There is a Babylonian luni-solar calendar used by Jews, as mentioned above, which determines the dates of public holidays in Israel, but (correct me if I am wrong!) it is not generally used for civil purposes and people do not “follow” it.
I stand corrected. DPRK is correct. Here is what Dr. Google has to say:
Israel uses both the Gregorian calendar (for civil/international purposes) and the Hebrew calendar (for Jewish religious observance and as an official national calendar for holidays like Independence Day). While the Gregorian is used for daily business, schools, and finance, the Hebrew calendar determines Jewish holidays, dates, and is often seen alongside Gregorian dates on official documents, connecting the nation to its religious and historical heritage.
I usually don’t know the Hebrew date off the top of my head, but I can usually calculate it pretty quickly by remembering when the last holiday was and counting forward from there.
Christians do too, but only for one holiday: Easter is based on the Jewish lunar calendar, and so moves around each year. But it has been re-defined to be calculable in the Gregorian system.
Today is January 3, 2569 in Thailand for almost all purposes (including Google results despite preference cookies); but most Thais are aware of the alternate year designation, 2026. If these are considered different calendars then Thailand uses vestiges of FIVE different calendars! There are three different days (January 1, April 13, and a moving feast typically in February) where “Happy New Year” is heard as a greeting. A 4th (moving, full moon) holiday in November isn’t called “New Year”, but is the culmination of an ancient lunar calendar distinct from the Chinese calendar.
Does get a little tricky to answer “what’s today’s date?” in Thailand, apparently. Are they the most complex culture around on that subject?
True enough. But …
If you ask any Xian “What date is Easter 2026?” the answer they give will be the Gregorian one. Which they had to Google or consult some other professional calendar source to discover. (April 5th 2026).
Damned few (read “effectively zero”) Xians know how to, much less will, compute the date of Easter from first principles in any calendar, Gregorian or otherwise.
Whereas i, a secular Jew who mostly uses the Gregorian calendar, will sometimes look at the moon and think, “we must be close to Rosh Hashanah.”
I’m a secular secularist who knows no calendar other than Gregorian. I certainly know of many other calendars, but close to nothing beyond the fact of their existence.
OTOH, I follow the progression of the Moon and can generally tell you what the current phase is and rough times of moonrise & set. I try to look at the Moon every day it’s visible. Which is most of them if you’re diligent about it. It just takes a moment to scan the sky. To me it feels like a way to remain grounded a teeny bit in Nature despite living in a nearly totally artificial environment.
BTW, IIRC the Jewish calendar does not depend on actual, naked-eye sighting of the real Moon, though! That is in Islam.
No, after most of the Jews were forced out of Israel, the rabbis came up with a formula that keeps the calendar on track. But the formula works, and you can tell when the month begins by looking at the sky.