פירוש על ברכות 4:1

Perhaps it means when the sun rises - the sun should shine on the 8th day and the man should make himself pure by bring his korban and then he can eat.

PERHAPS THE SETTING OF [THE SUN'S] LIGHT. The Gemara on 2a quotes a Baraisa that teaches us that the verse in Vayikra 22, 7, ובא השמש - after the sun has set, וטהר - the day shall pass completely, is teaching us that after the sun sets on the day of immersion, when the stars appear, one becomes tahor and may eat terumah even when the tamei person is required to offer a series of sacrifices on the next day. The word וטהר refers not to the person who becomes tahor, but rather to the sky that is entirely free of any rays of the sun.
The Gemara challenges this derivation. Why is the Tanna so certain that the words ובא השמש mean that the sun has set, perhaps ובא - means the “coming of the light” השמש - of the sun?
But what does “coming of its light” mean? Rashi explains that the Gemara’s question is that perhaps the verse is saying that one must wait until the sun rises the next morning and וטהר means that he must purify himself - the tamei must offer his series of sacrifices in the Bais Hamikdosh and he will first then be allowed to eat terumah.
Tosfos vigorously objects to Rashi’s understanding of the Gemara’s challenge to the Baraisa, as we will now see. Rashi explained that when the Gemara asks: Perhaps
1) the verse ובא השמש - means the “coming of light”, it means till [the sun’s] light will shine on the eighth day. And what does
2) the verse וטהר - and he will be purified mean? It is not a reference to the sky, but rather, the person will be purified. This means: That the person will become purified by offering his sacrifices.
In other words, the Gemara’s challenge is totally rejecting the concept of one becoming purified after sunset of the seventh day and is suggesting that perhaps the verse means that one becomes eligible to eat terumah only after offering the needed sacrifices on the eighth day.
Tosfos has three difficulties with Rashi’s explanation. The first: His explanation is bewildering. For if this is truly a challenge to the ruling that one becomes tahor at sunset of the seventh day, why is this challenge addressed to the Baraisa in our Gemara which explains the verse ובא השמש וטהר, [the Gemara] should challenge that Mishna cited in He’arel (Yevamos 74b), which says, when the sun sets in the west, [the former tamei] may eat terumah etc. How does the Tanna of that Mishna know that the verse is discussing the setting of the sun on the seventh day? Perhaps it is speaking of sunrise the next day? The Gemara should challenge the ruling of the Mishna, rather than the derivation of the Baraisa.
The second question: Tosfos analyzes the words used to describe sunrise. Furthermore, how could the verse possibly be speaking about sunrise? For if it is speaking about sunrise, the verse should have been written as follows: The sun will shine and he must purify himself, as in (Bamidbar 21, 11) “from where the sun shines”. We see that the word זריחה is used to describe sunrise. Or, to describe sunrise, the term “went out” should be used, as in (Bereishis 19, 23) - “The sun went out upon the earth”. Here we see that the verb יציאה-going out is used to describe sunrise. Since the verse uses the expression “the sun will come”, it is apparent that it means sunset. Why would ובא - and it will come be used as a description of sunrise? If יצא is used to describe the ascent of the sun from below the horizon, ובא should be used to describe the descent of the sun below the horizon.
A third question: The Gemara soon debates this issue in a slightly different format. First, the question about whether “coming of the sun” means sunset or sunrise (according to Rashi) is asked. The Gemara finds the answer in a Baraisa that speaks of the time of the recital of Shema as the time when the stars appear. This is fairly close to sunset, so “coming of the sun” must mean sunset. But according to Rashi’s explanation of the Gemara’s question, that the alternative to sunsetr is sunrise, the answer is quite evident from a Mishna. Why introduce a Baraisa to prove this point?
Furthermore, soon [the Gemara] will ask: if this expression “the sun will come”, means “coming of its light”, which according to Rashi means sunrise. [The Gemara] solves this query from a Baraisa which says that a reminder of the time that one may eat terumah after immersion is when the stars become visible etc. Since the Baraisa refers to this time as the stars coming out, obviously the “coming of the sun” must mean sunset. But why is it necessary to deduce this from a Baraisa? It should be resolved from the Mishna in (Negaim 14, 3) where the Mishna clearly says: when the sun sets in the west, he may eat terumah. The Mishna is saying quite clearly that the time one becomes permitted to eat terumah is when the sun sets after he has immersed in a mikveh. This must be the time alluded to in the verse ובא השמש וטהר as the “coming of the sun”. If so, why does the Gemara need to solve its question from a Baraisa?
Tosfos offers an entirely different approach to the Gemara’s challenge: Perhaps the verse is speaking of the “coming of [the sun’s] light”? Tosfos holds that sunset consists of two events:
A) The sphere of the sun passing over the horizon, when it is still quite light. This is called ביאת אורו, the great source of light, the sphere of the sun, has gone below the western horizon and cannot be seen. At this time there is of course ample light still reaching us.
B) Approximately an hour later the sun is so far below the horizon that no light at all reaches us from the sun. This is called ביאת שמשו, the sun is giving us no light whatsoever.¹The description of the setting of the sphere of the sun with its great light as ביאת אורו and the absence of any light from the sun as ביאת שמשו seems a bit strange. See תוספות הרא"ש who cites the ערוך as explaining the Gemara’s question as Tosfos does, but reverses the meanings of ביאת שמשו and ביאת אורו.
It is this second sunset, which will soon be followed by the appearance of the stars that is the legal end of the calendar day.
To make this understandable, on the day of the vernal or autumnal equinox, March 21st or September 21st, the sun sets at six p.m. That is the first sunset A) ביאת אורו - the sphere of the sun has slipped below the western horizon. It is still quite light. The sky grows increasingly darker because the sphere of the sun continues to move further and further below the horizon. At about seven p.m. there is no longer any light reaching us from the sun. That is the second sunset B) ביאת שמשו, when no rays of the sun are reaching the sky.
The Baraisa clearly says that it is ביאת שמשו, sunset B) that must pass before the tamei can eat terumah. Thus, the translation of ובא השמש is sunset B). The query of the Gemara according to Tosfos is: Perhaps the Torah is speaking of sunset A), when the sphere of the sun passes over the horizon?
For the sake of clarity, I will divide the verse in both the Gemara’s conclusion and in the challenge. We can answer: That this is the explanation of the Gemara’s challenge. How do we know that
1) the verse ובא השמש - “and the sun will set and (X) become pure” is speaking about sunset B) when the sun is absolutely below the horizon and no light rays reach us, and
2) what is meant by וטהר - “it, the sky, becomes pure” - the entire day has passed, because there is absolutely no light reaching us from the sun?
Perhaps,
1) the words ובא השמש -the sun will come, mean the coming of its light (sunset A) which is at the beginning of sunset and that is when it first enters into the sky below the horizon, and there is still time in the day to travel five mil²See Pesachim 94a, where there is a dispute about the distance that one can travel between sunset A) and the appearance of the stars. There are those who say that the distance on can travel is five mil (each mil is between three and four thousand feet). Others hold that the distance is four mil. Tosfos here cited the first opinion mentioned in the Gemara. However, as far as halacha is concerned, we rule that the distance is four mil, which is seventy two minutes. Keep in mind that there are myriad opinions about sunset and the appearance of the stars. I have explained this Tosfos according to the opinion of Rabbeinu Tam, who is the Rishon of record in this issue of two sunsets. See תוספות הרא"ש who attributes this position to Rabbeinu Tam’s elder brother the רשב"ם. till the stars appear.
2) And what is meant by the word וטהר and he will become pure? The person will be purified from his tumah and he need not wait till the stars appear.
According to this explanation the idea that one is first permitted to eat terumah after offering sacrifices on the eighth day was never considered. The Gemara is wondering only why it is assumed that sunset B) that allows one to eat terumah and not sunset A). Now, there is no difficulty at all with the Mishna cited in He’arel, because the Gemara could say that when the Mishna there uses the term “the sun set in the west”, it means the setting of the sphere with its great light. We have absolutely no proof that the Mishna is speaking about the appearance of the stars as opposed to the sphere of the sun setting below the horizon. The term ‘the sun set in the west’ can apply equally to both sunset A) and sunset B).
In regard to the third difficulty, that the Gemara should have solved its question of whether the verse ובא השמש is referring to the setting of the sphere or to the setting of all light of the sun, it also cannot not be resolved from the Mishna in Negaim 14, 3, that [the verse] ובא השמש is speaking of (sunset B) and the appearance of the stars. The term used by the Mishna “the sun set in the west” can easily be interpreted as sunset A). There is no proof at all that one is required to wait until the stars appear.
It is for this reason that it was necessary here to cite the Baraisa that identifies the end of the day as when the stars appear. It is only from that Baraisa that we know that the Rabanan interpreted the verse ובא השמש as speaking about sunset B) and not sunset A).

I.e. the disappearance of the sun below the horizon, but not the appearance of the stars. So Tosafot ; Rashi, less probably, refers Lev, xxii. 7 to the dawn of the eighth day.