When it might be day or night, which time is twilight (which is the time it takes to walk three quarters of a mil after sunset, when [the time it takes to walk] a mil is one third of an hour less 99 seconds), one may not tithe produce which is definitely untithed, one may not immerse utensils [in a mikveh], one may not light the candles, nor may one create an eruv for the town. But one may tithe produce which may have been tithed, one may put food in the oven, and one may create an eruv for the apartment block. During twilight one may tell a non-Jew to light lights for Shabbat and to do any task which may be needed for a mitzvah or which is causing one concern. Note: Likewise, one who brought in Shabbat and hour or two before dark may tell a non-Jew to light the lights and the other things that are necessary.
We now come to the very last moments before Shabbat begins. Contrary to popular belief, there is no set time of the clock at which Shabbat begins, but the matter is dependent on the amount of natural darkness on any particular day and - as we shall see in the next shiur - on local custom. Rabbi Karo here gives a definition which is not universally accepted; indeed a different - and more simple - method of determining the end of the day is now almost universally accepted.
We could put the matter very simply if we were to say that Shabbat begins the moment Friday ends. But that would be a tautology which begs the question. What we need to know is at what time a new day is considered to have begun according to Jewish tradition. The Torah [Genesis 1:5] tells us that from the very beginning of time the evening comes before the morning:
And there was evening and there was morning - a first day.
Thus Shabbat must begin when darkness falls and night begins on Friday. However, as we all know, this does not happen 'in the twinkling of an eye', but there is a period between day and night which we call twilight. Twilight begins with sunset, because as the sun seems to dip further and further below the horizon daylight lessens and darkness increases. But at what point may we assume that twilight has ended and true night has begun?
I must emphasize at this point that for the purposes of Shabbat this issue is now irrelevant since it is universally accepted that Shabbat must begin before darkness sets in, as we shall see in the next shiur. However, for the sake of completeness let us briefly review the halakhic situation concerning the onset of darkness. The very first mishnah [ Berakhot 1:1] fixes this time as 'star-rise', the time when the sky is dark enough for three medium-size stars to become visible. However, this, of course, is a variable; for the time when three stars will be visible in the night sky will depend (among other imponderables) on the state of the weather, the eyesight of the spectator and the magnitude of the stars. To further complicate matters, the sages are wont to distinguish between 'small' stars, 'medium' stars and 'large' stars. It is obvious that since they could have had no concept of magnitude, they must be referring to the luminosity of the stars. Clearly, the visibility of stars is intended to indicate varying degrees of the onset of darkness. 'Large' stars don't count, because they can be seen even before it is dark. The end of Shabbat (which requires an additional amount of non-sacred time to be added on to the sacred time of Shabbat [tosefet]) requires the visibility of three 'small' stars. For the purposes of reciting the Shema 'at the end of the day' the visibility of three 'medium' stars suffices. When we try to give these indications quasi-scientific determinae, we usually describe them in terms of the sun's declination below the horizon. Three medium stars are deemed to be visible when (at any given geographic location) the sun has declined 5.88° below the horizon; three small stars are deemed to be visible when the sun has declined 8.5° below the horizon. In 'real' terms the former occurs about 25 minutes after sunset and the latter about 40 minutes after sunset.
If, for the sake of argument, we have defined the onset of darkness as the moment when the sun has declined almost 6° below the horizon it is clear that that must also be the moment which determines the end of twilight. However, in earlier ages most people were not able to determine the position of the sun after sunset with such accuracy so the time was defined in terms of "how long it takes to walk" a certain distance. The mil is obviously derived from the Roman 'mile' which originally indicated mille pasuum - one thousand paces. Since the Roman military machine marched at a 'regulation pace' it was possible to calculate the passage of time thereby. The rabbinic 'mil' is calculated as being 1184 metres and that it can be marched in 18 minutes. (That works out as a pace which is just under 4 kph.)
Karo says that twilight is "the time it takes to walk three quarters of a mil after sunset, when the time it takes to walk a mil is one third of an hour less 99 seconds". One third of a standard hour is the equivalent of 20 minutes. Thus Karo would seem to be putting the onset of twilight at just more than 18 minutes after sunset. This is certainly a lot less time than when the sun is almost 6° below the horizon, which occurs about seven minutes later. As I have already indicated, all this is now purely academic, since Shabbat is now deemed to begin much earlier - as we shall see in our next shiur.
Karo indicates that the period of twilight - however we may determine its parameters - is a time when certain final preparations for Shabbat may or may not be done. In our previous shiur I mentioned that foodstuffs grown in Eretz-Israel may not be eaten if they have not been tithed, and I now add that foodstuffs may not be tithed on Shabbat. During twilight foodstuffs known to be definitely untithed may not be tithed, but foodstuffs which need to be tithed because of doubt - they may or may not have been tithed - may be tithed at this time. Broadly speaking, cooking utensils which are made of metal or glass and which were produced by a non-Jew must be dipped into a mikveh [ritual bath] before they may be used in a Jewish household; this may not be done during the twilight period.
There are two kinds of eruv mentioned in the first paragraph of Section 261. The Hebrew term eruv indicates a boundary, but this is not the most appropriate place to go into the minutiae of the various forms and usage of the eruv. Broadly speaking, one form of the eruv will determine the furthest boundary of the town or village in which one lives; on Shabbat one may not travel beyond this boundary. This boundary may not be physically determined on Shabbat itself nor during the twilight period on Friday. Another form of eruv is one which will permit the carrying of objects from one apartment to another within the same apartment block. Such a eruv, says Karo, may be effected during the twilight period on Friday. I repeat and re-emphasize that none of this is relevant nowadays and none of these tasks may be performed after sunset on Friday.
Strictly speaking, anything that a Jew may not do himself or herself on Shabbat he may not ask a non-Jew to do for him. Karo says that this rule may be slightly relaxed during the twilight period on Friday if the task is essential for enjoying Shabbat.
I realize that some of the descriptions of the terms found in this shiur may have left participants with more questions than understanding. I am always wary of giving too much information and I rely on the participants to send me their questions and comments where further elucidation is required.
Ĥag Samé'aĥ to everybody.