calendars

[cellio]

Idle question the first: what is the origin of Shabbat (or Yom Tov) beginning 18 minutes before sunset? That is, the idea of starting early is solidly talmudic, but what is the significance of 18 minutes in particular? It is worth noting, as well, that many time differentials are in proportional hours (a day always has 12 hours; sometimes they're longer and sometimes they're shorter), but "18 minutes" is a constant. (Online search in the Soncino talmud isn't doing it for me, though I may be doing something wrong in specifying the search, given the lack of documentation.)

Idle question the second: the issues of Shabbat (etc) times for astronauts (e.g. on the shuttle or space station) are well-understood, but what will we do when we colonize other planets? If you don't go with the local times, things get rapidly wonky, with Shabbat perhaps starting mid-day one week and at dawn the next and so on. If you do go with local times, then you quickly have calendar drift with respect to Earth -- and you may need to change the number or length of months, if you want a physical year to equal a liturgical year. If you don't do that, your holidays move around all over the place like on the Muslim calendar.

Comments

[aliza250.livejournal.com]

I was just in Australia. South of the equator, the seasons are flipped, and the first Jews in Oz had a discussion about how that would affect things - not so much the idea of, for example, celebrating Pesach in the fall, but little things like when to pray for dew vs. rain (tal vs. geshem.)

The answer was, there as everywhere else, was to follow Eretz Yisrael. Thus, I'd assume that Martian Jews would follow the holiday dates of Earth, and let the seasons float around the calendar.

There are bigger issues with *day* length - for example, how do you count the Omer if you miss one day out of every 25? (Mars days are slightly longer than Earth days, but not so much longer that people don't think our bodies could adapt to local daylight hours.)

[cellio]

The answer was, there as everywhere else, was to follow Eretz Yisrael. Thus, I'd assume that Martian Jews would follow the holiday dates of Earth, and let the seasons float around the calendar.

It's a tough call. Things may be flipped in Oz but a year there equals a year in Jerusalem, so at least it's consistent. On Mars, you'd be moving around through the year And to stay in sync you'd also have to have 24-hour days, and that could get weird. We have a strong tradition of heeding local sunrise/sunset times, but of course that assumes 24-hour days...

(And then there's the question of blessing the new moon each month when you can't even see it from Mars. :-) )