ABSTRACT
The calendars have developed in reaction to each other. While they have in common the seven-day week, each has staked out its own weekly holy day. Each has a characteristic way of timing annual periods of penitence and celebration. Each has a characteristic way of maintaining solar and lunar cycles through calculation or observation. Efforts to follow or replicate astronomical cycles in distinctive ways have combined scientific challenge with religious quests. Only in this way can we explain the calendar controversies that have exercised some of the finest minds of their faiths.
