Rambam - 3 Chapters a Day · Chabad.org: SIE Rambam

9th Perek: Laws of Kidush Hachodesh

April 6, 2026·39 min·3 clips

Why do Jewish sages disagree on the solar year's length when physical facts should have no debate?

The lesson opens with scope. Chapter 9 has eight halachos on figuring out the weekday and monthly date when the tekufah will land. First comes the split over the solar year. Some sages use 365 days and six hours. Others make it slightly shorter. The host treats that difference with care, and sets it beside similar debates among Greek and Persian sages over the exact solar year. Then the page turns into a workshop. For the first year of a nineteen-year cycle, tekufah Nisan has a starting point. From there, the listener counts. Each tekufah moves ahead by ninety-one days and seven and a half hours, so the calendar comes together one measured interval at a time. Later years take more bookkeeping. Each completed nineteen-year cycle adds one hour and 485 fractional parts. Each completed year in the current cycle adds ten days, twenty-one hours, and 204 fractional parts, the solar year's excess over the lunar year. Then comes the subtraction: seven days, nine hours, and 642 fractional parts. After that, reduce the remainder by lunar months of twenty-nine days, twelve hours, and 793 fractional parts, dropping the whole months as the procedure requires. The sanity check at the end is useful. Usually the adjustment adds one, two, or three days. Four can happen, but barely. Five or six means the math has gone wrong; go back and calculate again, more carefully.

As heard by us

A careful lesson in tekufah and Jewish calendar calculation.

Chapter 9 of Hilchas Kiddush HaChoiddish leans into calendar arithmetic without softening it. It walks through the tekufah of Nissan, the competing estimates of the solar year, the nineteen-year cycle, and the additions and subtractions needed to reach the date.

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Follow the calendar math behind tekufah, Nissan, and the 19-year cycle.

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