Last week a friend of mine pointed out that Rosh Hashanah comes early this year. She went on to bemoan the fact that the first day of Hanukkah falls on the day before Thanksgiving*: a result of the disjunction between a lunar and solar calendar over the long haul.**

The discussion reminded me of a topic that I’ve been wanted to talk about here for a long time–calendars and history.

Dates and calendars can be a vexatious issue for the historian, unless you write exclusively about the Western world post-1800. For the rest of us, there is always a question of just what calendar was/is in use. Here are a few examples of how a calendar can give a historian a headache :

1. The Gregorian calendar, also known as the Western calendar or the Christian calendar, is the international standard today.*** It was first introduced in 1582 in Italy, Poland, Portugal and Spain–replacing the earlier, less accurate Julian calendar. (itself an effort to reform the Greek and Roman calendar.) In order to make the calendar line up with the seasons, the powers that be dropped ten days in October, 1582. **** Not everyone went along with the change–either because they disagreed or because the lack of mass media as we know it meant they didn’t hear about it. To add to the confusion, it took time for other Western countries to make the change: Great Britain and its American colonies didn’t accept the Gregorian reform until September, 1752. By then the difference between the Julian and Gregorian systems had increased: the British lost eleven days instead of ten with the change, giving new meaning to the phrase you snooze, you lose. Once again, sticks in the mud and those living in the sticks took a while to catch up. Assuming that everyone made the switch within ten years, there is a period of roughly 180 years when a historian can’t be sure if the date on a document is under the Julian or Gregorian system. Most of the time it doesn’t matter whether something happened on December 1 or ten days earlier; sometimes it does.

2. The Mayan calendar got a lot of press in 2012. But the Mayans weren’t the only culture to have their own calendar outside the Roman/Christian calendrical system. Every culture from Babylon on had its own calendar. Some were based on solar cycles. Some were based on lunar cycles. Some on a complicated combination of the two. More important from the historian’s point of view, each calendrical system needs a way to count the passage of years. Most count from an initial epoch tied to a historical or legendary event.***** A few count years in cycles. Others don’t count years at all, but name each year after an event that characterizes the year. In order to know what year an event happened in the modern calendar system, we have to know how the system in question relates to ours. Building the calendar of a different time and place from inscriptions, coins and documents is a painstaking process; finding a moment at which it connects to our own requires luck as well as skill.

3. The past isn’t the only place to have a different calendar. Just because the Gregorian calendar is the international standard doesn’t mean that it’s the only one people are still using. Roughly 40 calendar systems are in use around the world today. The lunisolar Hebrew calendar is not only the liturgical calendar of Judaism, but the official calendar of Israel. The purely lunar Islamic calendar does not track with the seasons and dates from the Prophet’s flight to Mecca–2013 CE is 1434 in the Islamic calendar. The Republic of India had its own calendar reform in 1952, trying to find a common ground between the 30 some Hindu calendars then in use. The Indian National Calendar is a twelve month cycle that does not match the months of the Gregorian calendar and is counted from the Saka era, a traditional epoch of Indian chronology. It’s 2013 in Chicago, but it’s 1935 in New Delhi. ****** Then there’s the Chinese calendar, the Buddhist calendar…..

In short, calendars are cultural constructs derived from human observation of the natural world–not an immovable natural fact.

What day is it? It depends.

*Or at least speculated about the impact on retailers.

**I’m not going to try to explain how this works, but over time the difference between 12 solar months and 12 lunar months adds up. Instead of adding a leap day every four years, the Jewish calendar adds an extra month seven times over the course of a nineteen year cycle. This is necessary to keep the calendar in line with the seasons.

***Another by-product of Western imperialism

****Think about how much people complain about losing one hour when Daylight Savings Time goes into effect in the spring. Imagine the complaints about the loss of Ten Whole Days.

***** The Gregorian calendar counts from the birth of Christ–or at least from an inaccurate calculation of the birth of Christ by sixth century scholar Dionysius Exiguus, who did the best he could with the information he had. Johannes Kepler later corrected the date to what is now 4BCE. Did I mention that dates and calendars are vexatious things?

******Though not everywhere in India. Some regions still use other calendars. Calendar reform? What reform?