Books by Fred Reiss
~Jewish Calendar~
~Kabbalah and Jewish Mysticism~
~Jewish Religious Fiction~
~History of Education in Camden, NJ~
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 The Jewish Calendar: History and
Inner Workings

"Reiss raises many interesting questions.... You will find the answers quite illuminating and informative." Rabbi Michael L. Samuel, San Diego Jewish World.

Chapter 1 describes the precursors to the Jewish calendar, particularly those developed in Mesopotamia, Egypt, Greece, and Rome, showing their similarity and differences and how each might have influenced the Jewish calendar.

The observational Jewish calendar is the original Jewish calendar. Months begin with seeing the first very-thin crescent of the New Moon and the seasons are regulated by the sun, making the Jewish calendar a lunisolar calendar. In Chapter 2, the history of its development is offered, starting in biblical times and into the First and Second Temple periods, followed by the mathematical advances occurring in the Talmudic Era.

Chapter 3, entitled The Calculated Jewish Calendar: Measurement of Time, examines and explains the definitions and mathematical constants and associations among the units of civil and Jewish time, such as the chelek and regah with the minute and second, whose meanings are needed for understanding the computed calendar. The molad, the time of lunation, when the New Moon inaugurates the new month, is the most important feature of the calculated Jewish calendar and is introduced in Chapter 4, together with its initial value, known as the Epoch Molad. The chapter carefully takes the reader though several methods of computing the molad for any a given year.

The New Moon of the month of Tishri, the first day of Rosh Hashanah, the Jewish New Year, is different from all other New Moons because the rabbis established four rules that can, and most often do, delay the start of the New Year. Chapter 5 presents the postponement rules and delivers an in-depth description of each. There is an analysis of the effect of the rules on such things as the limits on which days of the week Rosh Hashanah can arise in consecutive years and the character of the year, which mandates the days of the week on which holidays can start, and the parasha of the week, read in synagogues worldwide. The chapter also examines molad intervals and how they distinguish between the various lengths of the Jewish year.

All calendars have cycles and recursive periods. Chapter 6 compares and contrasts the cycles and recursive periods between the Jewish and civil calendars. The nineteen-year cycle is discussed in detail, including its various lengths and starting days of the week. Numerous examples are offered, giving the reader shortcuts for finding the molad for any year from the Epoch Molad, or from any known molad using cycles of years. In addition, the chapter shows the molad’s effect on the day of the week on which Rosh Hashanah begins. The chapter ends with a technique for computing any of the Jewish calendar’s sixty-one unique cycles and explains why other cycles found in the literature are spurious.

The Jewish calendar, like the civil calendar, works in cycles, the most prominent of which is the nineteen-year cycle, dictating when common and leap years occur. These cycles are aperiodic, they lack a discernible pattern of appearing, repeating, disappearing, and reappearing. Chapter 7, devoted to exploring the elusiveness of nineteen-year cycles, describes methods predicting how often and under what conditions cycles appear, vanish, and reemerge, as well as examines the most general rule regulating nineteen-year cycles, a rule which I call Nachshon’s Rule Four. Buried deep within the Jewish calendar are three supercycles. Chapter 7 also explains the rules guiding their operation.

Jewish calendar statistics, the theme of Chapter 8, describes recurrence data of various Jewish calendar events, such as: How often does a molad repeat? What is the distribution of the six possible lengths of the Jewish year? How frequently do each of the fourteen characters of the year appear? Do the four days on which Rosh Hashanah can fall appear equally? How often is Rosh Hashanah delayed by each of the four postponement rules?

The Gregorian calendar, our present civil calendar, has errors with respect to the motion of the sun. The Jewish calendar, being tied to the Gregorian calendar, has the same errors, but it also has errors with respect to the moon. Chapter 9 explains those errors and their meaning, as well as describes proposed remedies to mitigate them.

The question of whether or not Passover will fall in the “spring month” is a source of angst among Jewish calendar makers. No Jewish calendar is complete without determining T’kufah Nisan, the vernal equinox. The rabbis employ two methods for finding this important date, one by Mar Samuel and the other by Rabbi Ada, both are explained in detail in Chapter 10.

The first edition of The Jewish Calendar: History and Inner Workings copiously explained how to create a Jewish calendar for any year. The second edition, in Chapter 11, enhances calendar creation by elucidating how to find the civil date for any Jewish date and vice versa, allowing the reader to produce corresponding civil and Jewish calendars.

Although calendar computation is based on simple arithmetic, the methods can be long and cumbersome. The Jewish Calendar: History and Inner Workings, Second Edition, has additional appendices to help the reader carry out the computations and develop calendars more easily, including detailed versions of the fourteen types of Jewish calendars, cycle-equivalent values from one to one thousand, and comprehensive charts showing the recurrence of the sixty-one cycles, the cycles driving the entire Jewish calendar.

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