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The Great Z'manim Debate: The History, The Science, And The Lomdus
Someone who is not familiar with nature and has never pondered the daily path of the sun, the stars, and the moon cannot begin to appreciate the way Chazal and the Rishonim describe the path of the sun.
[This] sefer not only clarifies the sugya of z’manim in all of its details, but is an intellectual adventure to read. The narrative that unfolds is one of a quest that spans generations. It is the story of chachamim toiling in the pursuit of truth, striving to unravel confusing and conflicting sources in their search to establish the time of tzeis ha’kochavim and alos ha’shachar , as well as the proper z’manim for mitzvos . It is a quest that persists today, as there remain widely different practices in calculating z’manim. All of these practices are rooted in different opinions among the Torah giants that engaged in this pursuit of truth. It is the object of this sefer to illuminate the rationale for each of the various shitos rather than to pasken halachah l’maaseh.
[This] sefer not only clarifies the sugya of z’manim in all of its details, but is an intellectual adventure to read. The narrative that unfolds is one of a quest that spans generations. It is the story of chachamim toiling in the pursuit of truth, striving to unravel confusing and conflicting sources in their search to establish the time of tzeis ha’kochavim and alos ha’shachar , as well as the proper z’manim for mitzvos . It is a quest that persists today, as there remain widely different practices in calculating z’manim. All of these practices are rooted in different opinions among the Torah giants that engaged in this pursuit of truth. It is the object of this sefer to illuminate the rationale for each of the various shitos rather than to pasken halachah l’maaseh.
188 pages, Hardcover
Published September 22, 2022
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Displaying 1 - 3 of 3 reviews
November 9, 2023
If you go to the MyZmanim website and click on Extended Daily Zmanim, you will find close to 40 different times halachic categories during the day. The nature of time is engrained in the daily life of an observant Jew. To the degree that if you ask a person on the street what time sunset is, they might be able to guess within 45 minutes or so. Ask the average orthodox person what time sunset is, and they can likely tell you within a few minutes.
In The Great Z'manim Debate: The History, The Science, And The Lomdus (Mosaica Press), Rabbi Ahron Notis has written a fascinating and engaging read about the nature of time and how it’s dealt with in halacha.
One area the book deals with is the fluctuating length of bein hashemashos (twilight). He writes that when the Gemara sets a length for how long twilight is, they were referring to their locations in Bavel and Israel. Yet when trying to coordinate the length of time for twilight in other locals, they do not synchronize.
He quotes the Minchas Kohen who felt that the amount of time for bein hashemashos was indeed not the same everywhere. But was reluctant to say such a novel idea, even though he knew it was undeniably true.
In many communities, members of modern orthodox shuls may already be home checking their emails on a motzei shabbos, while those who daven in the Kollel are just starting mariv. In The Great Z'manim Debate, he shows you how in fact, the Kollel may be davening much later than necessary.
The overall issue is that the nature of zmanim is so engaged in our lives, that any innovation is treated with suspicion. Many of the ideas Rabbi Notis proposes may seem wild, but are, in fact, quite sound. Of course, it’s ideas like those that got Rabbi Slifkin thrown into cherem.
Rabbi Notis admits he doesn’t expect communities to change their davening times. But what the book shows is that it’s important to understand the underlying concepts around halachic time. Given that it impacts every minute of our lives.
In The Great Z'manim Debate: The History, The Science, And The Lomdus (Mosaica Press), Rabbi Ahron Notis has written a fascinating and engaging read about the nature of time and how it’s dealt with in halacha.
One area the book deals with is the fluctuating length of bein hashemashos (twilight). He writes that when the Gemara sets a length for how long twilight is, they were referring to their locations in Bavel and Israel. Yet when trying to coordinate the length of time for twilight in other locals, they do not synchronize.
He quotes the Minchas Kohen who felt that the amount of time for bein hashemashos was indeed not the same everywhere. But was reluctant to say such a novel idea, even though he knew it was undeniably true.
In many communities, members of modern orthodox shuls may already be home checking their emails on a motzei shabbos, while those who daven in the Kollel are just starting mariv. In The Great Z'manim Debate, he shows you how in fact, the Kollel may be davening much later than necessary.
The overall issue is that the nature of zmanim is so engaged in our lives, that any innovation is treated with suspicion. Many of the ideas Rabbi Notis proposes may seem wild, but are, in fact, quite sound. Of course, it’s ideas like those that got Rabbi Slifkin thrown into cherem.
Rabbi Notis admits he doesn’t expect communities to change their davening times. But what the book shows is that it’s important to understand the underlying concepts around halachic time. Given that it impacts every minute of our lives.
December 28, 2025
This is an amazing book for anyone who ever wanted to understand the subject of zmanim better.
The author just an incredible job at taking a very complicated subject and explaining it on a way that most will be able to understand.
He begins with the background about how the chazal and later the rishonim and achronim understood astronomy and explains it very well and based on that everything becomes much easier to understand.
I would highly recommend this to anyone that was ever interested in getting a foothold in this subject!
The author just an incredible job at taking a very complicated subject and explaining it on a way that most will be able to understand.
He begins with the background about how the chazal and later the rishonim and achronim understood astronomy and explains it very well and based on that everything becomes much easier to understand.
I would highly recommend this to anyone that was ever interested in getting a foothold in this subject!
January 10, 2024
The English-speaking world owes a great debt of gratitude to Rabbi Ahron Notis for researching and publishing this fantastic Sefer on Zmanim. It is a fascinating intersection of science, history, and Halacha, much of which has been previously inaccessible (or, very difficult to access) to the average person (like myself). It is probably the most interesting book I have ever read on science and Halacha. While it is not a long book (less than 200 pages), each chapter - even each page - is densely packed with incredible information on how Zmanim were calculated historically, where and how previous scholars went wrong, and how our understanding of science helped clarify matters with time. Part I, on astronomy, contains a lucid description of the cycle of the sun and stars, and how they relate to Halachic times, in my opinion worth the price of the book alone. The next two parts go through the Gemaras, Rishonim, and Achronim that discuss these Zmanim, and concludes with practical Halachic Zmanim that naturally emerge from the understanding gained in the earlier parts of the book. I enjoyed the book so much that as soon as I finished it, I immediately started reading it again. I have already recommended it to many people, and will undoubtedly be referencing it on a regular basis in the future. Thank you Rabbi Notis!
Displaying 1 - 3 of 3 reviews