The Sanhedrin Sanctification
The following is a brief description of the procedure the Sanhedrin followed in days of yore to determine the date of the onset of a new month. On the 30th day of every month, the Sanhedrin would "open for business" in a large courtyard in Jerusalem called Beit Ya'azek. Witnesses who claimed to have seen the new moon on the previous night would come to give their testimony and be cross-examined.
The members of the Sanhedrin were well schooled in astronomy. They knew exactly when the new moon would have appeared, and where it would have been visible. Nevertheless, the sanctification of the moon depends on the crescent new moon actually being seen by two witnesses. The word "this" (in the above-quoted verse, "This month shall be to you...") implies something that is actually seen.
The rabbis of the Sanhedrin would question the witnesses in the order of their arrival. They knew what the proper responses to their questions ought to be, and were thus quickly able to identify fraudulent claims. Starting with the elder of each pair, they would ask: "Tell us how you saw the moon:
- In which direction was it in relation to the sun?
- Was it to the north or south?
- How high in the sky did the moon appear to be?
- In which direction were the crescent's tips facing?
- How wide was it?
After they had finished questioning the first witness, they would bring in his partner and question him in similar fashion. If the two accounts corroborated, the evidence was accepted.
That day, the thirtieth day, was now declared Rosh Chodesh of the new month. The head of the Sanhedrin would proclaim: "Mekudash!" ("Sanctified!") and everyone would respond, "Mekudash! Mekudash!" The previous month was now retroactively determined to have had only twenty-nine days.