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The perpetual calendar
On Feb 19, 5:14*am, Ruud Harmsen wrote:
Fri, 19 Feb 2010 10:34:10 +0100: James Hogg : 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 |
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