Rather, it must be that the reference is with regard to eating teruma. Priests may not eat teruma until twilight is completed, which according to Rabbi Yosei’s opinion is slightly later than it is according to Rabbi Yehuda’s opinion.

With regard to the period of twilight, Rav Yehuda said that Shmuel said: When one can see one star in the evening sky, it is still day; two stars, twilight; three stars, night. That was also taught in a baraita: When one can see one star in the evening sky, it is still day; two stars, twilight; three stars, night. Rabbi Yosei said: This is neither referring to large stars that are visible even during the day, nor to small stars that are visible only late at night. Rather, it is referring to medium-sized stars.

Rabbi Yosei, son of Rabbi Zevida, said: One who performs a prohibited labor during two twilights, one between Friday and Shabbat and one between Shabbat and the conclusion of Shabbat on Saturday night, is liable to bring a sin-offering for performing a prohibited labor on Shabbat whichever way you look at it. Whether we say that twilight is day or night, certainly one of those labors was performed on Shabbat. Rava said to his servant: You, who are not expert in the measures of the Sages, when the sun is at the top of the palm trees, light the Shabbat lights. His servant asked him: What should we do on a cloudy day, when the sun is not visible at the top of the trees? Rava said to him: In the city, watch the roosters because as evening approaches they sit on their beams. In a field, watch the ravens because they return to their nests as evening approaches. Alternatively, you can watch the plants [adanei] that turn westward in the evening. When they begin to turn westward evening is approaching.

The Sages taught in a baraita: They sound six blasts on Shabbat eve to announce that Shabbat is approaching. The Gemara details what each blast signifies. The first blast is in order to stop the people from work in the fields. The second blast is to stop those who are working in the city, and to inform the proprietors to close the stores. The third is to inform them to light the Shabbat light; that is the statement of Rabbi Natan. Rabbi Yehuda HaNasi says: The third blast is to inform those who don phylacteries throughout the day to remove their phylacteries, as one does not don phylacteries on Shabbat. And he pauses after the third blast for the length of time it takes to fry a small fish or to stick bread to the sides of the oven. One who forgot to do so and needs those foods for Shabbat may do so then. And he sounds a tekia, and sounds a terua, and sounds a tekia, and he accepts Shabbat. It is then that Shabbat begins in every sense.

Rabban Shimon ben Gamliel said: What shall we do to the Babylonian Jews? They stray from the custom, as they sound a tekia and a terua, and they accept Shabbat during the terua, i.e., upon hearing the blast of the terua. The Gemara asks about this: Do the Babylonians really sound only a tekia and a terua and no more blasts? If so, there are only five blasts and not six, as it was taught in the baraita. Rather, the correct version is: They sound a tekia, and they again sound a tekia, and then they sound a terua, and they accept Shabbat during the terua. They do so because they continue the custom of their fathers that was handed down to them.

Rav Yehuda taught to Rav Yitzḥak, his son: The second blast that is sounded before Shabbat is to inform people to light the light. The Gemara asks: In accordance with whose opinion did he say this? It is neither in accordance with the opinion of Rabbi Natan nor in accordance with the opinion of Rabbi Yehuda HaNasi. Rather, certainly he told him that the third blast is in order to inform people to light the light, and in accordance with whose opinion did he say this? It is in accordance with the opinion of Rabbi Natan.

On a similar note, the school of Rabbi Yishmael taught in greater detail: Six blasts are sounded on Shabbat eve. When one begins sounding the first tekia, the people standing and working in the fields refrained from hoeing, and from plowing and from performing all labor in the fields. And those workers who work close to the city are not permitted to enter the city until those who work farther away come, so that they will all enter together. Otherwise, people would suspect that the workers who came later continued to work after the blast. And still, at this time, the stores in the city are open and the shutters of the stores, upon which the storekeepers would arrange their merchandise in front of the stores, remain in place. When he began sounding the second blast, the shutters were removed from where they were placed and the stores were locked and in the homes, however, hot water was still cooking on the stove and pots remained in place on the stove. When he began sounding the third blast, the one charged with removing food from the stove removed it, and the one charged with insulating hot water for Shabbat so that it would not cool off insulated it, and the one charged with kindling the Shabbat lights lit. And the one sounding the shofar pauses for the amount of time it takes to fry a small fish or to stick bread to the sides of the oven, and he sounds a tekia, and sounds a terua, and sounds a tekia, and accepts Shabbat.

Rabbi Yosei bar Ḥanina, said: I heard that a person who was pressed for time and comes to light Shabbat lights after six blasts may light without concern, as even the moment of the sixth blast is not yet Shabbat. Proof for this is that the Sages provided the sexton of the synagogue a period of time to take his shofar, which he used to sound the blasts on a tall roof in the middle of the city, to his house. Clearly, during that interval it is not yet Shabbat. He said to him: If so, then you have rendered your statement subject to circumstances, and it would not apply uniformly to all. Shabbat would start at a different time in each place based on the distance between the site where the shofar is sounded and the home of the sexton. Rather, Shabbat began immediately after the final blast with no pause in between. The sexton had a concealed place on top of his roof, where he would sound the shofar, in which he would place his shofar because the consensus is that one may move neither the shofar nor the trumpets on Shabbat.

The Gemara asks with regard to this last halakha: Wasn’t it taught in a baraita that the shofar may be moved on Shabbat, and the trumpets may not be moved? Rav Yosei said: This is not difficult, as one could say that here, where moving a shofar was permitted, it is referring to a shofar belonging to an individual. Because it has a use even on Shabbat, it may be moved. There, where moving a shofar was prohibited, it is referring to a shofar that belongs to a community. Because it has no use on Shabbat, it is, therefore, considered set-aside [muktze]. Abaye said to him: And in the case of an individual, for what permitted action is a shofar fit to be used on Shabbat? It is fit for use since it is suitable to give water with it