By Rabbi Ahron Notis
Mosaica Press
Beit Shemesh, Israel, 2022
188 pages
Reviewed by Rabbi Yaakov Hoffman
Everyone seems to have an opinion on zemanim, but few truly understand the subject. Rabbi Ahron Notis, a rebbi in Mayan Hatalmud Yeshiva in Lakewood, New Jersey, and a researcher for ArtScroll Publications, has provided an erudite guide to elucidate this topic both in terms of halachah and metzius (scientific reality).
He presents astronomic terms and concepts clearly, explaining and illustrating how the understanding of celestial phenomena has developed from the times of Chazal until the present day. Despite being involved in the subject of zemanim for years, I found that the scientific portion of the book deepened my understanding of the history and terminology.
Rabbi Notis emphasizes the importance of an accurate grasp of scientific reality as a prerequisite to issuing halachic rulings. For example, he rightly notes that calendars and apps must calculate zemanim, such as alos hashachar (dawn) and tzeis hakochavim (nightfall), using solar depression angles (“degrees”). Unlike using a fixed amount of time before sunrise or after sunset, this method approximates observation and accounts for fluctuations in the rate that day breaks and night falls.1 However, the book’s tone when discussing the lack of scientific knowledge of previous generations (and some contemporary rabbis) is unnecessarily harsh. It is also disconcerting that Rabbi Notis presents his halachic rulings as the final word in accurate zemanim; in fact, some of his halachic positions are arguable.
The book’s most significant halachic formulation is an unequivocal calculation for the much-debated zeman of tzeis hakochavim, the appearance of three medium-sized stars, which heralds the onset of night and hence the new halachic day. The Talmud states that bein hashemashos (the transitionary period between day and night) begins when the sun sets; definitive nightfall occurs after the amount of time that it takes to walk three-quarters of a mil (Shabbos 34b). Rabbi Notis is confident that the mil is 22 ½ minutes;2 therefore, nightfall occurs 16 ⅞ minutes after sunset. The Vilna Gaon writes that this refers to Eretz Yisrael at the equinox (Biur HaGra, Orach Chaim 261); at that time, the sun is 4.37 degrees below the horizon, and one can use that figure to extrapolate the time of tzeis for any location and season. By this reckoning, tzeis hakochavim in New York is never later than 23 minutes after sunset, even at the height of summer.
Rabbi Notis’s calculation follows the trend of some contemporary scholars to determine the time for tzeis hakochavim based on its relationship to sunset.3 However, this is a departure from the traditional approach. Before the advent of clocks, calendars and light pollution, Jews determined the time of nightfall first and foremost by visual perception of three stars.4 Tzeis was the central zeman; other zemanim were determined in relation to it, not vice versa.
Before the advent of clocks, calendars and light pollution, Jews determined the time of nightfall first and foremost by visual perception of three stars.
Rabbi Notis acknowledges that it is very difficult to see three stars at -4.37 degrees; it is generally only possible if one has excellent eyesight and knows in advance where to look. While some sources do indicate that a certain amount of skill is required to see the three stars the moment they appear, there is nevertheless no evidence that any Jewish community before the contemporary era ever considered tzeis hakochavim to be as early as -4.37 degrees.5 This was true even in Eretz Yisrael and the surrounding areas, where residents could theoretically have simply waited three-quarters of a mil after sunset at the equinox without recourse to astronomic calculations.
It is also worth noting that the Shulchan Aruch, following earlier authorities, rules that when a Biblical precept is at stake, one must, as an extra precaution, wait until the appearance of three small stars (OC 235:1). On Motzaei Shabbos, the requirement of tosefes Shabbos necessitates waiting until these small stars appear adjacent to each other in the sky (293:2). Based on this, contemporary calendars generally present -8.5 degrees as the standard time to end Shabbos; this is approximately when melachah was resumed after Shabbos in prewar Europe and other communities. Perhaps Rabbi Notis believes that his calculations render the precaution of waiting for small stars obsolete, but it is no small thing to chop off time from Shabbos as practiced for generations.6
Another reason to question Rabbi Notis’s zeman for tzeis is that the onset of bein hashemashos may not correspond exactly to what we call sunset. Although we associate sunset with the disappearance of the ball of the sun below the horizon, some have argued that Talmudic sunset refers to the sun’s light, not its body, and takes place a bit later.7 If true, this thesis would confirm that tzeis hakochavim cannot be calculated as three-quarters of a mil after what we call sunset.
Furthermore, as Rabbi Notis himself points out (p. 86), the Gemara does not explicitly say that it is tzeis hakochavim that occurs after three-quarters of a mil; rather, the event that occurs at that time is “when the upper part of the sky darkens and equates to the lower.” This is nightfall according to Rabbi Yehudah; Rabbi Yose maintains that nightfall is a bit later.8 While most assume that the difference between the opinions of these two Tannaim is minimal, it would still have been worthwhile to analyze their disagreement more clearly, as well as to discuss whether the phenomenon of “the upper part of the sky darkens and equates to the lower” actually takes place at -4.37 degrees.
Rabbi Notis notes that the exact solar depression angle at which three stars appear fluctuates based on location and season; he explains that the Gemara gave the measurement of three-quarters of a mil as a time that we can be sure three stars have appeared. The suggestion that tzeis could actually occur before -4.37 degrees is remarkable.9 What if, on Motzaei Shabbos, one personally sees three stars early, but one’s neighbor is not looking and plans to rely on the time listed in the luach for -4.37 degrees? Would Rabbi Notis permit the stargazer to end Shabbos and concurrently allow the calendar-user to still begin seudah shelishis? Perhaps the precise nature of the three-quarter–mil figure has not yet been fully understood;10 in any event, both tradition and logic consider observation primary and the mil measurement secondary.
It is noteworthy that Rabbi Notis is much more flexible about the mil times for determining alos hashachar than he is for tzeis. Astronomic dawn occurs when the sun is 18 degrees below the horizon. Rabbi Notis accepts this figure for halachah although it does not correspond to the Gemara’s figure of four mil before sunrise (unless we assume a different measurement of the mil and/or a different definition of sunrise—neither of which Rabbi Notis is inclined to do, preferring instead to consider the Gemara’s figure the result of “rounding” [p. 169]).
Rabbi Notis writes with a confidence that implies that virtually all the issues surrounding the interface of astronomy and halachah are now solved; I do not share this certainty. It is beyond the scope of this review to document every point in the book that requires further discussion; most pressing, in my view, is countering the possibility that a reader might come away with a willingness to end Shabbos twenty minutes after sunset. While this book is an invaluable resource to better understand a complex topic, one should take its definitive halachic pronouncements with a grain of salt.
Notes
1. He also correctly argues in favor of shaos zemaniyos being calculated from sunrise to sunset; oddly, however, he ignores one of the most compelling proofs for this, which is that the main instrument for telling time in the period of Chazal was a sundial.
2. Rabbi Notis does not cite the view that there are 40 mil from sunrise to sunset, which would justify the 18-minute mil (see Chazon Ish, OC 13). He also is too quick to dismiss the difficulties that are posed to these figures by the actual amount of time it takes a person to walk a mil (see p. 131). (It should be noted that mil is properly a measurement of distance; the term is also used to describe the amount of time it takes to walk that distance.)
3. See, e.g., Responsa Yabia Omer, OC 7:41.
4. Rabbi Notis completely adopts the narrative that the Geonim and Rabbeinu Tam had diametrically opposed opinions, while at the same time acknowledging that the posekim and communities that followed Rabbeinu Tam determined tzeis by observation of three stars. He does not fully address the conceptual difficulty with this, or cite alternative explanations of Rabbeinu Tam such as those proposed in Yom Valaylah Shel Torah by Rabbi Y.G. Weiss (which Rabbi Notis cites in a different context [p. 159] while ignoring Rabbi Weiss’s main thesis). See also Rabbi M.M. Karp’s monograph in the back of Mishmeres Shabbos (printed in Hilchos Shabbos B’Shabbos, vol. 4). Even if he disagrees with their arguments, Rabbi Notis should not have glossed over the issues they raise.
5. An ancient Ashkenazic mesorah, based on one reading of the Yerushalmi (Berachos 1:1), holds that the “medium” stars are those that appear close together, which puts tzeis at about -7 degrees. See HaZmanim BaHavanah by Rabbi Hirsch Lampin, chap. 2. In general, Rabbi Notis would have benefited from reading and citing this excellent book.
6. At the end of the book, Rabbi Notis throws in a non sequitur that it is “praiseworthy” to end Shabbos 40–50 minutes after sunset in New York (p. 182), i.e., -8.5 degrees. One wonders what his basis for this statement is when waiting such an amount of time after sunset is double what he requires and contradicts his entire thesis. Of course, I consider this zeman for ending Shabbos not “praiseworthy” but obligatory.
7. See Ohr Meir by Rabbi Meir Posen, and Rabbi Karp’s monograph cited above, n. 4. See also Rabbi Y. Kapach’s commentary to Rambam, Hilchos Shabbos, chap. 5, n. 14. There are some difficulties with this approach as well, but it should at least increase our hesitancy about adopting an early tzeis in contravention of historical practice.
8. Indeed, halachah may fundamentally take the opinion of Rabbi Yose into account (see, e.g., Biur HaGra, OC 261 and Biur Halachah 499, s.v. v’chein, Sha’ar Hatziyun 133:21). Rabbi Notis should therefore not have stated unequivocally that minor fast days end at sunset (p. 182), or that concern for Rabbi Yose is only required at the end of Shabbos (p. 164).
9. Furthermore, if tzeis can actually take place before -4.37 degrees, it is difficult to understand why Rabbi Yose would consider halachic nightfall to take place even later.
10. See the writings of Dr. William Gewirtz, especially https://zemanim.net/wp-content/uploads/2020/05/postzemanim.pdf, p. 125.
Rabbi Yaakov Hoffman is the rabbi of Washington Heights Congregation (“The Bridge Shul”) in New York City. He works as a rabbinic coordinator for OU Kosher and associate editor of OU Press.