Saturday 13 January 2018

The Twilight Zone

Introduction

Few halachic questions come up as often as the one about when the day starts. Once a week all religious Jews ask “When does Shabbos come in?” (except in the summer for those who bring it in early at the same time), and a day later they ask “When does Shabbos go out?” Every day our davening times are affected by the same question, and at times like Chanuka things get even more confusing.

For this reason, I am sure that virtually all readers will have at least some knowledge of the topic. Some will also know how complex the issue is in the gemara and commentaries, and hopefully some will also know enough to argue with some of my conclusions.

Sunset and Stars

We first need to state an assumption which may be obvious for most. The halachic day (24 hours) starts at the beginning of the night.[1] Thus the critical question is when the night starts.

The gemara derives that the halachic daytime goes from Alos Hashachar (dawn) until the stars come out. Thus mitzvos such as circumcision, which must be done during the day, have to be done during this period.[2]  From here it would seem that we just need to define more clearly what ‘the stars coming out’ means, and this time will be the start of the next day.

The reality is not that simple. Elsewhere we are introduced to the concept of Bein Hashmashos (literally ‘between the suns’), a time when uncertainty exists whether it is day or night. Several opinions exist in the gemara, but for the purposes of simplification here we will present just the view of R’ Yehuda, according to Rabba (the view that is accepted in halacha, at least for most purposes).

Once the sun sets, we have entered Bein Hashmashos. This continues as long as there is redness on the western horizon, and even after the bottom part of the horizon has darkened. Only when the top part of the horizon has darkened to the same degree as the bottom part, we can be sure that it is night. The length of Bein Hashmashos is the time that it takes to walk three quarters of a mil (mil= 2000 amos, about 960 metres).[3]

The gemara continues with another way to tell the difference between day and night. If only one star can be seen, it is definitely still day. If two can be seen, it is Bein Hashmashos. If three can be seen, it is definitely night. The gemara clarifies that the stars referred to are not the big ones that can be seen even during the day (perhaps a reference to Venus), nor the small ones that can only be seen well into the night. Rather, we are referring to medium-sized stars.[4]

Tosfos point out the seemingly clear contradiction. If, as the gemara says in one place unambiguously, night starts when the stars come out, why elsewhere are we told about a doubtful period? They answer that the uncertainty is over the very definition of ‘the stars coming out,’ as is explicit in the gemara that there are different sizes of stars.[5] The implication is that from sunset there is already a doubt whether ‘the stars have come out.’[6]

The Rambam writes that the period between sunset and the appearance of three medium-sized stars is called Bein Hashmashos in all places.[7] Understandably, when formulating most of the other halachos dependant on day and night he gives no further explanation, relying on the definition given already.

However, there is one exception. In Hilchos Kiddush HaChodesh, the Rambam states the halacha that the declaration of the new month can only be done during the day.[8] Here he clarifies that this declaration can be made until two stars have come out. After this it is too late (as it may already be night), and the declaration has to wait until morning.[9] What is special about Kiddush HaChodesh?[10]

The Maharalbach explains that only when it comes to Kiddush HaChodesh can we rely on stars to determine when the day has ended, as this mitzvah is under the jurisdiction of Beis Din. Due to the difficulty in determining exactly when the right stars come out, we need a clearer measurement for mitzvos that all are responsible for. Thus from sunset we must be concerned that the next day may have already started. However, when it comes to Kiddush HaChodesh, Beis Din can know that it is still day even after sunset.[11]

How long is a mil?

Even after we have been given sunset as a clear indicator of the start of Bein Hashmashos, we are left with the appearance of three stars as the indicator of the end of it.[12] However, as we mentioned already, Chazal did tell us that Bein Hashmashos lasts the time it takes to walk three quarters of a mil. If we can determine how much time this is, now that we have clocks we should be able to pinpoint Bein Hashmashos exactly.

Theoretically, one way to do this would be to use the time that it takes an average person to walk three quarters of a mil (about 740 metres[13]). This would give us a time of about nine minutes. However, this is impossible for many reasons. Firstly, nine minutes after sunset no-one can see three stars. Secondly, as we will see this would not fit with what the gemara says elsewhere. We must conclude that in the time of Chazal people did not walk as fast as they do now.[14]

The truth is that how long it took to walk a mil in the time of Chazal can be extrapolated directly from another section of the gemara.[15] Rabbah bar bar Chana says in the name of R’ Yochanan that an average person can walk 10 parsa (parsa= 4 mil) in a day. The first 5 mil are walked from Alos Hashachar until sunrise, and the last 5 mil are walked between sunset and the stars coming out.

However, this statement is refuted by a braisa (Mishnaic period source) that says that only 4 mil are walked between Alos Hashachar and sunrise, and another 4 mil between sunset and the appearance of stars.[16] Thus the time taken for the sun to pass through the ‘thickness of the sky’ is a tenth of the length of the day.

The gemara concludes that although the statement of R’ Yochanan as given above is definitely problematic, it is possible that a more accurate version of his statement is correct. It could be that R’ Yochanan “only spoke about the day, and the rabbis made a mistake in calculating the time before and after.” How we understand this correction of the original statement is critical.

Rashi explains that R’ Yochanan merely said that an average person walks 10 parsa a day, and did not specify when they start or finish walking. In fact they usually start before Alos Hashachar and finish after the stars have appeared, allowing them to walk 5 mil before sunrise and 5 mil after sunset. Between Alos Hashachar and sunrise, and between sunset and the stars appearing, there is only enough time to walk 4 mil.

With this information, calculating the time taken to walk a mil is relatively simple. Assuming that the gemara is talking about the average day, with 12 hours between sunset and sunrise,[17] it takes 12 hours to walk 8 parsa (one parsa is walked before sunrise, and another parsa after sunset). Thus it takes one and a half hours to walk one parsa, or 22.5 minutes to walk a mil. So Bein Hashmashos is three quarters of 22.5 minutes, just under 17 minutes.

The Vilna Gaon explains differently. R’ Yochanan really meant that a person walks 10 parsa in the 12 hours between sunrise and sunset, but he was misinterpreted to include the time before sunrise and after sunset. Thus each parsa takes 72 minutes to walk, and each mil 18 minutes. The length of Bein Hashmashos is three quarters of 18 minutes, 13.5 minutes.[18] [19]

The Rambam writes that one can walk 15 mil between sunrise and midday (6 hours).[20] According to this a mil takes 24 minutes to walk,[21] so Bein Hashmashos is three quarters of this, 18 minutes. This position seems difficult, being in accordance with the original version of the statement of R’ Yochanan which the gemara rejected.[22]

Practical Application

Whether Bein Hashmashos is 13.5, 17 or 18 minutes, there seems to be a problem when it comes to translating this into reality. Even in Eretz Yisrael, we generally see three stars only about 25 minutes after sunset[23] (this increases further from the equator).

Even if we do accept a length of Bein Hashmashos of 17-18 minutes (13.5 is usually discounted as being unrealistic), this is certainly not uniform. As the Vilna Gaon points out, the length varies during the year, and with altitude.[24]

In order to achieve logical times for the whole year in all places, many suggest that we assume a Bein Hashmashos of 18 minutes at sea level, at the equinox in Eretz Yisrael.[25] We should measure how many degrees the sun is below the horizon 18 minutes after sunset, and extrapolate that at all times and in all places, ‘the stars come out’ when the sun is this number of degrees below the horizon.[26]

In my eyes, the big problem with this is that the gemara glaringly omitted to mention any difference based on time of year or altitude. To assume that the gemara spoke specifically at the equinox and at sea level seems fanciful. The problem is magnified by the fact that some of the differing views in the gemara disagree over only a few minutes, implying that they believed the times they were giving were to a high degree of accuracy.

It is interesting to note that as we quoted above, the Rambam in Hilchos Shabbos tells us only that Bein Hashmashos is until the stars have come out, and does not say how long this is. Elsewhere he tells us vaguely that it is ‘about a third of an hour.’[27] It could be that he was aware that the times given in the gemara are not 100% reliable, and to be safe we should check for the stars ourselves.

I conclude that although the halachic calendars we have are immensely helpful, we should be aware that they are not the final word. While the times given for the end of Shabbos usually include enough stringency to make them reliable, the more sophisticated calendars that give times that appear to be exceedingly accurate are probably not. When it comes to mitzvos like saying Shema at night, or deciding which day a baby boy was born for the purposes of fixing when the Bris will be, great care must be taken.



[1] Although Rashbam in his commentary to Bereishis 1:5 (in uncensored versions) seems to dispute this, his explanation was only meant on the level of pshat (simple meaning) and not halachically. This is clear from his introduction.
[2] Megila 20b, from a verse in Nechemia 4:15
[3] Shabbos 34b
[4] Ibid. 35b
[5] Megila 20b ד"ה והא, Pesachim 2a ד"ה והא
[6] Although based on other comments of Tosfos, the ‘sunset’ they are referring to is not what it seems. They accept the explanation of Rabeinu Tam, that sunset here means ‘the end of the sunset’, which is much later than what we call sunset. Throughout this post we have assumed the position of the Vilna Gaon (and the Geonim), who rejects the view of Rabbeinu Tam as it does not fit with reality.
[7] Hilchos Shabbos 5:4
[8] When there is a Sanhedrin, for the start of the new month to be on the thirtieth day from the previous new month, it was necessary to first accept testimony about the sighting of the new moon and then for the Sanhedrin to designate that day as Rosh Chodesh.
[9] Hilchos Kiddush HaChodesh 2:9. Although there is a seeming internal contradiction within this halacha, almost all the commentators I have seen explain that the cut-off point is two stars, and based on the gemara this must be the case. See for example Biur Chadash Maspik.
[10] According to the Rambam sunset cannot be synonymous to the appearance of two stars (similar to the answer of Tosfos above), as if this was the case he would not have needed to give a different indicator of Bein Hashmashos to the normal one.
[11] Shu”t Maharalbach siman 144. He explains that the appearance of two stars sometimes occurs immediatetly at sunset, but it can be up to a twelfth of a mil (one and a half to two minutes) later than this.
[12] This is not a difficulty with the explanation of the Maharlbach, as one who cannot discern three stars will remain in doubt until he can. It is only critical to have a clear indicator of the beginning of  Bein Hashmashos, so that people do not erroneously think it is still day when they fail to notice the stars. See Piskei Ri’az, Shabbos 2:4 (paragraph 8) who says that the indicator of the appearance of stars was given only as a stringency and cannot be relied on to be lenient.
[13] As you might expect, this is also an issue of a debate and according to some poskim it is as much as 864 metres. The figure given above is the more accepted one (and also the more realistic one, but showing this would require another post).
[14] This fact can be supported by other evidence from sources in halacha and elsewhere, but there is a limit to what I can write here.
[15] Pesachim 94a
[16] The commentaries point out the seeming major contradiction between this and the three quarters of a mil measurement given above, a problem I have not dealt with here.
[17] Many early poskim mistakenly believed that the average day has twelve hours between Alos Hashachar and the appearance of stars, throwing these calculations off. See Levush, Orach Chaim 267:2 and Biur HaGra, Orach Chaim 459:2 who point out this mistake.
[18] Biur HaGra ibid. He brings support for this from the Rambam’s commentary to the first Mishna in Berachos. Here the Rambam says that the time between Alos Hashachar and sunrise is 72 minutes (although it seems that the Rambam retracted from this position, as we will explain).
[19] It is worth noting that the Gra in Orach Chaim 261:2 writes that the statement that one star is day, two Bein Hashmashos and three night, is according to the differing view of R’ Yosi. His position is that Bein Hashmashos does not start at sunset, but 13.5 minutes later (according to the Gra), and lasts only for ‘the twinkling of an eye.’
[20] Hilchos Korban Pesach 5:9
[21] A position stated also in his commentary to the Mishna in Pesachim 3:2
[22] The Gra writes that the Rambam must have had a different text of the gemara.
[23] Although some have claimed that people with astronomical knowledge do know where to see stars at the appropriate times. See this article (in Hebrew) for details.
[24] Places that are high up (like Yerushalayim) see sunset later, but the appearance of stars is unaffected by altitude. Thus Bein Hashmashos is shorter at higher altitudes.
[25] The equinox is chosen in order to achieve 12 hours between sunrise and sunset.
[26] At the equinox Bein Hashmashos is at its shortest. Using this method means that in the middle of the winter and in the middle of the summer, Bein Hashmashos in Eretz Yisrael at sea level is 24 minutes.
[27] Hilchos Trumos 7:2. This fits with the time of 18 minutes that follows from what he wrote in Hilchos Korban Pesach.

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