📋 Shiur Overview
Summary of the Learning Session: Rambam Hilchos Kiddush HaChodesh — Chapters 11–14 (Introduction and Foundations)
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A. General Introduction to the Calculations of Kiddush HaChodesh (Chapters 11–14)
1. The Foundation: Everything Revolves Around the World — Measured According to the Constellations
Words of the Rambam: The sun, moon, and all stars revolve around the world. The sun returns to the same place in the galgal hamazalos (zodiac) after a year’s time.
Explanation: The galgal hamazalos is 360 degrees. When we say the sun revolves once a year, we mean it returns to the same place in the galgal hamazalos.
Novel Points:
– The “same place” means not relative to north-south, but relative to the constellations — i.e., we measure where the sun stands in comparison to the constellations (mazal Tishrei, etc.). This is the basis of all calculations. An opinion that we measure according to north-south is explicitly rejected — “We see nothing regarding north-south, everything is about the constellations.”
– The mazalos are not a “fancy” wisdom — everyone could see the mazalos with the naked eye, and this is the basis of how we knew a year had passed.
– The mazalos are considered fixed and permanent for the calculation — they only move once a day (with the daily rotation), but not further in their own position. The Rambam already knew that the mazalos themselves also move (precession), but it takes very long (he mentions several tens of thousands of years), and therefore it’s not relevant for the calculation. Therefore, today the mazalos are not in the same place as their names (i.e., mazal Shor is no longer where the constellation Taurus is).
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2. The Sun and Moon: Speed, Conjunction, and Molad HaMemutzah
Words of the Rambam: The sun moves ~30 degrees a month (360÷12). The moon revolves once a month. Sun and moon meet once a month — kibbutz hashemesh v’hayarei’ach (conjunction). The month is 29 days, 12 hours, 793 parts.
Explanation: The galgal hamazalos is 360 degrees. The moon comes to the same place in the mazalos every month, and therefore meets the sun once a month.
Novel Points:
– The moon goes not just 12 times faster than the sun, but almost thirteen times faster, because we calculate everything relative to the sun — the moon must not only complete its own 360°, but also catch up to the sun which has itself also moved ~30° during that month.
– Molad HaMemutzah: The month of 29 days, 12 hours, 793 parts is an average. When you take 12 months and divide, you get this number. But if you look at each month individually, sometimes it’s a bit longer, sometimes a bit shorter — in summer longer, in winter shorter (or vice versa). This is not a contradiction or error — it always follows a system, but it’s not uniform.
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3. Molad HaMemutzah vs. Molad HaAmiti — Practical Difference
Explanation: Until chapter 14, for halachic purposes (fixing the calendar), we use the molad haMemutzah, and we don’t need to know where the moon actually is. But for sighting (when we actually need to see the moon), we need to know the molad haAmiti — where the moon actually is.
Novel Points:
– For the calendar it’s not a problem if one Rosh Chodesh in a year will be a day off — “next year it comes back, in total it balances out.” But for seeing the moon you can’t see the moon according to the average calculation alone — you need the actual position.
– The average calculation is actually more true in itself than the true calculation. The average represents how the celestial body moves in itself — uniformly on its own circle. The true is what we see from the earth. So “average” doesn’t mean “not true” and “true” doesn’t mean “more true” — it depends on whose perspective: from the perspective of truth (in itself) the average is more correct; from our perspective (what we see) the true is more correct. If the center of the sun’s sphere were on the earth, the molad haMemutzah would be the molad haAmiti.
– This is illustrated with the example from Shor to Moznayim — the path from Shor to Moznayim is for us much smaller than from Moznayim to Shor, although in itself it’s equal. When the celestial body is in the half of its circle that is farther from us, it covers a large distance but it looks like a smaller arc (fewer degrees). When it’s closer to us, it covers a smaller distance but it looks like a larger arc (more degrees).
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B. The Assumptions (Axioms) of Ancient Astronomy — End of Chapter 14
1. The Three Fundamental Assumptions
Words of the Rambam (end of chapter 14): The Rambam presents the foundations of the astronomical system.
Explanation: The entire system of spheres is built on three assumptions.
Novel Points:
Assumption #1: The earth stands in the center — everything revolves around the earth, the earth doesn’t move.
Assumption #2: Everything is a circle (sphere). Every firmament makes a perfect circle — a sphere. No one actually saw that it’s a *perfect* circle, but we see more or less a circle (it revolves), and it’s also easier to calculate with circles (from the largest circle you can calculate the smallest, etc.). There are also metaphysical reasons (perfection of a circle).
Assumption #3: Each sphere always travels at the same speed (uniform motion). It doesn’t get tired, it doesn’t change. (Not that *all* spheres go at the same speed — but each *individual* sphere remains constant.) This is directly against what we see — we see that the moon sometimes goes faster, sometimes slower.
Both assumptions (#2 and #3) are not directly observed — “nothing that anyone ever saw.” They are theories/models that were assumed in order to be able to calculate. Even the ancient sages knew that it’s not 100% true that everything always stays the same — but for the cycle (a year) it works.
Because they wanted to maintain all three assumptions, they had to add progressively more spheres (up to eighteen spheres for all the planets — two for each planet, for different calculations).
[Digression: Aristotle’s Assumption] The Rambam in Moreh Nevuchim mentions that Aristotle held that all spheres must be exactly around the earth (concentric), which makes the eccentric sphere already difficult according to Aristotle.
[Digression: Precession] A question is raised about long-term drift (precession) — this is dismissed: “Forget precession, we’re talking now about what happens within a cycle.”
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2. The Solution: Galgal HaYotzei Min HaMerkaz (Eccentric Circle)
Explanation: If each sphere travels constantly, why do we see that the moon (and sun) sometimes go faster, sometimes slower? The solution is called galgal hayotzei (eccentric circle): the center of the sphere of the sun/moon is not the same place as the center of the galgal hamazalos (where the earth stands). Therefore, although the sphere always travels at the same speed, one side of the sphere is closer to the earth and the other side farther — and this makes it appear as if it sometimes goes faster, sometimes slower.
Novel Points:
– This is “simple in essence” — if you make such an assumption, you can reconcile both assumptions (constant speed + circle) with what we see (variable speed).
– The two types of spheres that were devised are: (a) spheres with a displaced center (eccentric/galgal yotzei), and (b) epicycles (galgalei hakafah).
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3. Galgal Hakafah (Epicycle)
Explanation: Besides the eccentric circle, there’s another problem: we sometimes see that a planet (especially the moon and other planets) goes backward — retrograde motion — relative to the mazalos. This cannot be answered with the eccentric circle alone.
Novel Points:
– To reconcile the backward motion, they devised the galgal hakafah (epicycle): a small circle that rotates on the large circle, perhaps in an opposite direction. The planet travels on the small circle, which itself travels on the large circle. Through this it sometimes comes out that relative to us it appears as if the planet is going backward.
– You can even add an epicycle on an epicycle when necessary.
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4. The Transition to Modern Astronomy (Copernicus, Kepler)
Novel Points: Later came Copernicus, Kepler, and others, who removed all three assumptions:
– Instead of everything revolving around the earth — everything revolves around the sun (heliocentric).
– Instead of perfect circles — ellipses (ovals).
– Instead of uniform speed — non-uniform motion (Kepler’s second law).
The main advantage of the new system is that it’s simpler to calculate — you don’t need spheres, you don’t need small spheres — many complicated calculations fall away. What is the “truth” is still a separate question, but practically it’s much simpler.
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5. “Chukei Zman Nasan Lahem Shelo Yeshanu Es Tafkidam” — Old vs. New
Novel Points: The Rambam brings the verse/statement “chukei zman nasan lahem shelo yeshanu es tafkidam” — that the celestial bodies adhere to fixed rules. This is not the same rule as today. Today we don’t hold that they must travel uniformly in circles. The things that don’t change (constants) are different — more abstract physical laws (like gravity). The moon does not travel uniformly, and we don’t hold to the assumption that it must. It returns to the same place, but not because it must be so from a compulsion of circles, but because the physical forces (gravity etc.) bring it about. There are all kinds of details — a celestial body is closer to another body, it gets pulled, etc.
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C. Precision of the Rambam’s Calculations According to Modern Science
Novel Points:
– Lunar calculation — The lunar month of 29 days 12 hours 793 parts (29:12:793) is still more or less accurate, perhaps to only a few seconds. The lunar calendar still works today.
– Solar year calculation — is a bit off, a few hours. Every hundred years we lose a day. This is enough for a calendar, but needs to be fixed occasionally. A practical difference: Tekufas Nissan already falls in the middle of Pesach today, which shows that the calculation of the solar year (Tekufas Shmuel — 365 days and 6 hours exactly) is not accurate enough. This is not because nature has changed, but because the calculation of how long a solar year is, is not precise enough.
– Tekufas Rav Ada — is also off by a few minutes each year, which comes out to a whole day after many years.
– Regarding the moon’s position — the Rambam’s calculation of where we’ll find the moon is still practically correct, even if the physical model (spheres) is not correct. The Rambam himself says in certain places that perhaps the assumptions are not correct — the main thing is that we should be able to calculate.
– Why are the sun and moon themselves round (spherical)? — Today we explain this through gravity which pulls everything to the center, not through Aristotle’s reasons.
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D. Chapter 11, Halacha 2 — “Kabbalos MiPi HaChachamim V’Ra’ayos SheLo Nichtvu B’Sefarim HaYedu’im LaKol”
Words of the Rambam (Chapter 11 Halacha 2): “And furthermore, we have regarding these principles kabbalos mipi hachachamim and proofs that were not written in the books known to all.”
Explanation: The Rambam explains why he’s writing this book — he has information that’s not accessible in the well-known books.
Novel Points:
– Rabbi Avraham Kanievesky’s interpretation: He interprets that “sefarim hayedu’im lakol” means books of the gentiles (scientific books in other languages), not holy books. This means: the information is not in lashon hakodesh, but in the books of the sages of the nations of the world.
– Question on this: If so, does the Rambam only mean that he’s doing a favor for Jews who only know lashon hakodesh? This sounds strange.
– An alternative explanation: The Rambam is not talking about Gemara — he’s talking about the ancient gentile sages who had doubts, and later it was figured out. In addition to this the Rambam has kabbalos mipi chachamim — this means traditions from our sages (Abaye, Rava, prophets, or others), which don’t appear clearly in Maseches Rosh Hashanah.
– The preferred explanation: The Rambam asks himself a question: why should I write this calculation? Go to an astronomy course and learn it there! The Rambam answers: there you’ll learn “sefarim hayedu’im lakol,” but I have for you certain information (kabbalos mipi hachachamim) that you won’t find there. This is the added value of his book.
– Important context: The Rambam said earlier that true calculation (seeing the moon) we don’t need to know nowadays for halacha — only in the time of sighting, or today to know the greatness of Hashem. But he goes through all the halachos that are relevant nowadays.
[Digression: Rabbi Chaim Kanievsky’s Commentary] It’s mentioned that Rabbi Chaim Kanievsky has a commentary on Hilchos Kiddush HaChodesh where he explains the same astronomical matters in Charedi/Chassidic language. This is noted as an “interesting thing” — he gives the same content but in a different style.
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E. Chapter 11, Halacha 12 — The Sun’s Daily Motion
Words of the Rambam: “The average motion of the sun in one day, which is twenty-four hours — fifty-nine parts and eight seconds.”
Explanation: The average motion of the sun in one day (24 hours) is 59 chalakim (degrees) and 8 seconds (seconds = seconds of degrees, 1/60 of a chelek).
Novel Points:
– This means a day is a bit more than 24 hours in relation to the sun’s motion — 24 hours, 59 chalakim, 8 seconds.
– Therefore for ten days — for 10 days it comes out to 400 degrees (TNM), 1 chelek, 5 degrees, 13 seconds. Mnemonic: TNM KG.
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F. Digression: Kiddush Levanah — Until When Do We Make It?
[Digression:] The matter of Kiddush Levanah is discussed — until when do we make it?
– The Beis Yosef (Orach Chaim Siman 426) brings in the name of the Maharil that one should not make Kiddush Levanah after half the month (14-15 days).
– A strong opinion is presented: One should make it in the first few days when the moon is truly “new.” The custom to wait until 7 nights and then make it from 7 to 14 is criticized — “it’s foolish,” because at 7 days the moon is no longer “new,” it’s already a large moon. The word “chadashah” (new) fits better to the first days.
– A humorous remark: “It must be out of chezkas nefel perhaps” — a joke that we wait 7 days like with a newborn child.
– The Rambam himself doesn’t speak about Kiddush Levanah in Hilchos Kiddush HaChodesh — this belongs to Hilchos Berachos, Orach Chaim Siman 426.
📝 Full Transcript
The Foundations of Astronomical Calculations in Hilchos Kiddush HaChodesh
Introduction: The Basic Foundation of the Calculations
Speaker 1: The basic foundation of how the calculations work is built on what? On what was learned in Chapter 11 essentially, that the sun and the moon and all the stars revolve around the world, or at least they appear to revolve around the world in order.
What does it mean they revolve around the world? When they say that the sun revolves around the world once a year, it means to say that it revolves through the galgal hamazalos (zodiac wheel) in a year’s time, because every day it revolves around. But the very basic thing is that once a year it comes to the same angle, to the same place in the sky.
Speaker 2: To the same angle, to the same place in the mazalos (constellations).
Speaker 1: But we see it in the same place in the sky.
Speaker 2: We see it toward north and south.
Speaker 1: No, we don’t see it toward north and south. That’s not correct. We see it toward… This isn’t the most simple thing. The most simple thing to learn the whole thing isn’t that. The most simple thing to learn the whole thing is we see it relative to another mazal (constellation). In mazal Tishrei, in the constellation of Tishrei, and so forth. That’s the…
Speaker 2: Mazalos is already a greater wisdom.
Speaker 1: No, it’s not a greater wisdom. How does one know? Someone who doesn’t know mazalos, that a year has passed?
Speaker 2: No, everyone knows mazalos. One can see the mazalos.
Speaker 1: You don’t understand what you’re saying. They already followed this. The basic thing that all these calculations are built on is that, not what you’re saying. We don’t see anything about north and south. Everything is about the mazalos. Okay? That’s the basic thing. You don’t know about mazalos, you think mazalos is some fancy thing, I’m telling you it’s not. I already spoke about this, went through this once.
The Movement of the Sun and the Moon
Speaker 1: What the essence is, so the sun comes, it goes through, and the mazalos is three hundred and sixty, a circle of mazalos for example, which is the path that the sun travels, is three hundred and sixty degrees. It comes out that every month it moves thirty degrees. Okay, that’s one thing.
The moon, for example, doesn’t go shorter, the moon goes faster. The moon comes every month to the same place. Right? The moon revolves around the world every month. Every month it comes to the same place in the mazalos.
It comes out that once a month, for example, the sun and the moon meet, called kibutz hashemesh v’hayarei’ach (conjunction of the sun and moon). The moon is in a constellation, which constellation I don’t know, in the same place where the sun is once a month.
It comes out that the moon goes a bit faster. You want to know? It comes out that the moon goes a bit faster than the… not a bit faster, very much faster. Much faster, not just twelve times faster, but almost thirty times faster. Because meanwhile, everything is calculated relative to the sun.
Yes, everything goes the same way, from east to west, everything. Except for the world, which perhaps revolves in reverse, because that’s every day. But in any case, yes, everything goes in reverse, from east to west, and… through the fact that we calculate. There are sometimes things that we see in reverse, then it’s a problem. But generally speaking, everything moves in one direction.
The Speed of the Moon Relative to the Sun
Speaker 1: So therefore, that the moon goes a bit faster than the sun, and not faster than the sun, plus thirty. It goes thirteen times as fast as the sun, for the moon, according to the calculation, because it also catches up with the sun.
Anyway, now, the interesting thing is this, what’s the interesting thing? That how does one calculate this? So we know, let’s say we know how long it takes, one could have theoretically calculated also how long it takes, also how precisely it will be according to the calculation that we say, that is, you know which constellation we’re holding, which month, you’ll know precisely how it will be.
But there’s an interesting thing, which is, that in practice it doesn’t go equally, in the summer it takes longer, and the winter stands shorter. We don’t see that it comes every year, every month, the moon to the same place.
Molad HaMemutzah: The Average Calculation
Speaker 1: Now there’s the question why. Someone who pays attention sees that the next month the sun and moon meet a bit later, and so forth, not exactly according to the calculation that theoretically should have been. So the sages… but it evens out over the year as if?
Speaker 2: One minute, yes, that’s very good.
Speaker 1: About this we say, as it is written molad hamemutza (average conjunction). What does hamemutza mean? If we say that the month is 29 days, 12 hours, 793 parts, that if one took twelve times that and divided it back, it became so much. If you look at each individual month, sometimes it’s a bit longer, sometimes a bit shorter. That’s a fact.
And it’s very interesting, because it’s not a contradiction, it’s not as if it became distorted, because it always goes with a system. If someone had only made observations for a few days, he would have said, “It’s not always exactly as I calculated.” No, no, exactly. This is what’s called the molad hamemutza or the kibutz hamemutza (average conjunction). This is the average, literally, it’s an average.
Why Do We Need the True Molad?
Speaker 1: Now, why do we need to have this? If so, it comes out that when you want to know where the sun is, how the moon will be, it’s not enough to use the molad hamemutza. You need to know the true one.
Until Chapter 14, regarding halacha, if you ask regarding halacha, one goes with the average, and it’s not relevant how the moon truly is. But regarding sighting, one needs to see how the moon truly is. One needs to figure out something more than that.
The Two Assumptions of Ancient Astronomy
Assumption #1: Everything is a Circle
Speaker 1: Now, how technically did they learn that it works? I’ll tell you what Reb Elazar explained to me. One minute, I’ll just tell you what he explained to me.
They understood it this way, what’s the explanation? How can it be that why is it overall the same and sometimes it’s different? They said this way, an assumption was made. The assumption was that… and the assumption is nothing that anyone ever saw.
An assumption number one was made – the Rambam brought the assumption at the end of Chapter 14 – assumption number one is that every firmament that we see in the sky travels in a circle, a perfect circle, called a galgal (sphere), a perfect circle. It travels it. An assumption. No one saw it, it could be… not simple that we see it in such a perfect circle.
We see it more or less in a circle, because we see how it revolves around and around. There are differences, there are times when it goes faster and slower. There’s such a simple reason to think that everything is circular there. Okay, there’s a metaphysical reason, it’s also more or less true, but not exactly a circle in any case. There are all kinds of reasons, both fancy reasons and simple reasons, but they decided, everything is a circle, also easier to calculate with a circle. Everything is a circle.
Speaker 2: Is a circle easier to calculate the calculations?
Speaker 1: Yes, imagine if not, presumably there’s a way, but it’s a bit more complicated. But a circle, if you’ve said that the largest circle you can know what the smallest circle is, etc. with calculations, with that math. It’s very easy to calculate, it’s more or less the essence.
Assumption #2: Every Galgal Always Travels at the Same Speed
Speaker 1: Assumption number two they decided that each one of the circles always travels at the same speed limit, at the same speed. It never goes faster or shorter. Another assumption, another assumption.
Speaker 2: That all are driven at the same speed?
Speaker 1: Not all at the same speed. Each one always goes at the same speed. It doesn’t slow down, it doesn’t change. If one travels thirty miles an hour, it travels thirty miles an hour. Never. It’s not sluggish in the summer and peppy in the winter. And other galgalim (spheres) go at other speeds. They see them. They see the moon that the galgalim go at a different speed than the sun, right?
Speaker 2: But the two other things. You should be assumptions.
Speaker 1: No, by the assumptions it’s based on, for example that the moon goes at a faster speed, because we see it’s in such a place once a month. Very good, but that the moon always goes at the same speed, that we don’t see. We see exactly the opposite. That there are sometimes a bit, yes? Sometimes it’s a bit longer.
We just learned this now, but there are months that are longer than other months. If we go with our eyes to seek the moon, it will take longer one month than a second month. In the winter I mean longer, in the summer shorter, or vice versa, it’s different. It’s not true that it travels equally.
But for our calculations we decided it, and also for good reasons and other reasons we decided it, that every galgal always travels uniformly.
Discussion: Can We Lay Out the Calendar for Many Years?
Speaker 2: Ah, if so it’s difficult, if it travels… the whole thing that we can lay out the calendar for many many years is based on the fact that everything goes uniformly.
Speaker 1: No, no, no.
Speaker 2: True, true, it could be over the course of years it could become more and more off.
Speaker 1: No, no, no, you’re wrong. I’m talking about what happens in the year, in a year, okay? The calendar isn’t… we’re talking now about the calendar. Forget the calendar. I’m talking now about what actually happens in the sun. And don’t say it becomes faster because tomorrow it becomes heavier. In one year, okay? In one cycle. Within a cycle. We want to figure out how one cycle works. If the whole cycle begins to learn not against.
Speaker 2: Another question. It’s actually also true.
Speaker 1: They also knew that it’s not actually true, that everything always remains the same. But that’s another thing. And what we’re talking about is just a simple thing. And the moon, today we’re only learning about the moon, okay? Kiddush hachodesh (sanctification of the new month) is only about the moon, there are only wisdoms about the sun and the stars, and there’s still much more about the moon.
Okay, the moon doesn’t take every month 29 days, 12 hours, 793 parts. A calendar we can make because we don’t care about when we make the calendar, or because on average it’s correct. So what do we care if one Rosh Chodesh in the year will be a day off? The next year it comes back, there’s when we count overall and so forth, it’s not a problem. That’s for the calendar it’s not a problem. The problem is only for the sighting, you want to see the moon you won’t be able to see according to the calculation.
The Answer: Galgal HaYotzei (Eccentric Circle)
Speaker 1: Now, I’ll just tell you now how the astronomy worked, the basic thing of the astronomy worked. And what’s different today? Or the very very basic thing.
They make assumption number 1 is everything a circle, and number 2 is a certain circle, a certain sphere. A circle isn’t a sphere. A certain sphere. In English one says sphere, in Yiddish sphere? No, I don’t know. Anyway, a certain, a globe, yes, not a circle, I don’t know how to say it, a kadur (sphere) in lashon hakodesh (Hebrew), not an igul (circle), a kadur.
Every kadur always travels at the same speed, it doesn’t get tired, and so forth. If so it’s difficult, if it travels the same speed, the answer is directly against what we see. We see the moon, sometimes it goes quickly, sometimes it goes slowly, sometimes it goes faster, sometimes slower, and meanwhile it says, what’s the answer?
The answer is called, the answer is called, the answer is called galgal hayotzei (eccentric sphere). Okay, it’s sometimes called, galgal hayotzei. What’s the answer? That the sun is the center of the galgal of the sun is not the same place as the center of the galgal of the stars, the galgal hamazalos.
And we already saw this yesterday, and we showed that it’s actually simple. If you make such an assumption, both travel at the same speed. Nevertheless, the galgal of the sun goes around the world, but it’s closer, one corner of its vessel is closer to
Astronomy: Galgal Yotzei Min HaMerkaz, Galgal Hakafa, and the Assumptions of Old and New Astronomy
Continuation: The Difference Between Average Calculation and True Calculation
Speaker 1: Although in itself it travels at the same speed. Right?
Speaker 2: Right.
Speaker 1: The distance it travels here at such a speed, but relative to earth… look at the picture, yes, yes, yes, very simple. It travels all the time. If you have such a circle, it travels all the time. But in the… and here it takes… and the upper half which is farther from us, which travels a whole half. Here, when we see… yes, what we see in the wind in the half is only from here to here. It’s much smaller than from here to here.
Speaker 2: Right.
Speaker 1: It perhaps looks to us completely round, but it’s not truly completely round. One can see that it’s as if such a picture from the side and such a picture from the side. But therefore here it moves from this point, yes, here are the two sides of the galgal, right? We say from Shor (Taurus) to Moznayim (Libra), right? So from Shor to Moznayim, it doesn’t travel from here to here, it travels from here to here, which is much smaller. Because conversely from Moznayim to Shor it travels from here to here, so much longer. It’s longer relative to us, but not in itself.
This resolves the difference between the molad, the average calculation and the true calculation. The average is actually more true than the true, you understand? Because the average is what truly travels. What we call average and true isn’t simple that average didn’t happen and true is truth. That is, it depends how you look. From our perspective the true is what you’ll actually see the sun, and the average is just a running calculation. But from the perspective of truth, the average is how it runs in itself. If the circle of the world were here, the center of the galgal of the sun, around that it actually travels in the molad of the average, in the average calculation. But to see it for us one needs to go with the true.
Speaker 2: Right?
Galgal Hakafa (Epicycle)
Speaker 1: And not only that, for several reasons another thing was added, okay? Not only what’s called the galgal hayotzei (eccentric sphere), and afterwards there’s a thing called the galgal hakafa (epicycle). Galgal hakafa means that not only that there are times when it goes backwards. This can’t be answered with that answer, okay? Therefore one needs to find another answer. I feel he doesn’t show it so well here. Another answer. It goes backwards. Why does it go backwards? The sun and the moon sometimes go backwards?
Speaker 2: Yes.
Speaker 1: You didn’t know?
Speaker 2: No.
Speaker 1: Again, backwards we speak everything relative to the mazalos. It could be the moon one day we see it here, and tomorrow we see it theoretically on the other side. Now, how do you account for this? Not always, sometimes it goes backwards.
Discussion: Mazalos and World — What Moves?
Speaker 2: Are we certain that the moon moved and not the mazalos or our world?
Speaker 1: Don’t ask questions now. We assume that all these things move?
Speaker 2: Our world doesn’t move. That’s the assumption of all the…
Speaker 1: But the moon and the mazalos move, or are the mazalos always fixed?
Speaker 2: No, mazalos move certainly.
Speaker 1: So, we don’t know which moved more.
Speaker 2: No, no, we always calculate the mazalos don’t move. They move every day, every twenty-four hours like the day and night. But in this calculation they don’t move. They’re in the same place in the degrees. Degrees means mazalos.
Speaker 1: The truth is that they themselves also move, but it takes seventy thousand years. Whatever, it’s a very long… the mazalos themselves change in their galgal. Their galgalus (spherical motion) also rotates, the Rambam already says, and this was always known. About this today the mazalos aren’t in the same place as their names are. What we call mazal Shor, you should see how the picture of the shovel. It also looks true. But it looks slow enough, not to be relevant. I mean not everyone, the mazalos remain fixed and established. Fixed and established is that they only move once a day. Understand? But not further to themselves.
Continuation: Galgal Hakafa
Speaker 1: The sun and the moon move in an orderly fashion in honor of this. But sometimes one sees, not only the moon incidentally, also the other planets, sometimes one sees that it goes backwards. Backwards. This is the greatest problem. Going backwards creates a great difficulty for our theory of circles. Therefore, they invented a new innovation called epicycles, okay, in English, or in Hebrew “galgal hakafah” (circle of rotation).
Galgal hakafah means it makes rotations? No. It means that besides the fact that there is a large circle that rotates around, there is also a small circle that rotates perhaps in the opposite direction. As if, in the picture I feel it’s a funny picture, but understand, the whole circle travels around, but it also travels on another circle. Therefore, sometimes, somehow it comes out that relative to us it’s reversed, simply because of the smaller circle, and perhaps we’ll add a rotation upon the rotation. In short, it becomes complicated, this is all in order to reconcile, so the calculation should work out, even though we see it sometimes reversed.
Discussion: Other Movements
Speaker 2: So these are the main lines. One also sometimes sees it goes forward faster than it should be?
Speaker 1: No. Also, also, I don’t know. And similar, such sorts of things, I don’t know. When you say that one sees, also one must know, sometimes they didn’t see, and today we have better telescopes, perhaps one sees yes, and so on. Also, many times when it says there, sees, it could be that a record from an earlier generation doesn’t match with a record that someone makes of what he saw today. So he said, so one must know, you see modestly, perhaps they didn’t see correctly. The tomorrow that was said, becomes punctually, becomes questions about his telescope. So anyway, just will be clear, just will be clear, just who is there, and the fear which week that are there.
The Three Assumptions of Ancient Astronomy
Speaker 1: And we say that there are generally ten, we mean that there are only such great circles. Because truly, the many circles are eighteen. Why? In order to be able to calculate all the movements that we can see from the planets, there must be eighteen, two for each planet, because of such calculations. And the two, he did, there are two sorts of things: one is that the spheres don’t all have the same center. That’s one thing, that’s still one sphere. Besides that, sometimes one adds another whole sphere that travels as it were on the small sphere, and it’s an independent rotation, and this is called galgal hakafah, or in English “epicycle.” Okay?
And now, the story was as follows, what’s interesting is that this way one can understand, this is basic. The main reason why the assumptions were built on these three assumptions — let’s say the world stands first — it seems they very much wanted to maintain the assumptions of the circles, that they wanted to maintain three other assumptions, three assumptions that they held very strongly.
Assumption number 1: The world doesn’t move, and everything moves around us.
Assumption number 2: Everything moves in perfect circles. Incidentally, this was also already, the Rambam already knew that there are movements not in perfect circles, perhaps it’s an oval, here one still goes with perfect circles, but they already knew then. All doubts already existed once, it’s a list part of them. But in any case, what we’re learning here, and also what we’re learning is not perfect circles.
Another thing, but the assumption number here is perfect circles. And another number three: that every outer circle travels outer, and therefore one cannot reconcile any hundred, and sometimes it travels it comes out so, it always travels the same line. Also a certain thing makes it easier to calculate, you follow each one. Okay.
And a third assumption, what is the other assumption? These are the three assumptions, so therefore the other assumption is for example, the Rebbe says that Aristotle would have had an assumption that all spheres must indeed be around the world precisely, and it’s not shameful to have the spheres, from then it’s generally difficult.
Because of all these things, often I mean, other people invented it because of many kosher things, but they always wanted to maintain an assumption of perfect circles, and the assumption that every outer circle travels with its same speed limit, and the assumption that the world stands in one place. Therefore they had to continuously add spheres.
The Transition to Modern Astronomy
Speaker 1: This is the basic. Later came the people Kepler, and what is named Copernicus, and other righteous ones, who decided that already before this various assumptions were removed, and therefore they decided that one can instead of saying that everything rotates around the earth, one can have an assumption that everything rotates around the sun. Removed the assumption that it must travel in circles, removed the assumption that it must travel equal, removed the assumption that the world is in the center. Therefore came out a different calculation that comes out simpler to calculate. The main advantage of this is simply that it’s simpler to calculate. What is the truth is still a question. But the astronomers figured out that it’s simpler, one makes less convoluted calculations. That’s all the story of today’s. And with the new calculations no spheres are needed. Not any spheres, not small spheres, not large ones, many things are not needed.
Discussion: “He gave them laws of time that they should not change their function”
Speaker 2: I believe that this is mainly the spheres. Because the fact that generally they maintain the same constancy, the “He gave them laws of time that they should not change their function” that the Rebbe brings this, isn’t today a rule that generally… not in this way.
Speaker 1: But how then does one make predictions on calendars?
Speaker 2: One can make predictions, but not with this assumption, not with finding rules that everything travels equal. There are other rules, that the actual unchanging things are different. It’s more abstract according to today’s thing. There’s no assumption, there are no spheres, there’s nothing at all that wants to travel equal. The moon doesn’t travel equal, and they don’t hold from the assumption truly.
Speaker 1: So one can’t say that the moon returns to the exact same place?
Speaker 2: Certainly it returns to the exact same place, but not that it must be so. There’s no compulsion.
Speaker 1: And one questions that it was so for thousands of years, or only that it will be so forever?
Speaker 2: No, that’s not the question. This is the main thing: when the assumption that every thing travels, that it doesn’t move faster for example, that’s not entirely true, for example. Because there are opposites, I don’t know, it’s all these assumptions, not because I have a heavy mood, because gravity works so, because there’s gravity from here, and it’s closer to that one, it writes to that one. There are all kinds of details.
Laws of Sanctifying the New Moon: Precision of Calculations According to Modern Science and Law 12 — The Sun’s Movement in One Day
Precision of the Rambam’s Calculations According to Modern Science
Speaker 1: Has a degree in itself, this is still believed today more or less. But that in this manner that the sun must travel on a perfect circle and it doesn’t move, this is not believed. Besides the fact that the sun presses, in short, all these differences. But the main thing is already up to here, up to here is the basic history of how it works the but more or less, just to be clear, more or less what the Rambam is going to say is still true. This is important to know.
If you want to know either the Rambam’s calculations of the commandment, what is it still, that the moon is 29 days 12 hours 793 parts, is still more or less correct. The calculation of the solar year is a bit off a few hours, as we have seen according to what we know today. But again, you’re not very far off, at most, and every hundred years one loses a day. Okay, one still needs to fix it, but it’s enough for a calendar, more or less, one still needs the same all calendar, and it’s still not so twisted.
There’s one problem. It already happens today that the spring equinox happens already in the middle of Passover. It already happens today. Okay, it’s a small matter, we need to fix it. And this can have to do with changes in nature, not in the calendar. And this has to do with the fact that the calculation, how long, their calculation, how long the solar year is, is not correct.
Speaker 2: Isn’t it because things become warmer or one of the calculations?
Speaker 1: No, no, no, this is about the spring equinox. The spring equinox is an astronomical thing. Ah, how the thing comes to the same place in the sky. And it’s a calculation how long the year is, a calculation that the calendar is built on, which is that the year is exactly 365 days 6 hours. The tekufat Rav Ada, in other words, called at first precise is not precise. The tekufat Rav Ada is also off with… I don’t remember how much time, a few minutes each year, but nothing each year comes out… a whole day after many years.
So, the moon’s calculation for example is yes, I mean, more or less, perhaps off a few seconds, but the day of Passover on the 15th of Nissan is more or less precise according to what is known. So, therefore, the calendar of the moon still matches today. And the same thing, also, what the Rambam is going to tell us where the moon is, is more or less correct. Even if it’s not on a sphere, it’s still however approximately…
Speaker 2: No, for the calculation, not only it’s approximately, it’s the same place.
Speaker 1: What he tells you, his physical standings, how far it is, how the sphere is, whether there’s a sphere or not, this is not done in today’s slang. Therefore, in other things it makes a bigger practical difference. But regarding the details of the moon, that still, that to make his calculation, you will supposedly generally have arrived at the correct conclusion where one will find the moon.
What, it’s built on what one sees not, one sees. Very easily, and it’s actually made assumptions how one should be able to calculate it. The Rambam himself in certain places says that perhaps the assumptions are not correct, the main thing is that one should be able to calculate. That it goes in a circular way, or it can sometimes go in a straight line, or it appears to us as a circle because the way how we are we together to the… according to what we learn today it doesn’t go exactly in a circle, but that’s still a circle. And it appears to us that it goes in a circle.
The sphere is strongly based on the fact that it goes in a circle. Today one says that the orbits of the planets are not a circle, it’s only something like an oval. This also answers the same question that they had, why sometimes it’s longer and sometimes the end is answered literally. One doesn’t need to add the centers and all these things. Besides that, it goes around the sun. Part of this, regarding the moon I don’t know, the moon goes yes, and supposedly what was in the world. Also doesn’t need it’s not exactly, I don’t remember. But this was other things. This answers many of the questions without… We also don’t know if what we see always as a perfect circle is a perfect circle, and these are the moon.
Speaker 2: Outer, I’m not talking about the sun, I’m not talking about the orbit, not about the sun on the sun. I’m saying that the sun and the moon themselves are perfect circles.
Speaker 1: Perfect circles, yes?
Speaker 2: Yes, yes, yes, gravity makes them so.
Speaker 1: That’s what is said today. There’s a reason why they’re usually circles, and not exactly the reason that Aristotle thought, but the reason is gravity. It pulls things to the center. So everyone pulls things to the center, so everyone is as close to the center as possible with all layers and… more or less who it is… Okay, already, up to here the matter.
Law 12 — The Sun’s Movement in One Day
Speaker 1: Now we can learn the holy Rambam. Twelve, you’ll understand a Yiddish word. Okay? Says the holy Rambam:
“The mean movement of the sun in one day, which is twenty-four hours — fifty-nine parts and eight seconds.”
Speaker 2: Eight?
Speaker 1: It’s without a tav-kuf, okay. It’s without a tav-kuf, okay. It’s without a tav-kuf. What does it mean? 24 plus 59 parts and 8 seconds. Okay?
Speaker 2: Yes.
Speaker 1: A day is a bit longer than twenty-four hours. That means a day is twenty-four hours, it doesn’t start not. It’s twenty-four hours, 59 parts and 8 seconds. Okay?
Is this correct? What one can all capture in a day. What?
“It comes out its movement, how much comes out ten days, is 400 degrees, and one and five parts thirteen seconds, sign tanmakh 23.”
Again.
Digression: Rabbi Chaim Kanievsky’s Commentary
Speaker 2: What does Rav Chaim Kanievsky learn? How does he make such things in a Hasidic language, all these things?
Speaker 1: This is the funny thing about Rav Kanievsky. He explains the same thing supposedly, only in the way of Hasidism, in Haredi language. How is it? Put 70 honor in a year, why don’t I find it? Kanievsky. He moved closer to me. He’s still a Jew, what does he say about all these things?
Chapter 11. Levusha, mahar, well, I want to see what he says about chapter 11. Do you agree with me?
Speaker 2: Yes yes.
Speaker 1: Sarah midim, Hebrew language. Yes.
Discussion: Rambam Chapter 11 Law 2 — “Traditions from the sages and proofs that were not written in books known to all”
Speaker 2: What is the gimel here, gimel goes on which words?
Speaker 1: Not gimel I’m sorry, gimel he said with the Rambam, it says that “and they are not in books known to all”, he translates that it means to say… where is it? Which words does it go to? The Rambam… Okay, we’ll learn chapter 11 again today.
The Rambam, when he says “and they are not in books known to all”, and speed… and more, very interesting. Ah, do you remember we asked the question? The Rambam said that… why does he write this? Because according to the Rambam’s way there was first a dispute with doubt, and after much time they discovered some of the rule, “and besides this we have regarding these principles traditions from the sages and proofs that were not written in books known to all.”
What does this mean? That he has some tradition person to person from Ezra the Scribe? Says Rabbi Avraham Kanievsky that he means that it’s not in Hebrew but in the books of the gentiles.
Speaker 2: Very funny, if so it means to say…
Speaker 1: Yes, this is weird, he means to say I help that the poor Jews who can have Hebrew? I thought that he means to say that he knows it… why doesn’t everything stand in tractate Rosh Hashanah?
Speaker 2: No, but he says “traditions from the sages and proofs that were not written in books known to all.”
Speaker 1: I don’t think he’s right in this. He’s not talking about the Gemara righteous one, he’s not talking about the Gemara, he says, he starts clearly… all books that Jews have, it doesn’t stand from all books. He starts to talk about the ancient gentile sages, he’s not talking about the Jews at all in the whole book, okay?
In law 2 it talks about the ancient gentile sages who had doubts. And today have figured out. “And besides this we have traditions from the sages.” And therefore I’m going to write these things. It’s not in the Gemara, it’s only I wanted it. Just look at this piece. “And furthermore we have regarding these principles traditions from the sages.” It translates, the name of our sages translates from I don’t know, Abaye and Rava or the prophets, however the sages are. But we were written in tractate Rosh Hashanah.
The Rambam has a problem, because other laws, other matters are… he doesn’t say Shabbat, he only says tractate Shabbat. Sanctifying the new moon from the Rambam is so little. He says, no, the sages also knew about this, but one doesn’t see it clearly in tractate Rosh Hashanah.
Speaker 2: He doesn’t mean that.
Speaker 1: No, that’s not what he says. He’s justifying himself for something else. He’s justifying himself, why am I writing a book if everyone knows it? Something like that. He says, I know certain things that don’t stand in all books.
The simple plain meaning of what the Rambam says here is, that you want… The Rambam asks on himself like a question, I want to tell you the calculation. You’ll tell me, well well, go to college, there is an astronomy course, you’ll learn. Says the Rambam, no, there you’ll learn books known to all, but I have for you certain information that you won’t learn there, that will help you. That’s how I would understand the Rambam, not that he means to say that it’s not in the books of the gentiles, because that’s not the subject at all.
Digression: Blessing the Moon — Until When Does One Make It?
Speaker 2: Interesting, he says that in our time, yes, look what he says, he brings all the laws that apply, that are practiced in our time. You remember the Rambam said that the true calculation one doesn’t need to know at all in our time, only in the time of visual sighting, or today in our time to know the greatness of Hashem, as we learned, but not for halacha. He goes through all the laws that could be, that apply to the festivals. For example, look at his examples, I can be here sometimes.
So, there is Kiddush Levana (sanctification of the moon) which one only does for half a month in the appointed time, and this goes… It’s interesting, you see? He brings a Beit Yosef. Very weird. What is the Kiddush Levana? It’s a Beit Yosef that says, in the name of the Maharil, this is the entire source, that one does… one should not do after half a month, one should no longer do it. And this half month, however, is not counted from the… Kiddush Levana was made upon seeing a new moon, right? So he says, until when is it new? Until half a month.
Speaker 1: By the way, it’s extreme. I hold that one should do it the first few days. The laws of Kiddush Levana are very funny to me, yes. A new one, that means, on Rosh Chodesh one should do it, the day after we’ll be able to see it. First few days, what? Why wait seven complete nights? It’s foolish. In the end you have from seven to fourteen.
Speaker 2: Yes, and it’s the wrong time, then it’s already not new. The claim is it already has a large moon.
Speaker 1: It should be out of the presumption of miscarriage perhaps.
Speaker 2: Do you want me to laugh or cry? I don’t know. How does he bring this Yosef tav-kaf-vav?
Speaker 1: I can’t, I haven’t yet learned the laws of the moon, the Rambam doesn’t speak about this.
Speaker 2: The Rambam doesn’t speak about this. Of course, in Hilchot Brachot, Orach Chaim tav-kaf-vav.
Speaker 1: Ah, ah, ah, I meant in chapters.