So why does chanukah start in November this year? does it change every year? And what’s the criteria for its change? Sorry for all the questions, Google was NOT helpful DX
Hi! It's cause the Jewish calendar is different from the Gregorian calendar. Chanukah is on the 25th of the Jewish month of Kislev every year, but Jewish calendar dates don't correspond to fixed dates on the Gregorian calendar, because the two calendars are not in sync with one another.
The Gregorian calendar is a solar calendar, which means it is aligned to the solar year, which is the amount of time it takes the Earth to revolve around the sun. Some calendars, like the Islamic calendar, are lunar, which means they are aligned to the cycles of the moon. The Jewish calendar is lunisolar, which means it's lunar but it has some adjustments to keep it in line with the solar year.
To break that down a little -- there are about 12 moon cycles in a solar year, but not exactly 12. The Gregorian calendar deals with this by having slightly longer months than moon cycles, so around 30 or 31 days when a moon cycle is 29.5 days. And the beginnings of the month are not aligned with new moons. Then, it makes some slight adjustments like leap years to keep things even more consistent.
The Islamic calendar, on the other hand, is almost purely lunar. It's comprised of 12 months, each of which start around the new moon. What that means is that the Islamic calendar year is slightly shorter than a solar/Gregorian year. The Islamic year is 354 or 355 days, as compared to the Gregorian year which is 365. The result of this is that Muslim holidays move "backwards" from one year to the next -- a year and a half ago Ramadan started on April 24, this past year on April 13, and this coming year it will start on April 3. This means that the Islamic calendar is not fixed to seasons; Ramadan will move all the way around the year and eventually come back to April.
The Jewish calendar is also lunar, and also utilizes 12 months beginning around the new moon, and also has 353/354/355 days, so you'd expect the same thing to happen. Except! Ancient Jewish civilization was agricultural. As such, it wanted its calendar and holidays to align to the seasonal, agricultural cycle. So, what it does to align itself to the solar year is to add an entire extra month every few years. So, most Jewish years are around 354 days, but some Jewish years are 384 days. Remember, the goal is to get the average to be around 365.
The result of this is that, like the Islamic calendar, holidays move around from year to year because the difference in length between the lunar year (12 lunar months) and the solar year (365 days). Then every so often we add an extra month (it's an extra Adar, around February/March) and that suddenly shifts everything later, before it drifts backward again.
So, this year all the holidays were very early. Not only is Chanukah in November, but all the fall holidays were in September (usually at least one if not more are in October), Passover started in March (it's usually in April), etc. This coming winter, as you can probably guess, we will be having an extra month to realign things again. So next year, Chanukah will be in late December!
Fun fact: The extra month is actually a very slight overcorrection and because of this, the entire Jewish calendar is actually drifting very slightly forward. That means that 2013 was the second-to-last Thanksgivukkah ever (with the last one coming up in 2070) — at least until the calendar loops all the way back around in 70,000 years. Hopefully we decide to introduce a new correction before that happens, though!
tl;dr: The Jewish calendar is different from the Gregorian calendar. It's a combination of lunar and solar, whereas the Gregorian is just solar.
