Trutharchivist

So, as you can see, today is my birthday according to the Christian Calendar, but not according to the Hebrew one. So, I decided to take this as a chance to explain at length about the difference between those two calendars. It's going to be a somewhat long rant, so you may prefer to skip it and just congratulate me for my birthday. You may well do so. Some others may already know everything I'm about to write here. You may skip it too - not that any of you needed permission for that.

Anyway, I'll start at the very beginning. What humans started measuring time in a large scale, they needed a big unit of time - what we now call a year. They built it to align with natural circles, which revolved around seasons. Those seasons meant a lot for crops - you had to plant in one season, and you had to take care of the crops until you harvest it. This circle was based on the Earth's circumference around the sun, though they didn't know that. But after having the year as a unit, they needed (for some reason) to divide it to smaller parts. The way they did this was by watching the moon waxing and waning, creating the month (which, of course, derives from moon). The problem was that in one solar year there is just a little over twelve months - about ten and a half more days. And that's where different calendars start. I have no idea how, say, the Aztec calendar or the Chinese one works. I do know a thing or two about the Muslim, Jewish and Christian calendars, so I'll talk about them.

As I understand it, the ancient Romans just saw that there were roughly twelve months a year, and gave up on aligning with the moon - changing the length of months to vary from 29 to 31 (the 28 days month was a little late change, though it was still during the Roman empire days). Since the solar year is still quarter a day longer than what they've got - because no one wants a day to be partially in one year, partially in another - they added a day to the year once each four years. As most of you know, Pope Gregory XIII changed a few things with that, and after a few more fixes the leap days occur a little differently nowadays, though it's still generally once each ten years. The reason that those fixes were needed was - surprise, surprise - because the length of a solar year is a little less than 365.25 days.

Now, let's get to the Muslim calendar. I admit that I don't know much about it, but for some reason, the Arabs gave up on the solar calendar - perhaps because generally they weren't farmers; on the desert, it's somewhat easier to be a shepherd. So they had their year built around twelve lunar months. They start each month when the moon starts waxing, and end it when it finished waning. They (I think) have calculations on which day it's supposed to happen, and they have people watching for it (again, I think). Because of that, their whole year shifts in seasons regularly. I'm sure that they're glad when the Ramadan occurs this time of the year, when the days are shorter and the nights are longer.

And now, for the Jewish calendar. In my opinion it's more complicated than both calendars, but you may judge for yourself. It works with twelve lunar months, but since according to the bible Passover has to be during the spring, it also tries to align with the solar year. Now, since the solar year is almost eleven days more than twelve lunar months, to stay aligned with the solar year the Jewish calendar has every three years or so an additional month - this very year (well, the Jewish year) we have one. Though, to actually have the two kinds of years aligned completely, the Jewish calendar works in nineteen years cycles, since nineteen solar years equals almost exactly to 235 lunar months, which is nineteen times a lunar year with seven of them getting an additional month. About two thousand of years ago (actually a little less, more about 1700 or so, but I'm not completely sure about that), after years of having the judges of the main court in Israel decide on when months started based on testimonies about the renewal of the moon, and on when to add months according to some variables, there was a Jewish sage that calculated the years to come and built the Jewish calendar as we know it today. The reason he had for doing so was that the learning centers in Israel were dwindling at the time, and just a couple of generations afterwards there weren't Jewish sages in Israel anymore. A couple of centuries later, one of if not the most important Jewish Rabbis, Maimonides (aka Rambam or Rabbi Moshe Ben Maimon) wrote down in a book all the calculations of the length of a lunar month, a solar year, the differences between them and basically how to calculate when the next renewal of the moon is supposed to be. I'm not sure how much it changed the Jewish calendar, but it's sometimes fun to use it, if you have the willpower to learn it all. Seriously, it's very complicated. Besides the fact that it's not completely accurate, since it's based on a Geocentric model of the universe.

This is why the last time my Jewish calendar birthday and my Christian Calendar one aligned was two years ago - when I was nineteen - right before I joined the Shard. And that is why there are still a couple of years before it'll happen again. Though next year my Christian Calendar birthday (CCB, because acronyms) will occur before my Jewish calendar one (JCB, because... You know), so your greetings will come early!

Thank you for reading, and have a good night/day/afternoon/evening/whatever portion of the day you're at when reading this!