Today’s daf yomi, Menachot 20b, mentions in passing that the blood of a korban and the kometz become invalid at sunset – בשקיעת החמה. There is a very large Tosafot here (s.v. nifsal) which shortens the daf considerably and makes life easier for us daffers. What is it that Tosafot discusses at such length? It is the question of when sunset halakhically occurs. While this seems to be a bizarre question – sunset occurs at sunset! – it actually is one that engaged many Rishonim and plays an important role in the halakhic definition of night.
Here’s the problem. The Gemara in Shabbat (35a) states that the period of dusk – בין השמשות – which has the status of “doubtful day and doubtful night” begins at sunset and extends until the time it takes to walk 3/4 of a mil (approximately 1 km). If we assume (as other Gemarot indicate) that it takes 18 minutes to walk a mil, this would mean that בין השמשות would extend from sunset until 13.5 minutes afterwards and then it would be night. This would mean that Shabbat would get out 14 minutes after sunset!
That is one Gemara. There is another Gemara, however, one in Pesachim (93b) which discusses the astronomical question of how thick the rakiya – the sky – is. The Gemara assumes that the רקיע is a thick opaque dome that covers the Earth (which is flat, by the way). The sun rises in the east, sets in the west, then travels through the thickness of the rakiya (there is a window or tunnel in it for the sun to pass through) and at night travels over the rakiya from west to east, so that it can pass through the thickness of the rakiya again the next morning. How long does it take for the sun to pass through the rakiya, asks the Gemara? The Gemara answers – from the time of amud hashachar, the morning star and when it starts to get light, until sunrise, and this is the time it takes to walk 4 mil, in other words, 72 minutes.
This makes sense, given the cosmology, since the light that we see before sunrise is, according to the Gemara, the light that is emitting from the tunnel in the rakiya once the sun has entered it. And, indeed, we rule that amud hashachar occurs 72 minutes before sunrise. The Gemara adds to this, however, that this is also the same time it takes from sunset until צאת הכוכבים, from the time the sun goes down until – apparently – all light leaves the sky, since that occurs when the sun has exited the western tunnel in the rakiya.
So now we have two Gemarot. One that says that night comes 13.5 minutes after sunset, and one that says that it comes 72 minutes after sunset. How to reconcile them? The Geonim (see Otzar HaGeonim, Shabbat 35a), and Rambam (Shabbat 5:4) assume that the Gemara in Shabbat is the authoritative one, since it is directly addressing itself to the halakhic question of when night begins. How would one explain the Gemara in Pesachim? The Vlina Gaon states (on Shulkhan Arukh 261:2) that this Gemara is not asking a halakhic question, but an astronomical one, and the question is not when 3 stars come out (which defines night), but when all the stars come out. The significance of all the stars coming out is that – according to this cosmology – the stars are distributed throughout the thickness of the rakiya, and they descend slowly through the thickness, until they reach the inner surface and are visible. Thus, when all the stars come out is when the ones on the top have travelled through the thickness of the rakiya. When all the stars come out, then, is equivalent to the time it takes the sun to travel the thickness of the rakiya (assuming the sun and stars travel at the same speed).
The Vilna Gaon rules in favor of this approach, and according to him Shabbat should end 14 minutes after sunset on Saturday night. However, even in Yerushalayim where they adopt the practices of the GR”A, 14 minutes is a little too soon for comfort, and the standard practice is 25 minutes after shkiya.
Rabbeinu Tam, however, focused on the Gemara in Pesachim and ruled that Shabbat is not over until 72 minutes after shkiya. How, then, to explain the Gemara in Shabbat that speaks about 13.5 minutes after shkiya? This, says Rabbenu Tam, is not when the sun sets, but a second shkiya, presumably when the sun begins exiting the western tunnel in the rakiya. Until that second shkiya it is fully day, and bein hashemashot begins from the second shkiya – 58.5 minutes after sunset, and ends 72 minutes after sunset. Thus, Shabbat would not begin on Friday until 58.5 minutes after sunset, and would not end on Saturday night until 72 minutes after sunset! Surprisingly, this position is adopted by many Rishonim, including Ramban, and is how Shulkhan Arukh rules (Orah Hayim 261:2). While in the past there were definitely people that paskened Rabbenu Tam even li’kula, and did melkaha on Friday after sunset, nowadays, no one has the temerity to rely on this position and suggest that Shabbat does not begin at sunset. However, there are those – including this author – who are strict like Rabbeinu Tam and do not end Shabbat until 72 minutes after sunset.
Why did Rabbenu Tam give preference to the sugya in Pesachim. We cannot know for sure, but one possibility is that he was influenced by how he experienced nightfall. France is located at 46º latitude, whereas New York, NY, in contrast is located at 40.5º latitude. This makes a huge difference in terms of when sunset occurs and how long it takes to get dark after sunset. As the latitude gets closer to the poles, the length of dusk, i.e., the time it takes to get dark, can extend significantly. (See the related article in Wikipedia on this point.) Thus, Rabbenu Tam could not accept that it was night a mere 14 minutes after sunset, and took the Gemara in Pesachim to be the authoritative source. In contrast, in Israel – which is located at 31º-32º latitude, it gets dark very quickly after sunset, and it is easier to accept the GR”A position that it is night 14 (or 25) minutes after sunset.
[It is worth noting that the GR”A was explaining a Gemara that was referring to Jerusalem, so this works out very well in the text. Interestingly, the latitude of Vilna is even higher than that of France – 54º latitude. The GR”A position is totally a function of the sources, and not the reality as he must have observed it.]
The general psak followed in America is neither of the GR”A or Rabbenun Tam, but a compromise position of anywhere from approximately 42-50 minutes. On the one hand, this reflects the reality in most US cities, which are situated latitudinally somewhere between Israel and France. The way this is explained halakhically (bracketting the position of Rav Moshe Feinstein) is that because we cannot resolve the debate of Rabbenu Tam and the GR”A, we will go by the straight observation of 3 medium-sized stars. Thus, after 45 minutes or so, stars are visible across the sky, and we can assume that there are 3 medium-sized stars, so we can rule that it is צאת הכוכבים. Thus, for us, בין השמשות starts at sunset and ends 45 minutes or so afterwards.
In the next post we will discuss the significance of the first sunset according to Rabbenu Tam and post links to related resources on this topic.