisible by 400. While a bit clunky, the system works and is still our official method of time-keeping.
Interestingly, the Gregorian calendar year differs from the solar year by only 26 seconds. Most of us won’t notice the difference though, since this only adds up to a single day’s disparity every 3,323 years.
Of course, there will always be laggards and nay-sayers. Many European Protestant countries ignored the promulgation of the Gregorian calendar. It wasn’t until 1698 that Germany and the Netherlands agreed to adopt the Gregorian scheme. Great Britain held fast until 1751. Russia relented only after the 1918 revolution. Greece remained Julian until 1923. Even now, some Orthodox churches continue to follow the Julian calendar — which is presently 13 days behind the Gregorian.
This likely goes to the broader point that some folks will fight about almost anything. It’s not that the dominant calendar system isn’t important. Certainly it is, but this millennia-long squabble shows the absurd extent of our willing intransigence. Perhaps as we look for New Year’s resolutions, greater flexibility and openness to reason might be worth consideration. Whatever your system of reckoning — Happy New Year.