The new moon interval NA and the beginning of the Babylonian month

This study examines Babylonian records of the new moon interval NA (sunset to moonset on the day of first lunar visibility) and the connection of this interval to the length of the moon. I show that the NA intervals in the Normal Star Almanacs were computed using the goal-year method and were then used in turn to predict the lengths of each month of the year. I further argue that these predicted month lengths, adjusted occasionally on the basis of observation in cases where the moon’s visibility was considered marginal, formed the basis of the Late Babylonian calendar.