This fascinating book draws together a wealth of diverse material on the much-trusted (and rarely disputed) phenomenon we know as the calendar. From the fundamentals of astronomy to the world's ancient time-keeping schemes, to the development of the modern-day calendar, to the precise calculation of when specific dates occur (as in how one arrives at the date for Easter Sunday), this is a skillful yet approachable discussion of the calendar from both the historical and contemporary perspectives. Readers will even learn how to perform experiments and calculations for themselves by using such basic techniques as stargazing and simple mathematics.