Tomorrow is the beginning of the new year in the Jewish Calendar. Though I don’t claim to be an expert in the workings of that calendar, I know that even that first sentence is problematic. What do I mean by “tomorrow”? Typically it might mean the 24 hour period following the next midnight. That doesn’t work here because in this case, the day ends and the new day begins at sunset. On different calendars those little squares that often indicate days, might not mean the same thing. There is another problem with that first statement but I’ll have to get to that later. That just this one simple sentence can be problematic in two different ways, says something about not taking things for granted.
There are many other factors besides when the day changes that go into the workings of a calendar. We tend to take them so much for granted that it is easy to assume that whatever date we look at, it must mean exactly what we think it means. Taking a look at another calendar, is like when one first realizes that there are languages beyond your native language. I don’t remember when I first realized that languages other than English exist, or exactly how I realized it. Most people probably first realize that other languages mean other words. It might not be until one actually studies a foreign language that one realizes that the rules of another language can be, and almost certainly are, different from the rules of your mother tongue. Much of what is interesting in languages and in calendars is how those rules differ. A different New Year is a fine time to think about those rules.
Rules
At least from a purely technical point of view, the day on which the year begins is arbitrary. A calendar can use any day as the first day of the year. In the Gregorian Calendar, the next year begins 365 or 366 days after the previous year, with that extra day being added to keep the calendar and the sun aligned. Of course there are other ways of deciding when a new year begins.
What if the solar year isn’t divided into roughly equal twelfths? What if the months are defined by the moon? The moon goes through its phases in a bit less than a twelfth of a solar year. Twelve lunar months is less than a solar year but thirteen is longer than the solar year. One could simply say that the year is twelve lunar months long and start the next year at the start of the next lunar month. One could also be a bit fancier and add a thirteenth month often enough to keep the calendar roughly aligned with the solar year, which is what the Jewish Calendar does.
Different calendars have different rules for how to adjust the year, if they bother to adjust it at all. How much does one adjust with a single adjustment? By a day? By a month? A mixture of the two? How often does one make that adjustment? Every few years according to some rule? Does one use special rules to avoid problematic adjustments? When during the year does one make those adjustments?
The Jewish Calendar adds an extra month every few years on a 19 year cycle. When does it do that? The simple answer is that the extra month is the twelfth month, but it is the twelfth month counting from the ecclesiastical new year, which occurs in the spring, not the civil new year which occurs around the autumnal equinox. Two different beginnings for the year in the same calendar might sound odd to many today, but a few hundred years ago in the English speaking world, the year began both on the first of January and on the 25th of March, depending on how one reckoned. That is the second problem with my first sentence. To be technically correct, I should have stated which new year I meant.
One might assume that adding an extra month would mean that there was no need to have a month like February, which has an adjustable length, but calendars are amazing things, and the Jewish Calendar has two months with adjustable lengths in order to prevent certain holidays (including Rosh Hashanah, civil new year itself) from falling on inappropriate days of the week. To try to put that into terms that might be more familiar to many people (myself included), it would be what would have to be done if Easter was defined not just to be on a Sunday, but on a specific date. The calendar would need to be adjusted by a few days in most years in order to force that date to be on a Sunday.
I sincerely hope that I got this correct. If I missed something, it only goes to show that in researching our genealogy, we can’t take the workings of the calendar in use for granted, and that mistakes are all to easy to make. Our calendar rules are what they are, we just can’t assume that the rules are simple or that our ancestors’ calendars followed the same rules as ours.