Editing Hebrew calendar (section)

====Cycles of years====
Since the Jewish calendar has been fixed, leap months have been added according to the [[Metonic cycle]] of 19 years, of which 12 are common (non-leap) years of 12 months, and 7 are leap years of 13 months. This 19-year cycle is known in Hebrew as the ''Machzor Katan'' ("small cycle").

Because the Julian years are {{frac|365|1|4}} days long, every 28 years the weekday pattern repeats. This is called the sun cycle, or the ''Machzor Gadol'' ("great cycle") in Hebrew. The beginning of this cycle is arbitrary. Its main use is for determining the time of [[Birkat Hachama]].

Because every 50 years is a Jubilee year, there is a jubilee (''yovel'') cycle. Because every seven years is a sabbatical year, there is a seven-year release cycle. The placement of these cycles is debated. Historically, there is enough evidence to fix the sabbatical years in the [[Second Temple Period]].<ref>B. Zuckermann, ''A Treatise on the Sabbatical Cycle and the Jubilee'', trans. A.&nbsp;Löwy. New York: Hermon Press, 1974.</ref> But it may not match with the sabbatical cycle derived from the biblical period; and there is no consensus on whether or not the Jubilee year is the fiftieth year or the latter half of the forty ninth year.

Every 247 years, or 13 cycles of 19 years, form a period known as an ''iggul'', or the ''Iggul of [[Nahshon ben Zadok|Rabbi Nahshon]]''. This period is notable in that the precise details of the calendar almost always (but not always) repeat over this period. This occurs because the ''molad'' interval (the average length of a Hebrew month) is 29.530594 days, which over 247 years results in a total of 90215.965 days. This is almost exactly 90216 days – a whole number and multiple of 7 (equalling the days of the week). So over 247 years, not only does the 19-year leap year cycle repeat itself, but the days of the week (and thus the days of Rosh Hashanah and the year length) typically repeat themselves.<ref>Nadia Vidro, "The Origins of the 247-Year Calendar Cycle", ''Aleph'', '''17''' (2017), 95–137 [https://doi.org/10.2979/aleph.17.1.0095 doi link].</ref><ref>Dov Fischer, [https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4364371 The Enduring Usefulness of the Tur’s 247-year Calendar Cycle (Iggul of Rabbi Nachshon)]</ref>