Commentaire de citation sur Néhémie 9:19

החודש הזה לכם ראש חדשים, the determination of the calendar, i.e. months of the year, is made only on the basis of astronomical calculations and is not based on visual observation. The proof that this is so is the fact that during the forty years the Israelites were wandering in the desert the heavenly cloud which enclosed them by day, shielding them from heat and from the eyes of curious outsiders, as well as the pillar of fire by night, made visual observation an impossibility. This is the meaning of the verse in Nechemyah 9,19 ואתה ברחמיך הרבים לא עזבתם במדבר את עמוד הענן לא סר מעליהם ביומם להנחותם בהדרך ואת העמוד האש בלילה להאיר להם ואת הדרך אשר ילכו בה. “You, in Your abundant compassion, did not abandon them in the wilderness. The pillar of cloud did not depart from them to lead them the way by day, nor the pillar of fire by night to give them light in the way they were to go.” How then were they possibly able to determine the times of the new moon and all the important elements of the calendar depending on this by visual observation? There is no question that the central commandment meant by our verse is to calculate the times of the new moon by astronomical means.

Rabbeinu Chananel also states clearly [Torah Shlemah by Rabbi M. Kasher pages 46-48] that we base our calendar on astronomical calculations rather than the sighting of the moon. For proof of this, consider the fact that during the Israelites’ wanderings in the desert for 40 years when their encampment was totally enveloped by the ענני הכבוד, G’d’s clouds of distinction, neither the people nor their leaders were able to sight the moon. They did not even see the sun by day either but depended totally on the pillar of cloud or fire to light the way for them. This is confirmed by Nechemyah 9,19: “You in Your abundant compassion did not abandon them in the wilderness. The pillar of cloud did not depart from them to lead them on the way by day, nor the pillar of fire by night to give them light. in the way where to go.” How would the Israelites have been able to fix the date of the new moon unless they had based themselves on their astronomical calculations? Clearly, the principal method of determining the new moon is based on calculations.