[whatwg] Fwd: <time>

[Aryeh Gregor]

On Sun, Mar 15, 2009 at 6:30 PM, Tom Duhamel <tom420.duhamel at gmail.com> wrote:
> What about those 'other calendars of concern'? Are they reasonably
> compatible with Gregorian, or so much different that my example of the Mayan
> long count becomes a good one? I know nothing about those, but I fear it's
> the later.

You're correct.  For instance, the Jewish calendar has 12 months of 29
or 30 days, except that sometimes it has 13 months, and it only syncs
up with the Julian calendar every 19 years, except sometimes when it's
off by a day, and the algorithm for calculating whether months have 29
or 30 days depends on when the new moon will hypothetically first be
visible in Jerusalem according to an astronomical model that was
finalized early in the first millennium CE, plus also on when certain
holidays would fall out in the coming year.

I don't know much about the other calendars, but they're similarly
unrelated to the Gregorian calendar, for sure.  Apparently, some
variants of the Islamic calendar aren't even planned out in advance --
you literally have no idea whether the current month is going to be 29
days or 30 until it's actually announced based on observation of the
new moon, and different Muslim countries decide it differently.  There
are variants that allow the start of Islamic months to be calculated
in advance, but there seem to be several different ones.