When the Syrian-Greeks - in the time of Chanukah - wanted to undermine and eventually destroy Jewish life, one of the three commandments they tried to abolish was the proclamation of Rosh Chodesh. They knew that without a calendar as ordained by the Torah, the festivals could not be observed and major components of Jewish life would come to a standstill. Today, there is no Sanhedrin, no means of establishing Rosh Chodesh according to sightings of the new moon. How is our present-day calendar designed? What are its complex computations? Why can't Rosh Hashanah fall out on Sunday, Wednesday, or Friday? How are the leap years determined, and how is it that the solar years and lunar years are kept in equilibrium? These are only a few of the many problems that are analyzed and clarified in this brilliant presentation by HaGaon Harav David Feinstein, Rosh Yeshivah of Mesivtha Tifereth Jerusalem, and one of the world's great poskim.

There is much more in this stellar book. It presents the Rosh Yeshivah's insights into all the special days of the Jewish calendar, explanations of their laws, and reasons for many of our familiar but sometimes mysterious customs.