Explanation: Why do we extend Elul, as it would be better that they should not extend it and that there would not be two days due to this doubt!

Text: Rabeinu Tam does not have the text, "from before it." If Rosh Hashanah and Sukos would be before it, we should say the reason is because of a dead person since Yom Kippur would fall on Sunday!

Observation: This is not Rebbi Yehudah Nesiah who permitted oil of Nochrim in Avodah Zarah (36a) and who lived during the time of Rav and Shmuel, as he was the son of Rabban Gamliel who was the son of Rebbi Yehudah ha'Nasi. The Rebbi Yehudah Nesiah here is the student of Rebbi Yochanan who was under the authority of Rav and Shmuel.

Explanation #1: Rashi explains that this only applies to Nisan and Tishrei as the holidays are dependent on them, but not to the other months.

Explanation #2: Some give the opposite explanation (that it only applies to the other months, not Nisan and Tishrei).

Observation: In Erchin (9b), the Gemara asks, "Isn't there an additional day every thirty years?" This is because every year has an extra four days, eight hours, and eight hundred and seventy six parts, and those parts end up adding up to one day every thirty years. The Gemara answers, "Since it is not pertinent every year, it is not counted."

Explanation: The law that we threaten witnesses to testify at the time the moon is supposed to be seen that they saw the moon, even though they didn't, is when the thirtieth night and day are from the new month (and the old moon does not appear on that night and day).

Explanation #1: Rashi explains that he saw in the Yesod of Rebbi Sa'adyah that the moon will always be in the southeast corner of the sky before it becomes a new moon, and after it becomes a new moon it will go to the southwest corner. When it is in the east, it is seen by the people in the east and not to those in the west, and when it is in the west it is seen by the people in the west and not to those in the east.

Explanation #1 (cont.): This is why the old moon does not appear to be covered to the people of Babylon in the east until six hours into the day, while to the people in Eretz Yisrael who are further away it appears to be covered eighteen hours into the day. The new moon does not appear to be covered to the people of Eretz Yisrael in the west until six hours into the day, while to the people in Babylon who are further away it appears to be covered eighteen hours into the day.

Explanation #1 (cont.): According to the opinion who derives from Yom Kippur the day goes after the beginning of the night, and if the old moon is seen at the beginning of the night one may not be Mekadesh the Chodesh during the following day. According to the opinion that we derive from Pesach we do not worry about this, rather we only ascertain that the old moon has not been seen from after Chatzos that night. (This is why the Gemara says the difference is Chatzos at night.)

Observation: Rashi seems to imply that we do not establish the month based on the people of Babylon, but rather it is based on the people of Eretz Yisrael. Despite the fact that the people of Babylon saw the old moon at night, the people of Eretz Yisrael may be Mekadesh the month the next day. We do not take into account that the people of Babylon saw the moon. The people of Babylon themselves establish Yom Kippur and all of the festivals based on the day that the people of Eretz Yisrael saw the new moon, even though the people of Babylon saw the old moon that night (and therefore would not be able to be Mekadesh the new month the next day).

Question #1: This is difficult. How do we know that the Pasuk is Makpid regarding when the people in Eretz Yisrael see the moon, and not when the people in Babylon see the moon?

Question #2: Additionally, when the moon starts getting less full, it will not be seen in the beginning of the night until it becomes a new moon. The way it was established (by Hash-m) is when the new moon comes out it comes out during the day and is seen at the beginning of the night for a small amount of time, and then it disappears. The next night it stays out for a little longer, and it keeps staying out longer until it becomes full.

Question #2 (cont.): It then (when it is full) goes out at the beginning of the night and it shines the entire night until daybreak, and it sets after the morning light. It then starts lessening itself every night, and it stops coming out early in the night, and it starts to come out later every day until the end of the month. Whatever it takes away from when it comes out at night it adds to when it is seem during the day, whether at the beginning or end of the month.

Explanation #2: It is more reasonable to explain that the case here is regarding the new moon. The night and day must be a time when the new moon appears, meaning that the new moon will appear on the twenty ninth of Adar before the night of the thirtieth of Adar, in order to ensure that the entire thirtieth of Adar both day and night are included in the time of the new moon.

Observation: However, this is not the custom, as we do not invalidate an "old Molad" (from establishing Rosh Chodesh when it is seen) unless it is after the eighteenth hour.

Explanation #3: Some say, "the night and day must be from the new moon" means that the way Beis Din is Mekadesh the moon is only after a night and day, not after a day and night.

Explanation #3 (cont.): If the new moon appeared during the day before Chatzos and Beis Din were Mekadesh the month, the night before it is deemed Rosh Chodesh. If the new moon was seen after Chatzos and it was not seen during the day the month is only considered Rosh Chodesh starting from the next day, not the previous day. This is the intent of the statement of the father of Rebbi Simlai.

Question: According to this explanation the answer, "Chatzos at night is the difference between them" is difficult, as there is no opinion that Yom Tov and Rosh Chodesh should not start from the nighttime.