The Rogatchover Gaon (cited in Mefaaneach Tzefunos p. 195 http://www.hebrewbooks.org/pdfpager.aspx?req=7039&st=&pgnum=200&hilite=) proved from Tosfos that one may eat Seudas Shabbos in star light.
Where is this coming from ? Which gemara? logic?
Reb Chaim, this is a tough question!
a. I have not yet found what the Rogatchover is referring to from Eruvin 38. I assume he means Tosfos on 38b DH v'Ha, who is discussing the Se'udah ha'Re'uyah -- the requirement that the Eruv be fit before Shabbos as a Shabbos meal. However, there is no mention there of stars, so I still have not yet figured it out. I should point out that the Rogatchover does not write explicitly that he is citing Tosfos; rather, he refers to the Ri. Even though the Ri is often cited by Tosfos, it is possible that in this case the Ri is cited elsewhere by the Rishonim, not actually by Tosfos.
b. I will attempt to point out some other sources that the Rogatchover mentions. He mentions the Mordechai in Pesachim 101a, who comments on the Gemara there in which Abaye said that when he learned at the Yeshiva of "Mar" (a reference to Rabah), Rabah would make Kidush for them and tell them to eat something after the Kidush, because by the time they would get home there might be no candle alight there. The Mordechai writes that we learns from here that a candle is required for Kidush but it is not required for the Shabbos meal. This would be a support for the Ri, cited by the Rogatchover, that it is sufficient to have star light for the Shabbos meal, and one does not require candle light.
c. The Rogatchover also cites the Gemara in Berachos 53a. The Gemara there discusses what sort of candle one needs for Havdalah. The Gemara says that one may make Havdalah on the candle of a synagogue, but it depends on other factors. If there is a warden there, one may make Havdalah on the candle because the candle is there for him to eat using its light. However, if there is moonlight, we say that the Shamash could eat without the candle and it must be that the candle was lit only for the honor of the Shechinah present in the synagogue, and one may not make Havdalah on it because the rule is
that one may make Havdalah only on a candle whose light is actully needed.
Again, we learn from this Gemara that the Shamash can eat his meal without a candle if there is moonlight. This is another proof for what the Ri says, that one may eat Se'udas Shabbos in starlight.
These are all just initial thoughts. I cannot yet claim that I have arrived at the bottom of what the Rogatchover writes. One always must work hard to understand even a little of what the Rogatchover writes, and I hope to continue later, b'Ezras Hash-m.
a. It suddenly dawned on me that when the Rogatchover writes mentions the "Ri," he is referring to Rabeinu Yehonasan, on the Rif in Eruvin. This is on page 9b in the pages of the Rif. In DH u'Mistacher, he writes that he takes his bread with him and he eats his Shabbos meal to the light of the stars.
b. Now that we have found that the source is Rabeinu Yehonasan, let us understand more what the Rogatchover is saying. It seems to me that he is coming to explain the Din of the Gemara in Shabbos 25b that it is obligatory to light a candle for Shabbos. The Rambam (Hilchos Shabbos 30:5) writes that one's candle should be lit and his table should be set. The Rogatchover now has a Chakirah: Do we say that the candle requires a meal, or do we say that the meal requires a candle?
In other words, we know that one must light a candle on Friday night. Does that mean that one cannot eat the Shabbos Se'udah without a candle? The Rogatchover proves from Rabeiu Yehonasan in Eruvin 38 that one may eat the Shabbos meal even by starlight. This must mean that one must light a candle on Friday night, and this candle should be placed at the place where the Se'udah is being eaten, but if one is unable to do that, he may fulfill the Mitzvah of eating a Shabbos Se'udah even where there is no candle.
c. The Rogactchover then proves from Berachos 53a that the guardian of the synagogue may eat his meal by moonlight, as we mentioned above. This proves that the candle on Friday night should be lit at the meal, but nevertheless one may eat the meal without the candle if one has the light of the moon or the stars.
d. The Rogatchover then cites Tosfos in Pesachim 101a, DH uv'Kidusha, whose words show that one cannot fulfill the Mitzvah of Shabbos Se'udah withiut a candle. This clearly does not agree with Rabeinu Yehonasan. However, the Rogatchover then cites the Mordechai that I mentioned above, who says that one may eat the Se'udah without the candle. This clearly does not agree with Tosfos and is a support for Rabeinu Yehonasan.
This is a beautiful piece in the Rogatchover!
Now that we have seen the Rogatchover in full and explained what his sources are, I think it is worthwhile explaining why it is not at all obvious that everyone would agree with what the Rogatchover writes, and that there are quite a few Chidushim lying among his tersely-phrased words.
1) Firstm it is very important to know that this whole piece of the Rogatchover runs contrary to the views of Rashi and Tosfos! I am referring to Rashi and Tosfos to Shabbos 25b that I cited briefly in my reply above. Abaye there states that lighting a candle on Shabbos is obligatory. Rashi explains that no important meal is eaten without light similar to daylight. Rashi clearly does not agree with Rabeinu Yehonasan cited by the Rogatchover that one may eat the Shabbos Se'udah by starlight.
2) Tosfos there (Shabbos 25b, DH Hadlakas) writes that the Gemara means that it is obligatory to eat the Shabbos Se'udah where a candle is present. Again, this is in contrary to the view of Rabeinu Yehonasan that the stars are sufficient. However, now that we know what Rabeinu Yehonasan wrote, we can notice that what Rashi and Tosfos write is not actually stated explicitly in the Gemara. The Gemara states merely that lighting a candle is a Chovah, but it was only Rashi and Tosfos who linked this with the Shabbos meal. Rabeinu Yehonasan disagrees and maintains that there is not necessarily a connection between the meal and the candle.
3) Why is it that the Rogatchover keeps the opinions of Rashi and Tosfos hidden from us? I suggest that this is because the Rambam did not write explicilty what his opinion is on this matter. I read once that the Rogatchover used to call the Rambam "the Rebbi." If the Rambam did not say anything against what he was writing, then the Rogatchover did not feel obligated to conform with other Rishonim. When the Rambam cited the Gemara in Shabbos 25b in Hilchos Shabbos 5:1, he did not connect at all the Shabbos candle to the Shabbos Se'udah. In 30:5 he wrote that there should be a candle lit and a table set, and that this is included in the honor of Shabbos. However, he did not write explicitly that the meal must be to the light of the candle. This may be why the Rogatchover felt free to omit the opinions of Rashi and Tosfos (in fact, at the end he does cite Tosfos in Pesachim 101am DH uv'Kidusha, who says that one must not eat the meal without the candlem but then he immediately cites the Mordechai who disagrees with Tosfos, as I wrote earlier).
I hope we have seen a little better the context within which the Rogatchover needs to be understood.