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Tekufas Tishri, autumnal equinox
Tekufas Nisan, vernal equinox
Tekufas Tevet, winter solstice
Tekufas Tammuz, summer solstice
Once a permanent calendar was introduced, the need for independently computing the beginning dates of these seasons no longer existed. These dates are listed in Jewish calendars, however, because two prayers of the Jewish ritual are determined by the Tekufoth, and not by fixed dates:
The Sheelah, a prayer for rain, which is recited from the 60th day in Tekufas Tishri until Pesach.
Kiddush Hahammah, a blessing of the sun, which is recited on Tekufas Nisan every 28th year. The 28-year cycle, called the Mahzor Gadol or Great Cycle, is based upon a calculation which places the sun in the same position as it was on the day of Creation every 28 years.
The basis for the dating of these prayers is a series of calculations from the third century by Talmudic scholar Samuel Yarhinai. The ''Tekufoth according to Samuel" is based upon the Julian year length of 365 days and 6 hours. Samuel simply divided this figure by four to obtain a period of 91 days and 7.5 hours for each season. The date of the first Tekufas Nisan was then calculated (Tuesday at 6.p.m., Anno Mundi 1 Adar 22), and from this beginning point, all successive Tekufoth were calculated.
Another calculation method, attributed to Rabbi Adda, is based upon a figure of 365 days, 5 hours, 997 halakim, and 48 regaim, which is both more accurate and more consistent with the Jewish calendar itself but has not been accepted. Thus, the dates of
Table 9.18 Kebioth for leap years.
Year TypeFirst Day of Rosh HashanahYear LengthYear TypeFirst Day of Pesach
8Monday383defectiveThursday
9Thursday383defectiveSunday
10Sabbath383defectiveTuesday
11Tuesday384regularSabbath
12Monday385excessiveSabbath
13Thursday385excessiveTuesday
14Sabbath385excessiveThursday

 
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