Question: What is Bein ha'Shemashos?

Answer (R. Tanachuma): It is like a drop of blood on the edge of a sword - the drop is divided, [part goes] to here (on one side, and [part goes] to here. This is Bein ha'Shemashos (it is a Safek - part is day, and part is night - R. SHLOMO SIRILIYO).

What is [the duration of] Bein ha'Shemashos? It is from Shki'ah until the amount of time needed to walk half a Mil. R. Nechemyah says so;

R. Yosi says, Bein ha'Shemashos is [as long as] the blink of an eye. Chachamim could not determine [the exact moment].

R. Yosi (the Amora) and R. Acha were sitting.

R. Yosi: It is not reasonable that the end of the [time to walk a half-Mil] of R. Nechemyah, [then] is the eye's blink of R. Yosi?

R. Acha: Also I hold like this.

R. Chizkiyah did not say so. Rather, every eye's blink in the half Mil of R. Nechemyah, is a Safek [according to R. Yosi. He does not know when Bein ha'Shemashos is within that time period.]

Question (R. Mana, to R. Chizkiyah): We learned a Mishnah there, if a man saw one [emission of Zivah; it is distinct from semen] during the day and one Bein ha'Shemashos, or one Bein ha'Shemashos and one during the day - if he knows that part of the sighting [Bein ha'Shemashos] was today (during the day) and part was the next day (i.e. at night, it is considered like two sightings, so), he is Vadai a Zav for Tum'ah and for Korban (he had three sightings within a clean day in the middle);

Note: The question will be explained below.

If it is a Safek if part was today and part was tomorrow (or it was all today or all tomorrow), he is Vadai a Zav for Tum'ah (he had at least two sightings without a clean day in the middle) and a Safek for Korban (three sightings are needed for Korban).

Question (R. Chiya bar Yosef, to R. Yochanan): Who is the Tana who holds that one sighting is divided into two (if it was on two days)?

Answer (R. Yochanan): It is R. Yosi. (According to R. Nechemyah, we could know that a sighting was on two days only if it lasted more than the time to walk a half-Mil. This is more than the time to immerse and dry, so all agree that it is considered multiple sightings even if it was on one day!)

Summation of R. Mana's question: This is difficult for you. You say that every eye's blink in the half Mil of R. Nechemyah, is a Safek [according to R. Yosi]. Why [does the Beraisa say 'if he knows that part was today and part was tomorrow'? You cannot say that the sighting endured the entire Bein ha'Shemashos of R. Nechemyah, like we explained above!]

R. Mana: [R. Chizkiyah] answered me, if Eliyahu will come and say 'this is Bein ha'Shemashos' (we can know that the sighting was on both days. We explained this like R. SHLOMO SIRILIYO, CHAREDIM.)

R. Mana: I asked him, when Eliyahu will come and say 'this is Bein ha'Shemashos', who argues?! (Why did R. Yochanan say that our Mishnah is R. Yosi? Rather, this shows that R. Yosi was sure when his Bein ha'Shemashos begins. - NO'AM YERUSHALMI, SEFER NIR. Also, if Eliyahu will clarify, why does the Seifa say 'if it is a Safek'? - R. SHLOMO SIRILIYO, HA'GAON RAV C. KANIEVSKY, SHLITA.)

Question (R. Chanina, the friend of Rabanan): Just like you say at night, that when three stars are seen, even though the sun is in the middle of the Raki'a, it is night - even in the morning you should say so!

Note: Below we say that there is time to walk four Mil between He'ir ha'Mizrach (when the eastern sky lights up) and sunrise, and Pesachim 93b says so about between sunset and Tzeis ha'Kochavim. During this time, the sun passes through Raki'a; we do not see the sun, but it partially illuminates the sky. Most explain the Yerushalmi like R. Tam. 'Shki'ah' is not sunset, rather, the setting of the sun's light.

Answer #1 (R. Aba): It says "ha'Shemesh Yatzah Al ha'Aretz v'Lot Ba Tzo'arah", and it says "u'Va ha'Shemesh v'Taher" - this equates the sun's exit [from the Raki'a in the morning] to its entrance [to the Raki'a at night]. Just like its entrance, when [its illumination] is covered from people (and we see stars, it is night) so its exit, when it is known to people (it enters the Raki'a and illuminates, it is day).

Answer #2 (R. Aba): It says "ha'Boker Or" - the Torah called [when it is] light 'morning'.

(Beraisa - R. Yishmael): "Ba'Boker Ba'Boker" gives a limit to the morning (beginning) of the morning (i.e. dawn).

Question (R. Yosi bei R. Bun): If I say to give [the time when the sun passes through] the thickness of the Raki'a to the night, whether at [the start of the] night, or (PF) in the morning, it turns out that the day and night are not equal (at the equinoxes, i.e. the days when the sun rises due east. The day will be longer than the night. A Beraisa refutes this!)

(Beraisa): On the first day of Tekufas Nisan and Tekufas Tishrei (the equinoxes), the day and night are equal.

Answer (to both questions - Rav Huna): (The Beraisa does not discuss Halachic day and night. Rather, it teaches that on the equinoxes, the sun is visible and hidden for equal amounts of time, i.e. 12 hours each.) We learn [Halachic day and night] from earthly conduct. When the king starts to leave (his palace), even though he did not leave, they say that he left. When he starts to enter, we do not say that he entered until he [truly] enters. (In the morning, once the sun exits from under the Raki'a and enters the Raki'a, we say that it left, and it is day. In the evening, once the sun [goes below the horizon and] enters the Raki'a, we do not say that it left, and it is not night until it passes through the Raki'a. We explained this based on, but not totally like, EVEN HA'EZEL, Hilchos Keri'as Shma 1:3.)