The fascinating story of time. When did man first become conscious of time? What is the origin of the calendar? How did timepieces evolve? Who developed the 24 hour day, the 60 minute hour? Why Meridians and longitudes? These and many other questions about the complicated subject of time and its measurement are raised and answered by author-scientist Isaac Asimov. He tells how man established Day 1 as January 1,4713 B.C., why the week has 7 days, why there is Leap Year. He discusses the Gregorian calendar and the Julian calendar; why the lunar year does not match the seasons; and mankind's troubles in coordinating the phases of the moon with planting time and harvest time.