The Jewish Calendar - Implications for Jewish ritual
"When the 19-year intercalary cycle was finalised in the 4th century, the earliest Passover (in year 16 of the cycle) coincided with the northward equinox, which means that Passover fell near the first full moon after the northward equinox, or that the northward equinox landed within one lunation before 16 days after the molad of Nisan. This is still the case in about 80% of years, but in about 20% of years Passover is a month late by these criteria (as it was in AM 5765 and 5768, the 8th and 11th years of the 19-year cycle = Gregorian 2005 and 2008 CE). Presently this occurs after the "premature" insertion of a leap month in years 8, 11, and 19 of each 19-year cycle, which causes the northward equinox to land on exceptionally early Hebrew dates in such years. This problem will get worse over time, and so beginning in AM 5817 (2057 CE), year 3 of each 19-year cycle will also be a month late. If the calendar is not amended then Passover will start to land on or after the summer solstice around AM 16652 (12892 CE). (The exact year when this will begin to occur depends on uncertainties in the future tidal slowing of the Earth rotation rate, and on the accuracy of predictions of precession and Earth axial tilt.)
The seriousness of the spring equinox drift is widely discounted on the grounds that Passover will remain in the spring season for many millennia, and the text of the Torah is generally not interpreted as having specified tight calendrical limits. Of course, the Hebrew calendar also drifts with respect to the autumn equinox, and at least part of the harvest festival of Sukkot is already more than a month after the equinox in years 1, 9, and 12 of each 19-year cycle; beginning in AM 5818 (2057 CE), this will also be the case in year 4. (These are the same year numbers as were mentioned for the spring season in the previous paragraph, except that they get incremented at Rosh Hashanah.) This progressively increases the probability that Sukkot will be cold and wet, making it uncomfortable or impractical to dwell in the traditional succah during Sukkot. The first winter seasonal prayer for rain is not recited until Shemini Atzeret, after the end of Sukkot, yet it is becoming increasingly likely that the rainy season in Israel will start before the end of Sukkot.
No equinox or solstice will ever be more than a day or so away from its mean date according to the solar calendar, while nineteen Jewish years average 6939d 16h 33m 031⁄3s compared to the 6939d 14h 26m 15s of nineteen mean tropical years. This discrepancy has mounted up to six days, which is why the earliest Passover currently falls on 26 March (as in AM 5773 / 2013 CE)."
This year, 2016, is one example of the 20% of the time mentioned above, as the Jewish Passover fell 18 days after the appropriate time this year. This may not seem significant to some, but for those who feel that the cycles should be kept as consistently as possible, this is for you.
""About the time of the end, a body of men will be raised up who will turn their attention to the Prophecies, and insist upon their literal interpretation, in the midst of much clamor and opposition."
Sir Issac Newton 1642-1727
Anaviel Ben Eleazer HaCohen April 28, 2016