1,243. Acceptable and Unacceptable Testimonies

Hilchos Kiddush HaChodesh 2:5

If the witnesses say that they saw the moon’s reflection in the water, or they saw the moon behind the clouds or in a mirror, their words are of no significance and the month cannot be sanctified based on what they saw. The same is true if they saw part of the moon in the sky and the other part behind the clouds, in the water or in a mirror. If one says he saw the moon two stories high and another says he saw it three stories high, their testimonies may be combined (because this is not such a great difference). If one says that the moon was about three stories high and the other says that it was about five stories high, their testimonies may not be combined (because the discrepancy is too great to reconcile) but either of them may be combined with another witness who gave similar testimony, or whose testimony involved a discrepancy of only one floor.

Hilchos Kiddush HaChodesh 2:6

If witnesses say that they saw the moon without paying attention and later they tried unsuccessfully to see the moon so that they could testify, it is not a valid testimony and the new month cannot be sanctified based on it. Maybe they saw a gathering of clouds that resembled the moon and subsequently dissipated. If witnesses say they saw the moon on the 29th day, in the morning, in the east before sunrise, and later, in the evening, they saw it in the west on the 30th night, their testimony is believed and the new month can be sanctified because they did see the moon in its proper time; the testimony about what they saw in the morning is irrelevant. We disregard what they say they saw in the morning because that was obviously only a gathering of clouds that resembled the moon to them. Similarly, if witnesses testify that they saw the moon at its proper time but not on the 31st night, their testimony is believed because only what they saw on the 30th night is relevant.