Tekufat Shmuel (the Julian year): A Modern Commentary to Maimonides הלכות קידוש החודש Chapter 10

תקציר

<p>תקופת שׁמואל מבוססת על שׁנה שׁל 365.25 יום. למה הקדישׁ רמב"ם פּרק לנושׂא? סיבה אחת: ט"ז ניסן חל פּחות משׁלשׁים יום אחרי תקופת ניסן אפילו בשׁנות עיבור</p>Tekufat Shmuel (though Rambam never calls it by this name) is based on the Julian solar year of 365.25 days. In the span the 19-year cycle, the Julian years accumulate an excess of 0.06 days over Jewish calendar years which average 365.2468 days. The Julian year can be expressed as 365 days and 6 hours, or 364 days and 30 hours. Thus, each of the four seasons is 91 days, 7.5 hours. Tekufat Nisan can occur at 0,6,12,18 hours of the day. Tekufat Nisan, Tamuz, Tishrei, Tevet are each separated from the preceding Tekufah by 7.5 hours. The epoch Tekufat Nisan was at the start of Wednesday; 7 days, 9 hours, 642 parts before Molad Nisan. Likewise, in the first year of each 19-year cycle, Tekufat Nisan precedes the molad by 7:9:642, but there is a progression of 0.06 days every 19 years. Every 28 years, Tekufat Nisan is on Wednesday at zero hours. The weekday and time of Tekufat Nisan is determined by the year number in the 28-year cycle. Once the weekday of Tekufat Nisan is known, Rambam provides an algorithm for determining its date in Nisan (and occasionally in Adar 2). This algorithm provides a tentative minimum date in Nisan, but additional days must usually be added to reach the predetermined weekday of the Tekufah. Rambam indicates that his parameters are valid for the era of 1170 CE. In our era of 2024 CE, two to three additional days need to be added. There are certain features of Rambam's algorithms (eleven days; dropping multiples of 30) which are reminiscent of Easter Computus based on the Julian calendar. <br> <br>