The Halachic Dateline in Given Extensive Treatment in 3-Volume Set of Books

Crossing the Dateline [3 Volumes] by Rabbi Mordechai Kuber (Mosaica Press, 2020)

Crossing the Dateline [3 Volumes] by Rabbi Mordechai Kuber (Mosaica Press,


Reviewed by: Rabbi Reuven Chaim Klein

In this monumental work, Rabbi Mordechai Kuber gives the topic of the Halachic dateline the extensive and sophisticated treatment that it deserves. He holds the reader’s hand through this intricate topic and puts down the complex discussion into plain English. Throughout this book’s three volumes, the reader constantly feels like Rabbi Kuber is talking directly to him (his subtle humor is even there, if you look hard enough for it). In a nutshell, this book discusses if and where the Halachic dateline that divides the world might lie, and what the different Halachic ramifications of crossing that dateline might be.

In general, repetitiveness in a work of writing is not usually considered good form, but in a complicated work like this, Rabbi Kuber skillfully uses repetitiveness to make sure the reader is still following along as his discussion becoming increasingly more complex. This work is not as meticulous in citing its exact sources as one might expect of a master educator like Rabbi Kuber, but this was probably done deliberately to keep the focus on the ideas/arguments proffered, rather than on the rabbinic personalities who took those positions.

Throughout his work—and particularly in Volume I—Rabbi Kuber goes out of his way to explain, and even justify opinions with which he himself clearly disagrees. This act of integrity demonstrates true intellectual honesty on Rabbi Kuber’s part, and is somewhat of a departure of the more polemical nature of other works written on this controversial topic.

The first volume of Rabbi Kuber’s trilogy offers an overview of the historical circumstances that first led to the question of where in the world to place the Halachic dateline. He surveys the various opinions and gives the requisite background information in terms of how the Halachic process works and what the relevant sources say. Rabbi Kuber then carefully considers how a person should treat such places as Japan, Australia, New Zealand, Alaska, and Hawaii. When all is said and done, this reviewer counted more than ten different opinions on where the Halachic dateline ought to be placed—all of which are thoroughly considered in this volume of Rabbi Kuber’s work. Although the nature of this analysis sometimes borders on the technical and tedious, it remains a gratifying read and an intellectually stimulating study.

A large chunk of this volume is dedicated to elucidating various ways of explaining a somewhat obscure Talmudic passage concerning the sanctification of the new moon. The explanations of the different commentators to that passage bear direct relevance to the question of the Halachic dateline and where it ought to be. Rabbi Kuber also presents a fairly lengthy chapter on the opinion of the Radvaz, who would seem to reject the notion of a Halachic dateline entirely and instead endorses a “personalized” way of determining the day of the week when in doubt.

In Volume II of his work, Rabbi Kuber brackets out talk of where the Halachic dateline might be, and focuses on the practical ramifications of its existence. He begins with a lengthy study on the Halachic consequences of crossing the dateline to or from a zone in which it is either Shabbos or a holiday. In practice, this can happen if one is vacationing on a cruise that crosses certain parts of the Pacific Ocean or travels in an airplane across the Pacific. Rabbi Kuber discusses which commandments/prohibitions of those sacred times must be observed and how to observe them.

In this volume, Rabbi Kuber considers such questions as whether Shabbos can start or end in the middle of a day (instead of at sunset) for such a traveler, and what prayers must be repeated if experiencing a given calendar day twice.

Rabbi Kuber offers practical guidance about eating (e.g., if/when one should recite Kiddush/Havdalah when crossing the dateline, under what circumstances is a traveler obligated to break bread on two loaves, and in what cases is there an obligation to eat three meals on Shabbos) and fasting when travelling from one day to another. This volume also explains how travelling across the dateline in either direction might affect one’s observance of Purim and Chanukah, as well as Hilchos Niddah. That said, the most relevant discussion in this volume centers on one’s obligations to pray and how crossing the dateline into tomorrow or yesterday might affect those obligations.

This volume ends with a 50-page quick reference guide (including charts) that summarizes the relevant Halachos for one crossing the dateline. This reviewer suggests that the summaries and quick reference sections of Rabbi Kuber’s multi-volume work ought to be published as a stand-alone “idiot’s guide” to the topic, without needing to get into all of the intricate Halachic analysis that drove Rabbi Kuber to the conclusions he makes.

The third volume of Rabbi Kuber’s magnum opus divides into two parts. In the first part, Rabbi Kuber returns to the question of where the Halachic dateline ought to be that he discussed in Volume I and uses the uncertainties discussed there to paint a picture of how that question bears on the issues discussed in Volume II. Using time-tested Halachic principles like being stringent with Biblical prohibitions and lenient with Rabbinic prohibitions, this volume offers practical guidelines for dealing with the various Halachic uncertainties concerning prayers, Shabbos/holiday observance, Sefiras HaOmer, and more. One interesting point that comes up multiple times in this discussion is that an individual’s day of the week might not necessarily line up with his or her day of the month.

The third volume then presents several essays on topics that are somewhat tangential to the book’s core discussion, but which remain nonetheless related. These discussions are of a more scientific/technical nature, and discuss things like the time of the molad (new moon) and bein ha’shmashos (twilight), as well as Halachic guidance for someone flying above the arctic circle and an astronaut in outer space. This last volume is rounded off with a glossary of terms in Hebrew/Aramaic/Yiddish that appear in the book, a bibliography of the works cited, and short biographical sketches of all the authorities invoked.

As with the previous two volumes, a user-friendly index at the end of this volume helps tame the unwieldly behemoth.

Rabbi Kuber’s vast knowledge and experience in the field of Halacha certainly qualifies him to offer his learned opinion on even the most complex topics—and he does not shy away from doing so. Yet, his personal humility and transparency shine through from his analysis and conclusions.

This wonderful book touches on all sorts of fields. Obviously, Rabbi Kuber’s discussions heavily draw on geography (using customized Google Maps to reify the discussions), but also in engage in theoretical/practical Halacha, the philosophy of Halacha, some Lomdus, some astronomy, some mathematics, and even some history (see his discussions of Ptolemy’s map of the inhabited world). If you enjoy such intellectual compilations and want to wet your feet in those topics, then this book is for you. If you were ever interested in the topic of the Halachic dateline but did not know where to start, then this book is for you. And certainly, if you ever travel to the area between California and China, then this book is a must-have.


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