The perpetual calendar
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From: Yusuf B Gursey on 19 Feb 2010 10:56 On Feb 19, 5:14 am, Ruud Harmsen <r...(a)rudhar.eu> wrote: > Fri, 19 Feb 2010 10:34:10 +0100: James Hogg <Jas.H...(a)gOUTmail.com>: > in sci.lang: > > >What could be simpler? > > The Jewish calendar. the Jewish Calendar has a complicated algorithm, IIRC refined by the famous 18th cent. mathematician Euler. the complications are due to making sure that certain holidays do not fall on certain days. http://en.wikipedia.org/wiki/Hebrew_Calendar << Hebrew calendar .... Special holiday rules Adjustments are made to ensure certain holy days and festivals do or do not fall on certain days of the week. Yom Kippur Adjustments are made to ensure that Yom Kippur, on which no work can be done, does not fall on Friday (the day prior to the Sabbath) to avoid having Yom Kippur's restrictions still going on at the start of Sabbath, or on Sunday (the day after Shabbat) to avoid having the Shabbat restrictions still going on at the start of Yom Kippur. The Rosh Hashanah postponement rules are the mechanism used to make the adjustments. As Yom Kippur falls on Tishrei 10, and Rosh Hashanah falls on the 1st, the adjustment is made so that Rosh Hashanah does not fall on a Wednesday or Friday. To ensure that Yom Kippur does not directly precede or follow Shabbat, and that Hoshana Rabbah is not on a Shabbat, in which case certain ceremonies would be lost for a year, the first day of Rosh Hashanah may only occur on Mondays, Tuesdays, Thursdays, and Saturdays (the "four gates"). Adjustments are made to ensure that Rosh Hashanah does not fall on the other three days. To achieve that result the year may be made into a short (chaser) year (both Kislev and Cheshvan have 29 days) or full (maleh) year (both Kislev and Cheshvan have 30 days). (see table) The day of the week on which Rosh Hashanah falls in any given year will also be the day on which Sukkot and Shmini Atzeret will occur. >> > > -- > Ruud Harmsen,http://rudhar.com >>
From: António Marques on 19 Feb 2010 10:59 Yusuf B Gursey wrote (19-02-2010 15:35): > the Orthodox (Eastern) churches have a slightly different system. > dunno exactly what it is. Afaik the system is the same, it's March 21 that is different.
From: Mike Barnes on 19 Feb 2010 11:25 John Atkinson <johnacko(a)bigpond.com>: >Halmyre wrote: >> >> I just wish they'd settle on a date for Easter and be done with it. >> >But, the whole point of Easter is that it has a full moon! A full-*ish* moon, actually. The definitions of the equinox and full moon used when determining Easter are rather different from the real definitions used by astronomers, which would actually give rise to different (perhaps several weeks different) Easter dates depending on one's longitude. But I thought that for most people the whole point of Easter is that they get time off work. -- Mike Barnes Cheshire, England
From: Evan Kirshenbaum on 19 Feb 2010 11:52 "Peter T. Daniels" <grammatim(a)verizon.net> writes: > On Feb 19, 4:34�am, James Hogg <Jas.H...(a)gOUTmail.com> wrote: >> My Book of Common Prayer makes things easy by pointing out that >> "the moon referred to in the definition of Easter Day is not the >> actual moon of the heavens, but the Calendar Moon, or Moon of the >> Lunar Cycle, which is counted as full on its fourteenth day, >> reckoned from the day of the Calendar New Moon inclusive." Also, in >> a Bissextile Year "the number of Sundays after Epiphany will be the >> same, as if Easter Day had fallen one day later than it really >> does." > > Which is why Easter and Passover rarely coincide -- we happen to have > had a spate of coincidence in recent years, but that'll soon be over. Which years were those? I had thought that the current Easter rules made it impossible for it to fall on the 15th of Nissan. -- Evan Kirshenbaum +------------------------------------ HP Laboratories |We never met anyone who believed in 1501 Page Mill Road, 1U, MS 1141 |fortune cookies. That's astounding. Palo Alto, CA 94304 |Belief in the precognitive powers |of an Asian pastry is really no kirshenbaum(a)hpl.hp.com |wackier than belief in ESP, (650)857-7572 |subluxation, or astrology, but you |just don't hear anyone preaching http://www.kirshenbaum.net/ |Scientific Cookie-ism. | Penn and Teller
From: LFS on 19 Feb 2010 12:02
Evan Kirshenbaum wrote: > "Peter T. Daniels" <grammatim(a)verizon.net> writes: > >> On Feb 19, 4:34 am, James Hogg <Jas.H...(a)gOUTmail.com> wrote: > >>> My Book of Common Prayer makes things easy by pointing out that >>> "the moon referred to in the definition of Easter Day is not the >>> actual moon of the heavens, but the Calendar Moon, or Moon of the >>> Lunar Cycle, which is counted as full on its fourteenth day, >>> reckoned from the day of the Calendar New Moon inclusive." Also, in >>> a Bissextile Year "the number of Sundays after Epiphany will be the >>> same, as if Easter Day had fallen one day later than it really >>> does." >> Which is why Easter and Passover rarely coincide -- we happen to have >> had a spate of coincidence in recent years, but that'll soon be over. > > Which years were those? I had thought that the current Easter rules > made it impossible for it to fall on the 15th of Nissan. > I understood that it is not actually impossible but that the coincidence is very rare. ISTR it happened at some point in the early 1980s. Of course, Passover week quite often covers Good Friday and Easter Sunday - it does this year. -- Laura (emulate St. George for email) |