New Moon dilemmas
החדש הזה לכם ראש חדשים ראשון הוא לכם לחדשי השנה
This month shall be for you the beginning of the months. It is the first for you for the months of the year
Our Sages learn from this verse the mitzvah of Sanctifying the New Moon. Unlike our current calendar, which is fixed, the Jewish months originally weren’t set in stone. For the new month to begin, two witnesses had to declare in a Jewish Court that they had seen the Moon after the New Moon occurred. Three judges would interrogate the witnesses, and after confirming that they weren’t mistaken, the judges would declare the month sanctified, and the new month would begin.
When Moshe was first introduced to this mitzvah, we are told that he had difficulty understanding it. He wasn’t sure what the Moon was supposed to look like when this mitzvah was to be performed, so Hashem showed him a vision of the Moon. What was so difficult to understand? When the New Moon occurs, the Moon is invisible. Approximately eighteen hours later a sliver of the moon becomes visible. What’s so complicated?
Another question is based on a Midrash. The first time the New Moon was sanctified was at this moment, when Hashem introduced the mitzvah. Hashem, Moshe, and Aharon formed the Jewish Court to sanctify the Moon, and the ministering Angels were the witnesses. The problem is, we are taught that if the Court itself sees the New Moon, there’s no need for witnesses. Seeing is obviously more reliable than hearing. Why then did the ministering Angels need to testify? As we said, Hashem showed Moshe and Aharon the Moon.
We can find one answer to both of these questions. We can suggest that the entire concept of Sanctifying the New Moon depends on the Land of Israel. Since Egypt is southwest of the Land of Israel, and since the Sun moves from East to West, the sun sets in the Land of Israel before Egypt by some small amount of time. That means that while it was still day in Egypt, it was then night in the Land of Israel. There, the Moon was easily detectable. The ministering Angels were therefore able to witness the Moon in the Land of Israel, and testify that to the Jewish Court comprised of Hashem, Moshe, and Aharon in Egypt.
To help with the sanctification, Moshe had to verify that what the Angels saw was actually the Moon. By the time the Moon was visible in Egypt, it was already a little bigger than it was when they Angels saw it in the Land of Israel. Moshe had to calculate based on the degree difference in latitude and longitude what the Moon would have looked like earlier in the Land of Israel. Without this calculation, he wouldn’t be able to properly interrogate the Angels to confirm what they saw. Since it was so difficult, Hashem showed Moshe a vision of what it looked like over there, at the time. With this, we have answered all the questions.
 Based on Chasam Sofer Al HaTorah to Exodus 12:2
 Exodus loc. cit.
 See maseches Rosh Hashanah, which deals extensively with this mitzvah
 Rashi ad. loc., quoting Mechilta ad. loc.
 Brought in one of the piyutim for Parshas HaChodesh s.v. אבי כל חוזה
 Rosh Hashanah 25b
 The Chasam Sofer asks a third question: Since this episode occurred at bein hashmashos, twilight, due to the fact that Hashem only spoke to Moshe by day, yet it had to be late enough to see the Moon (Rashi loc. cit., quoting Mechilta loc. cit.), this creates a problem. If it was the end of the day, and the Moon they were seeing was really that of the second of the month, that means by the time they sanctified the month, the whole first day of the month had already elapsed. That would diminish from the time they needed to properly prepare for Pesach. They were supposed to be told on the first of the month to start preparing, but by the time Moshe would go tell them, it would be the second of Nissan (see Rashi to v. 3). And if we say that it was really the beginning of the next day, making that night the first of the month, then that means Hashem spoke to Moshe at night, which we were told He doesn’t do. Either way it’s a problem. I believe this was the Chasam Sofer’s intent, even though he wrote בצרי ליה ב’ שבתות דשואלין ודורשין. Initially I wasn’t sure what he meant, as I thought that concept refers to the thirty days of preparation before Pesach, not two weeks (Pesachim 6a). Indeed, that is how we rule (Shulchan Aruch Orach Chaim 429:1). However, I found in Sha’ar Yosef ad. loc., he brings another version of the Chasam Sofer: ובצר ליה יום א’ מב’ שבתות דר”ג. Indeed, we see Rabban Gamliel in Pesachim loc. cit. says two weeks, which is how Rashi cited above seems to explain the verse. I suppose that’s why he picked Rabban Gamliel’s opinion
 This means that Hashem spoke to Moshe while it was still day, even though they were sanctifying the New Moon of the “next night”
 The Chasam Sofer as we have it doesn’t say this, but the Sha’ar Yosef loc. cit. in the alternate version of the Chasam Sofer seems to say this