Dates on the calendar have a problem that I have mentioned before. The reason is there does not seem to be any evidence that the calendar was in place during the period of the geonim. There are letters from the early geonim that have dates that do not correspond the the regular calendar that is in use.
So to say it was established by Hillel II is false. The earliest record of the calendar is from the time of the later geonim. So it is impossible that Hillel II sanctified all future new moons. And there is no Gemara which even hints to such an event.
The logical thing to do is simply count the day of the מולד the conjunction as the day of the new moon. That is at least what Tosphot says in Sanhedrin page 10 side b. But you could make a case for the Molad to be the actual date of the new moon from the actual people mentioned in the Gemara over there like R. Elazar who holds if the court sanctifies the new moon on time fine, but if not then anyway they sanctify it from heaven. Also from Rava and Rav Ashi you could make good case in this direction. But what seems to be the most compelling about this is that there is nothing else to go by. There is no other calendar,- since the present day one was adopted under false pretenses.
The main reason why this is serious is things like Passover when the issue of leaven bread is about as serious as it gets. When most people are still eating leavened bread, it is already 15 days after the Molad.
So to say it was established by Hillel II is false. The earliest record of the calendar is from the time of the later geonim. So it is impossible that Hillel II sanctified all future new moons. And there is no Gemara which even hints to such an event.
The logical thing to do is simply count the day of the מולד the conjunction as the day of the new moon. That is at least what Tosphot says in Sanhedrin page 10 side b. But you could make a case for the Molad to be the actual date of the new moon from the actual people mentioned in the Gemara over there like R. Elazar who holds if the court sanctifies the new moon on time fine, but if not then anyway they sanctify it from heaven. Also from Rava and Rav Ashi you could make good case in this direction. But what seems to be the most compelling about this is that there is nothing else to go by. There is no other calendar,- since the present day one was adopted under false pretenses.
The main reason why this is serious is things like Passover when the issue of leaven bread is about as serious as it gets. When most people are still eating leavened bread, it is already 15 days after the Molad.
