Wikipedia:Reference desk/Archives/Humanities/2022 February 8
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February 8
editFrom Passover to Rosh Hashanah is always set at 163 days?
editHi. From Passover to Rosh Hashanah is always set at 163 days. Is there a certain year/date that went into effect? I absolutely cannot find it. — Preceding unsigned comment added by 2600:8806:A300:5200:D1E8:2A15:C1F4:7974 (talk) 17:57, 8 February 2022 (UTC)
- It's a very complicated and detail mathematical calculation. However, the Hebrew calendar is now set, and not fluid. For more information, see Hebrew_calendar#The_fixing_of_the_calendar. Sir Joseph (talk) 21:18, 8 February 2022 (UTC)
- According to that section, "the calendar rules reached their current form by the beginning of the 9th century". Since Adar I, when intercalated, is not inserted between Passover and Rosh Hashanah, and each month between these feasts has a fixed (non-variable) number of days, the interval is fixed by the dates of 14 Nisan for Passover and 1 Tishrei for Rosh Hashanah. --Lambiam 22:01, 8 February 2022 (UTC)
- Passover starts 14 days after Nisan so the perfect fixed interval for this era would be 14 less than ((mean time between current mean Nisan 1.0 or first moonsighting of spring, and the moonsighting 6 lunations later), rounded to the nearest integer). Estimatable by the fraction of a lap the Sun gains on the first point of Aries in these slightly shorter than average 6 lunar months, plus 6, then multiplied by the average size of a tropical month. 27.321582*(6+170.7/360ths)-14=162.88 days. Holy crap! But wait, there's more. The ecliptic is almost vertical in Jerusalem in early spring but diagonal in fall which would make the average exceed 162.88, but not by as much as the 6, 8 hours or so it'd take for distance from the Sun degrees to fully equal degrees lost to slant cause raw degrees from Sol helps difficult moonsightings even if air and light conditions and degrees above horizon are equal. So 163 is still very good for this era even though the Jewish calendar rules presumably tried to fit the slightly different astronomic cycle lengths of many centuries ago. Sagittarian Milky Way (talk) 04:08, 9 February 2022 (UTC)
- The average time from new moon to new in the Jewish calendar is 29 1/2 days plus 44m 3 1/3s. The astronomical value of the excess seconds is 02.87. So alternating months of 29 and 30 days is as good as you're going to get. Our "shadow" Jewish calendar used to fix the date of Easter (in which the "paschal full moon" falls on the fourteenth day of the month Miri) uses the same system. Thus from the Paschal Full Moon (which falls on the fourteenth day of the month) to the first day of the ninth month (Miri is the third month) is (29.5 x 6) = 177 - 13 = 164 days. That agrees with the Jewish calendar because the Passover is the fifteenth day of the month. 2A00:23C5:C712:3801:B08B:106B:82A3:72E6 (talk) 18:44, 12 February 2022 (UTC)
- I should've said 14.00 days to be clear, I haven't been religious in so long I forgot the old-fashioned way some faiths that didn't have zero like to count (music too, octaves, fourths and fifths etc) Sagittarian Milky Way (talk) 23:58, 12 February 2022 (UTC)
- The average time from new moon to new in the Jewish calendar is 29 1/2 days plus 44m 3 1/3s. The astronomical value of the excess seconds is 02.87. So alternating months of 29 and 30 days is as good as you're going to get. Our "shadow" Jewish calendar used to fix the date of Easter (in which the "paschal full moon" falls on the fourteenth day of the month Miri) uses the same system. Thus from the Paschal Full Moon (which falls on the fourteenth day of the month) to the first day of the ninth month (Miri is the third month) is (29.5 x 6) = 177 - 13 = 164 days. That agrees with the Jewish calendar because the Passover is the fifteenth day of the month. 2A00:23C5:C712:3801:B08B:106B:82A3:72E6 (talk) 18:44, 12 February 2022 (UTC)
- Passover starts 14 days after Nisan so the perfect fixed interval for this era would be 14 less than ((mean time between current mean Nisan 1.0 or first moonsighting of spring, and the moonsighting 6 lunations later), rounded to the nearest integer). Estimatable by the fraction of a lap the Sun gains on the first point of Aries in these slightly shorter than average 6 lunar months, plus 6, then multiplied by the average size of a tropical month. 27.321582*(6+170.7/360ths)-14=162.88 days. Holy crap! But wait, there's more. The ecliptic is almost vertical in Jerusalem in early spring but diagonal in fall which would make the average exceed 162.88, but not by as much as the 6, 8 hours or so it'd take for distance from the Sun degrees to fully equal degrees lost to slant cause raw degrees from Sol helps difficult moonsightings even if air and light conditions and degrees above horizon are equal. So 163 is still very good for this era even though the Jewish calendar rules presumably tried to fit the slightly different astronomic cycle lengths of many centuries ago. Sagittarian Milky Way (talk) 04:08, 9 February 2022 (UTC)
- According to that section, "the calendar rules reached their current form by the beginning of the 9th century". Since Adar I, when intercalated, is not inserted between Passover and Rosh Hashanah, and each month between these feasts has a fixed (non-variable) number of days, the interval is fixed by the dates of 14 Nisan for Passover and 1 Tishrei for Rosh Hashanah. --Lambiam 22:01, 8 February 2022 (UTC)