m. c. de marco: To invent new life and new civilizations...

On the Kalends of January

Someone on a mailing list asked why New Year’s Day is the first of January instead of some more significant date, like a religious holiday or the solstice. Since I’ve done a fair share of calendar research for my writing and had a little more to do as homework for a class, I decided to answer the question at some length, and also blog it (below the cut).


The Roman year was originally lunar; the named days (Kalends, Nones, and Ides) referred to the new moon, half moon, and full moon. The year started on a new moon in the spring (March 1st, or Kalendae Martii) and went for ten months until December, at which point Rome descended into darkness, confusion, and bribing of the pontiffs to declare the new year at a politically favorable time. Early calendar reforms appended January, February, and an intercalary month to the end of the year, but did not fix the calendar (in the sense of making it deterministic like ours), leaving the significant influence of bribery, political considerations, and rank superstition over the year-to-year determination of dates (and therefore terms of office) firmly in place.

Political events in 153 BCE led to January replacing March as the beginning of Consul terms and, eventually, as the beginning of the year. (So the ultimate source of New Year’s Day was yours truly, in the persons of my rebellious ancestors in Hispania.) Caesar, faced with a calendar that had drifted an entire season away from the solar year, added three months to 46 BCE in order to force the vernal equinox of 45 BCE to occur on the traditional date of March 25th. Note that Christmas likewise falls on the traditional date of the winter solstice (not of the slightly earlier Saturnalia), and only later calendrical drift has obscured this fact.

Now, admittedly, one of Caesar’s months was a scheduled (as much as any of them ever were) intercalary month crammed into the middle of the previous February where it wouldn’t be noticed, but the other two were 33 and 34 days long, respectively, and stuck in between November and December. So 46 BCE was getting pretty long in the tooth come Saturnalia. If Caesar had wanted to move the official beginning of 45 BCE back (that is, forward) to the traditional spring date of March 1st, he would have had to add that coming January and February (this one not intercalated) to the year 46. I’m sure after 445 days of the Year of Confusion everyone was eager to get it over with, even if it meant leaving New Year’s Day pegged forever to the Kalends of January.

The Julian calendar subsequently ran into a few problems: the pontiffs couldn’t count (or were counting inclusively, as was traditional in the horrifying system of counting down to Kalends, Nones, and Ides) and declared leap years every three years instead of four for a while, so that Augustus was forced to correct the calendar by dropping the leap days of 5 BCE, 1 BCE and 4 CE. At that point the Julian calendar became properly fixed.

However, even when properly fixed, the Julian calendar drifts a day every 128 years, so the vernal equinox began creeping away again. Nobody cared all that much. It so happened that at the time of the First Council of Nicaea in 325 CE, the equinox had reached March 21st. For reasons that appear purely anti-Semitic in hindsight, the Council wished to fix the date of Easter (until then something of a free-for-all) while also fixing it apart from Passover in the Jewish calendar. They chose the first Sunday after the first full moon after the equinox. Except for “Sunday,” the concepts involved were not as simple as they sound today, and some controversy persisted. For example, the Church of Rome still reckoned the equinox at its traditional date of March 25th, while the Church of Alexandria went with the then-current astronomical date of March 21st.

Unperturbed, the vernal equinox crept on. Twelve centuries later, when Pope Gregory decided to catch it before it escaped March entirely, he dropped only ten days from the calendar to return it to the now almost universally accepted Alexandrian date of March 21st—even though the Julian calendar had drifted almost thirteen days between 45 BCE and 1582.

The missing three days don’t quite take us back to March 25th because of, again, the drift, which can still cause the time of the equinox to vary by over two full days (and four calendar dates), and is corrected only every hundred years when we drop a Julian leap day for Pope Gregory. You can see a neat picture of the annual quarter-day drift with Julian leap day correction, the remaining fractional drift with Gregorian non-leap day correction, and what hitting the 400-year rule in 2000 did to the pattern, here [Wikipedia].

See how wiggly that winter solstice is? The pontiffs and the Pontiffs all proved themselves completely unqualified to hit a moving feast like that one. Now the Persian calendar starts on the actual day of the vernal equinox, as observed from Tehran, and has real solar (zodiacal) months. Even when fixed (mathematically, as opposed to observed), the seasonal error is never more than about half a day in either direction, as you can see here [Wikipedia again].

The price of pegging your new year to an equinox is calculating 33-year leap-year cycles of 8 leap days, one leap day every four years except for the first one, which occurs only in the 5th year, plus similar 29-year cycles inserted before every three 33-year cycle, and the rare 37-year cycle to handle any remaining drift—or making direct astronomical observations from Tehran. Needless to say, neither approach is pontiff-friendly, but it goes to show it can be done.


Besides the wikipedia links mentioned above and the corresponding articles on the Roman and Julian calendars, a very nice online calendar reference is Claus T√łndering’s Calendar FAQ.

Happy New Year!