Sources and reasoning:
The duration of bein ha-shemashot
The Gemara in Shabbat 34b explains that the duration of bein ha-shemashot is the time it takes to walk three-quarters of a mil after sunset, and after this period comes tzeit ha-kochavim. The Shulchan Aruch likewise rules in practice, Orach Chayim 261:2, that the duration of bein ha-shemashot is the time it takes to walk three-quarters of a mil, namely, 1,500 amot.
Regarding the duration of walking a mil, there are three views among the Rishonim: whether walking a mil takes 18 minutes, 22.5 minutes, or 24 minutes. Halachically, we rule that walking a mil takes 18 minutes; therefore, the duration of bein ha-shemashot, which is three-quarters of a mil, is 13.5 minutes. This is explained by the Mishnah Berurah there, Orach Chayim 261, and this is also the halachic ruling of Maran Rabbi Ovadia Yosef.
Although the Gemara gives a fixed measure of time that does not depend at all on degrees or seasonal minutes, but rather a fixed period of 13.5 minutes, this time measure was stated with reference to the horizon of Eretz Yisrael and Babylonia during Nisan and Tishrei, when day and night are equal. However, in winter or summer, and likewise in places distant from the equator, the times differ, and bein ha-shemashot becomes shorter or longer accordingly.
As the poskim have ruled, see the Biur Halachah and Mishnah Berurah, סימן רסא, note 23, where he emphasizes this point. This is the language of the Mishnah Berurah there:
Regarding Motzaei Shabbat, see the Biur Halachah, where we explained in the name of the poskim that, according to all views, the measure of three-quarters of a mil changes according to the time and place. This was stated in the Gemara only with respect to the horizon of Babylonia and during Nisan and Tishrei, when day and night are equal. In our regions, which are inclined toward the north of the world, it becomes much longer. Therefore, one must be very careful not to perform labor on Motzaei Shabbat, even after much time has passed since sunset, until three small stars are visible, as set forth below in סימן רצ”ג, section 2; see there in the Mishnah Berurah and Biur Halachah.
שו”ת Yabia Omer, vol. II, Orach Chayim, siman 21, likewise writes concerning the time of Rabbeinu Tam:
In my humble opinion, it appears that he holds as the Minchat Kohen wrote (Maamar 2, ch. 3 and onward): that the measure of four mil stated by the Sages is in seasonal hours, not standard hours. Consequently, during the summer (or even during Nisan and Tishrei, according to the current practice of calculating from alot ha-shachar until tzeit ha-kochavim), the time will reach an hour and a half, and sometimes more. Although the Pri Megadim (siman 261) holds that four mil should be calculated in standard hours, the Mishnah Berurah already wrote in the Biur Halachah there, s.v. “shehu,” that the words of the Magen Avraham in the name of the Mahari”l imply the view of the Minchat Kohen, and that this is also the view of the Vilna Gaon there. See there. See also שו”ת Rav Pe’alim, vol. II, siman 19. This requires further study. See there.
The correct calculation is according to “degrees”
Since, as stated, the duration of bein ha-shemashot applies only in Eretz Yisrael or Babylonia during Nisan and Tishrei, we must know how to calculate the duration of bein ha-shemashot in other countries and at other times of the year.
For this purpose, the poskim wrote that one should take the degree position at which the sun is below or above the horizon during Nisan and Tishrei in Eretz Yisrael or Babylonia, and determine the period in which the sun reaches those degrees during other times of the year or in other countries.
For example, one takes the measure of 72 minutes for alot ha-shachar on an equinoctial day during Nisan or Tishrei and calculates how many degrees the sun is below the horizon at that time. Whenever the sun reaches those degrees throughout the year, we know that it is then alot ha-shachar, even if the time period extends to an hour and a half or more.
Why can this not be calculated according to seasonal minutes? Because there is no connection between the length of the day and the position of the sun. For example, specifically during the short winter days, when seasonal hours are shorter, bein ha-shemashot—and likewise alot ha-shachar—actually becomes longer, because the time for the degrees is longer. This was likewise written as halachah by HaGaon Rabbi Meir Mazuz shlit”a in an article in the journal “Or Torah” [Tevet 5755, siman 41].
It should be explained that although the poskim did not mention calculating by degrees, but spoke only of calculating seasonal hours, and likewise the Ohr HaChayim calendar, upon which Maran Rabbi Ovadia Yosef zt”l relied, does not calculate according to degrees but according to seasonal minutes, the reason is that in Eretz Yisrael there is not a very great difference between calculation by degrees and calculation by seasonal minutes. Therefore, they never needed a calculation by degrees and customarily calculated according to seasonal minutes. In Europe, however, one must adhere to the correct calculation, namely by degrees, because the discrepancy between seasonal minutes and the actual time of sunset and tzeit ha-kochavim according to the visible signs of light and darkness is very great.
Regarding the times for the conclusion of Shabbat and the end of the Yom Kippur fast, since, as explained in the Shulchan Aruch, Orach Chayim 293, the measure is not determined by the end of bein ha-shemashot but by the visibility of three medium-sized stars in the sky, most poskim estimate this time as between 32 minutes in winter and 38 minutes in summer, averaging 35 minutes.
Since this time is, according to the degrees method, when the sun is 8 degrees below the horizon, this time is likewise determined in Europe and similar locations when the sun is 8 degrees below the horizon. Therefore, the conclusion of Shabbat is often greatly delayed—up to an hour or more after sunset—because it takes a long time in European countries for the sun to reach the position of eight degrees below the horizon.
The Mishnah Berurah already addressed this in his Biur Halachah to siman 293, writing that in Europe the conclusion of Shabbat is very late, for the reason explained above.
This response was translated automatically from Hebrew and has not yet been reviewed by a person. Therefore, it may contain inaccuracies and should not be considered a definitive reference.
