The Presidency of the Sanhedrin was a Shadow Monarchy

Mishnah Hagigah 2:2  lists the Nsei'im who preceded Hillel:

יוסי בן יועזר אומר שלא לסמוך, יוסי בן יוחנן אומר לסמוך.
יהושע בן פרחיה אומר שלא לסמוך, נתאי הארבלי אומר לסמוך.
יהודה בן טבאי אומר שלא לסמוך, שמעון בן שטח אומר לסמוך.
שמעיה אומר לסמוך. אבטליון אומר שלא לסמוך.
הלל ומנחם לא נחלקו.
יצא מנחם, נכנס שמאי. שמאי אומר שלא לסמוך, הלל אומר לסמוך.
הראשונים היו נשיאים, ושניים להם אבות בית דין.

Translation from Sefaria:

Yose ben Yoezer says not to lean hands [on the Chagigah sacrifice]; Yose ben Yohanan says to lean hands. Yehoshua ben Perahia says not to lean hands; Nitai the Arbelite says to lean hands. Yehuda ben Tavai says not to lean hands; Shimon ben Shetach says to lean hands. Shemaya says to lean hands; Avtaliyon says not to lean hands. Hillel and Menahem did not disagree. Menahem left and Shammai entered. Shammai says not to lean hands; Hillel says to lean hands. The first [of each pair] was the nasi [head of the Sanhedrin] and the second [of each pair] was the av beit din [vice-head of the Sandhedrin].

So the first five Nesi'im were:

• Yose ben Yoezer
• Yehoshua ben Perahia
• Yehuda ben Tavai
• Shemaya
• Hillel

The Bavli (Shabbat 15a) lists the three Nesi'im who followed Hillel:

הלל ושמעון גמליאל ושמעון נהגו נשיאותן (לפני) הבית מאה שנה 

Translation (including interpolations that are very convenient for my argument) from Sefaria:

Hillel, and his son Shimon, and his grandson Gamliel, and his great-grandson Shimon filled their position of Nasi before the House, while the Temple was standing, for a hundred years

So before Hillel the position of Nasi was not hereditary and following Hillel the position of Nasi became hereditary. That position remained hereditary, except for a short period after the destruction of the Temple while Rabbi Yohanan ben Zakkai filled in while Rabban Gamliel of Yavneh was growing up, and except for a brief time when the position was shared by Rabban Gamliel of Yavneh and Rabbi Elazar ben Azaryah, until the position was abolished by Theodosius II in 425 CE. What caused the change?

Hillel died in 10 CE (Wikipedia; GENi; Encyclopedia.com) or in 8 CE (Chabad) or some time between 10 CE and 20 CE (New World Encyclopedia) . (That's probably enough Googling of "Hillel the Elder" to make my point.)

In 6 CE, Augustus Caesar replaced Herod Archelaus, the last (nominally) Jewish ruler of Judea, with a Roman governor.

Originally, the Nasi had to merit his position by being one of the leading scholars of his generation. What could have motivated the Sanhedrin to change its criterion?

I propose that the motivation was political. I propose that the Sanhedrin made the position of Nasi hereditary in anticipation of turning the family of the Nasi into a royal dynasty of Judea when the Roman Empire falls at some unknown date in the future. This change came, of course, with the downside of the Nasi not necessarily being a great scholar. Rabban Gamliel I (the grandson of Hillel) and Rabbi Yehuda HaNasi arguably were the top scholars of their generation. Rabban Gamliel of Yavneh was outclassed at least by Rabbis Eliezer, Yehoshua and Akiva, which is what led to the rebellion that forced Rabban Gamliel of Yavneh to share his position with Rabbi Elazar ben Azaryah, as described in Brakhot 27b-28a. It also (IMHO) led to Rabbi Meir's failed coup d'etat, as described in Horayot 13b-14a, whose purpose was to restore election of the Nasi based on merit.











The following is Wikipedia's list of Presidents (נשיאים) of the Sanhedrin:

Yose ben Yoezer                     170 BCE - 140 BCE
Joshua ben Perachyah            140 BCE - 100 BCE
Simeon ben Shetach               100 BCE - 60 BCE
Sh'maya                                   65 BCE - c. 31 BCE
Hillel the Elder                        c. 31 BCE - 9 CE
Shimon ben Hillel                   9 CE
Shammai                                 9 CE - 30 CE
Rabban Gamaliel the Elder    30 CE - 50 CE
Rabban Shimon ben Gamliel 50 CE - 70 CE
Rabban Yohanan Ben Zakai  70 CE - 80 CE
Rabban Gamaliel II of Yavne 80 CE - 118 CE
Rabbi Elazar ben Azariah       118 CE - 120 CE
Interregnum (Bar Kochba revolt)
Rabban Shimon ben Gamliel II 142 CE - 165 CE




see also https://www.yeshiva.org.il/wiki/index.php?title=%D7%A0%D7%A9%D7%99%D7%90_%D7%94%D7%A1%D7%A0%D7%94%D7%93%D7%A8%D7%99%D7%9F#.D7.A8.D7.A9.D7.99.D7.9E.D7.AA_.D7.A0.D7.A9.D7.99.D7.90.D7.99_.D7.94.D7.A1.D7.A0.D7.94.D7.93.D7.A8.D7.99.D7.9F_.D7.91.D7.AA.D7.A7.D7.95.D7.A4.D7.AA_.D7.91.D7.99.D7.AA_.D7.A9.D7.A0.D7.99_.D7.95.D7.90.D7.97.D7.A8.D7.99.D7.94
(נשיא הסנהדרין)       

החרדים: יהודים עובדי אלילים של ימינו

לפני אלפיים שנה, עבודת אלילים הייתה עבודת גופים שמימיים. לכן, חז"ל קראו לעבודת האלילים של ימיהם "עכו"ם" (עבודת כוכבים ומזלות). בימינו, מוכר לכל שהגופים השמימיים הם אינם אלים, והאלילים של ימינו הם בני אדם, ביחוד בני אדם כריזמטיים, כמו היטלר, סטלין ומאו. (אם אינך מאמין שהנצים עבדו להטלר, אני מזמין אתכם להסתכל בסרט Triumph des Willens.) גם החרדים עובדים לבני אדם (בנוסף לעבודת הקב"ה).

המקרה הכי בולט של התופאה הזאת הוא אצל החרדים. האדמו"ר הוא אליל. החסידים מכבדים את האדמו"ר שלהם באופן הראוי רק לקב"ה. ראו למשל ערך "קוויטל" בויקיפדיה.

אצל שאר החרדים, האלילים הם ה"גדולים", דרך הדוקטרינה של "דעת תורה".

ויקיפידיה מגדירה את "דעת תורה" ככה:

דעה הבאה לבטא את עמדת תורת ישראל בהתייחס לשאלה כלשהי העומדת על הפרק אשר אין לה מענה בפסיקה ההלכתית. מתוך אמונת חכמים, יש המייחסים לאדם הנחשב גדול בתורה את היכולת לשמש לפה עבור התורה ולהביע את דעתה (שאינה מובעת בה בגלוי) בשאלה הנידונה. מתוך כך מייחסים לאדם כזה את הכושר לפסוק לא רק בנושאים תורניים והלכתיים צרופים אלא גם בנושאי פוליטיקה, מדינה והלכות חיים בכלל. הסוגיות הדתיות שבהן עסק, על פי גישה זו לאמונת חכמים, מזככות את מוחו ומכשירות אותו לפסוק בכלל תחומי החיים.

 כלומר, מי שמאמין בדעה הזאת מתייחס לבן-האדם, שהוא מכיר כ"גדול", כוחות אל-אנושיות. זה בלתי אפשרי לבן-תמותה להכריע בתחום שהוא מחוץ לתורה רק על סמך ידע בתורה ובלי מומחיות בתחום שבו הוא מכריע.

לפי הרב ג'וש יוטר,

  I first heard the term "Gadolatry"  attributed to the late professor Arthur Hertzberg.  A portmanteau of "gadol" and "idolatry", the word "gadolatry" refers to a perceived phenomenon in Orthodox Judaism where select rabbinic leaders are treated with a degree of deference or reverence, bordering on worshiping the person of the rabbi himself.

תרגום:

שמעתי לראשונה את המונח "Gadolatry" ("עבודת הגדולים") מיוחס לפרופסור המנוח ארתור הרצברג. צירוף של "gadol" ו-"idolatry", המילה מתייחסת לתופעה נתפסת ביהדות האורתודוקסית שבה מתייחסים למנהיגים רבניים מיוחדים במידה מסוימת של כבוד או הערצה הגובלת בסגידה לאישיות של הרב עצמו.

בסוף מאמרו הוא כותב

Dr. Hertzberg was correct in coining the term “gadolatry” – not in the sense that those who follow gedolim are idolaters, but in the minds of a non-trival segment of the Jewish population, when one disputes the sacred authority of a gadol, he might as well argue with God himself.

תרגום:

ד"ר הרצברג צדק בהמצאת המילה "godolatry" - לא במובן זה שאלו שצייתים לגדולים הם עובדי אלילים, אלא שבמוחם של פלח לא-מבוטל של האוכלוסייה היהודית, לחלוק על הסמכות המקודשת של גדול הוא כאילו להתווכח עם הקב"ה עצמו.

אלא שה"חסידים" של ה"גדולים" הם אכן עובדי אלילים!

דרך עבודה

 מה היא דרך העבודה של האלילים האלו? עובדיהם אינם מתפללים להם (אלא אם מחשיבים בקשת ברכה מן האדמו"ר כ"תפילה"). אצל חסידים, עבודת האדמו"ר היא הפולחן החסידי של האדמו"ר, למשל, ה"טיש" של האדמו"ר. אצל שאר החרדים, דרך עבודת ה"גדולים" היא הסירוב לבקר אותם או להטיל ספק על יכולתם להכריע בכל תחומי החיים.

(הוספה ב-22/4/19) לאור העובדה שעבודת הרבנים של החרדים מקבילה לעבודת רודנים כמו החטלר, סטלין ומאו, זה כדאי לקרוא לדת החרדים "יהדות טוטליטרי".

(הוספה ב-6/10/19) המאמר הזה (באנגלית) מציע שורש אפשרי ל"דעת תורה": הבנה שגויה למדרש האומרת שהקב"ה הביט בתורה וברא את העולם.

Why are they Blaming Al-Ghazali for the Decline of Moslem Science?

Here is a strange YouTube video of  part of the first day's session from this conference. Steven Weinberg blames this man for Islamic civilization turning against the very idea of natural laws. Neil DeGrasse Tyson quotes him as saying that "mathematics is the work of the devil".

Weinberg's specific example of Al-Ghazali dissing the very idea of natural law is the following, which I quote from here:

Discussing the example that when fire touches a ball of cotton it causes it to combust, Al-Ghazâlî writes about the First Position that the fire alone causes combustion:

This [position] is one of those that we deny. Rather we say that the efficient cause (fâ’il) of the combustion through the creation of blackness in the cotton and through causing the separation of its parts and turning it into coal or ashes is God—either through the mediation of the angels or without mediation.

In other words, cotton is carbonized by fire because Allah wants cotton to be carbonized by fire.

It should have occurred to Weinberg that maybe Al-Ghazali is stating his own version of the Problem of Induction along with his solution to the problem. Just because something has always happened, there is no purely logical reason to expect it to keep on happening. Al-Ghazali's solution is that Allah prefers a universe that is not capricious (or, if you want to allow for miracles, a universe that is almost never capricious). You don't even have to be a theist to propose the problem. Here is how Bertrand Russell the agnostic stated the problem:

The man who has fed the chicken every day throughout its life at last wrings its neck instead, showing that more refined views as to the uniformity of nature would have been useful to the chicken. 

The Problem of Induction is more of a metaphysical problem than a physical problem. Al-Ghazali had no problem with scientific research. He just viewed it as discovery of Allah's will, rather than discovery of natural law.

I did not succeed in using Google to find out where Al-Gazali said what Tyson said he said about mathematics. Al-Ghazali had no problem with mathematics. His problem seems to have been with non-believing mathematicians. If your cynical neighbor doesn't believe, you can just ignore him. But if your neighbor is also a mathematician who has been trained in logic, you might be misled to think that your neighbor has disproved the existence of Allah as rigorously as he proves mathematical theorems.

I thought I had also seen a YouTube video in which Tyson quotes the cotton carbonization example, but now I can't find it.


Weinberg and Tyson are scientists, not historians, not philosophers, and not theologians, so they probably learned about Al-Ghazali only from tertiary sources like this one.

So why did Islamic science wither? I suspect that the cause was not intellectual, but rather sociological. There was something in Islamic society that led the believers to favor an obscurantist misunderstanding of Al-Ghazali. 

Biblical Evidence for Crypto-Pagans

Over the centuries, when Jews have been forced to convert to other religions (usually Christianity), some of the converts continued to practice Judaism secretly. (If you weren't aware of that, you can start making up the deficit in your knowledge by reading this Wikipedia article.)

What is less widely appreciated is that in Biblical times there were crypto-pagans among the Jews.

The clearest Biblical evidence for this is the Book of Esther. The idea that the story of Esther is a pagan story is not new. God doesn't appear in the story at all, and the names "Mordecai" and "Esther" have uncanny resemblances to the names of the two main gods of the Babylonian pantheon, Marduk and Ishtar.

Here is my conjecture. (It may not be original, but I haven't seen it on Google.) In early second Temple times there was a group of Jews who secretly worshiped the Babylonian gods. They preserved their myths of Marduk and Ishtar in a disguised form as a story about two Jews named Mordecai and Esther. Every Adar 14th they had a carnival-style party. When their neighbors inquired, they told them their tradition of the Purim story. The neighbors thought that was a cool idea and joined the celebration, and the idea spread.

The other Biblical story with pagan roots is the story, in the Book of Judges, of Samson. The Book of Judges reads like somebody in late first Temple times collected all the stories he could find about the era of the Judges and wrote them down to promote his agenda, that life under the Monarchy was better than the anarchy that had preceded it. Hence the recurring refrain,

In those days there was no king in Israel; every man did that which was right in his own eyes.

The story of Samson is tacked on towards the end, just for the sake of completeness. Like the story of Esther, the story of Samson looks very much like disguised pagan mythology, invented by a group of crypto-pagans to shelter themselves from persecution, starting with the name "Samson" ("Shimshon" in Hebrew, from "Shemesh" = Sun) and his miraculous birth. What the real meaning of the stories is is necessarily conjectural. One interpretation that I saw a long time ago, is here. There is another one here.

Update on Samson 31/1/22

 The Samson story includes an episode in which he tied burning torches to the tails of 300 foxes to burn down Phillistine crops, as an act of revenge. Recently I found out about something that took place during the Roman Cerealia festival. They used to tie burning torches to the tails of foxes and then release the foxes in the Circus Maximus. There has got to be some kind of connection there.

Bavli Rosh Hashanah 20b II

חכמת מנוח, which is among the commentaries in my Shas following masekhet Rosh Hashanah, pointed me to a book called Yesod Olam, by  Yitzhak ben Yosef Yisreli, whom the first edition of Encyclopedia Judaica calls "ISRAELI, ISAAC BEN JOSEPH". He was a medieval astronomer who wrote the book, at the request of the RoSH, to elucidate the astronomical basis of the Jewish calendar. Section 4 Chapter 8 presents his interpretation of the sugya.

Unlike the medieval commentators in part I, he is not interested in a dateline. I presume that this is because, according to his understanding of geography, all of the inhabitable land surface of the Earth is in what we now would call the "eastern hemisphere", with the rest of the globe being covered by water. So as far as he is concerned, the dateline can be anywhere in the western hemisphere and it doesn't matter where.

Instead, his interpretation is based on three meridians. His prime meridian is about 59 degrees east of Greenwich, which he estimates to be in the middle of the inhabitable hemisphere. His other significant meridians are an east meridian 90 degrees east of the prime meridian, a west meridian 90 degrees west of the prime meridian, and the meridian of Jerusalem, 23.5 degrees west of the prime meridian.

Another factor that he introduces, and that was ignored by the commentators in part I, is that as a real astronomer, he knows that the molad is just an average, and that the actual conjunction of the Sun and the Moon usually is different from the average conjunction by several hours. The modern explanation of this phenomenon is that the Moon's orbit is elliptical. The pre-modern explanation used epicycles. His estimate of the maximum deviation is 14 hours and 648 halakim (one hour = 1080 halakim). 

His explanation of "Differentiate between when the molad occurred before hatzot and when the molad occurred after hatzot" is with reference to noon at the prime meridian, and on the assumptions that the new moon is visible starting 22.5 hours after the true conjunction and that such a thin crescent won't be visible until 20 minutes after sunset. If the molad occurs before noon at the prime meridian, then, if this time the true conjunction was as early as it possibly can be relative to the molad, then theoretically it is possible for witnesses to see the new moon at sunset in or near Jerusalem. If the molad occurs after noon at the prime meridian then it is physically impossible to see the new moon at sunset in or near Jerusalem and witnesses who claim to have done so are mistaken.

This is how he gets it:
6 hours from noon to sunset +
20 minutes = 360 halakim +
Jerusalem is 1 hour and 612 halakim later than the prime meridian (his estimate of the longitude of Jerusalem is 23.5 degrees west of the prime meridian) +
14 hours and 648  halakim is the most time by which the true conjunction can ever precede the molad
= 22.5 hours.

His explanation of "it is necessary that both the night and the day be of the new month" is that that statement of Rabbi Zeira has nothing to do with whether the molad is before or after hatzot at the prime meridian. Instead, it is a rule of thumb to use in the diaspora to estimate when the Sanhedrin declares the new month. If the molad is before local sunset then most likely the Sanhedrin will declare the new month one day later. Otherwise, most likely the Sanhedrin will declare the new month two days later.

In his first explanation of "For us, in Babylonia, it is not visible for six hours of the old moon and eighteen hours of the new; for them, in Eretz Yisrael, it is not visible for six hours of the new moon and eighteen hours of the old" he posits, like the other Rishonim in part I, that "us" doesn't mean Babylonians, and, like some of the Rishonim (Tashbetz second explanation and Ra'avad), that "them" doesn't mean Israelis. Instead, "us" means observers at the east meridian and "them" means observers at the west meridian. He assumes that the Moon is invisible for 48 hours on the average, and gives an example of the true conjunction being at the start of Shabbat (at sunset) near the Fall equinox (for determining the day of Rosh HaShanah). The same time is midnight Shabbat for "us" and noon Friday for "them". The old Moon is invisible all of Friday and the new moon is invisible all of Shabbat at the prime meridian. For "us", though, the first six hours of Shabbat are the last six hours of the old Moon's invisibility and the last 18 hours of Shabbat are the first 18 hours of the new Moon's invisibility. Similarly, for "them", the first 18 hours of Friday are the last 18 hours of the old Moon's invisibility and the last six hours of Friday are the first six hours of the new Moon's invisibility.

I have two objections to Yitzhak ben Yosef Israeli's explanation of the sugya. My first objection is that he disconnects Rabbi Zeira's first statement ("it is necessary that both the night and the day be of the new month") from the baraita quoted by Abba the father of Rabbi Simlai. It is clear from the sugya that Rabbi Zeira's first statement is intended as an explanation of the baraita. My second objection is that the plain meaning of "us" is Babylonians and the plain meaning of "them" is Israelis. It should not be necessary to make "us" mean observers in the extreme east and to make "them" mean observers in the extreme west.

He also has a second explanation of "For us, in Babylonia, it is not visible for six hours of the old moon and eighteen hours of the new; for them, in Eretz Yisrael, it is not visible for six hours of the new moon and eighteen hours of the old" that seems to be based on interpreting "old" as meaning the old month (Elul) and "new" as meaning the new month (Tishrei) but I was unable to make sense of it.

Finally, in part I, my own explanation of "For us, in Babylonia, it is not visible for six hours of the old moon and eighteen hours of the new; for them, in Eretz Yisrael, it is not visible for six hours of the new moon and eighteen hours of the old" was that it refers to a 24 hour discrepancy, between when Israelis see the new moon and when Babylonians see the new moon, that happens in about one out of every 36 months. I was assuming that the difference in longitude between Babylonia and Jerusalem is about 10 degrees. In Section 2 Chapter 3, Yitzhak ben Yosef Yisraeli gives a value for the longitude of Babylonia that places it 13.5 degrees east of Jerusalem, not 10 degrees east of Jerusalem. If I use that longitude difference in my calculation then I get a slightly larger discrepancy frequency of about three times every 80 months.

Christianity's Dirty Secret

When Paul returned to Jerusalem after having spread Christianity among the Gentiles, some of the local Christians jumped on him for requiring Gentile converts just to obey the seven Noahide laws and accept Jesus Christ as their lord and savior, without having to convert to Judaism. Peter defended him (Acts 15:10) in part as follows:

Now then, why do you try to test God by putting on the necks of Gentiles a yoke that neither we nor our ancestors have been able to bear?

In other words, the first Christians, who started out as Jews, were motivated by a desire to get out from under the burden of the 613 commandments. This despite Jesus' own message, in the Sermon on the Mount (Matthew 5:18) that his followers still were bound by Halakha, and later (Matthew 23:2-3) that if you want to know the Halakha, ask the Pharisees.

The irony is that Jesus placed a much heavier burden on his followers. The Sermon on the Mount, by deeming sinful thoughts to be just as evil as sinful deeds, sets the bar too high:

Matthew 5:21-22:

You have heard that it was said to the people long ago, ‘You shall not murder, and anyone who murders will be subject to judgment.’ But I tell you that anyone who is angry with a brother or sister will be subject to judgment.

Matthew 5:27-28:

You have heard that it was said, ‘You shall not commit adultery.’ But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart.

 

Bavli Rosh HaShanah 20b

About 30 years ago I was the leader of a gemara sheur in Houston TX, going through masekhet Rosh Hashanah with Rashi. On daf 20b, as pointed out by Tosafot, Rashi's explanation is contrary to physical reality (I managed to explain Rashi by assuming a flat Earth, putting the Moon at an altitude of about 125 miles, and putting the Sun at an altitude of about 35,000 miles), so I devised my own explanation.

Here is the sugya:

אמר שמואל יכילנא לתקוני לכולה גולה אמר ליה אבא אבוה דרבי שמלאי לשמואל ידע מר האי מילתא דתניא בסוד העיבור נולד קודם חצות או נולד אחר חצות א"ל לא אמר ליה מדהא לא ידע מר איכא מילי אחרנייתא דלא ידע מר כי סליק רבי זירא שלח להו צריך שיהא לילה ויום מן החדש וזו שאמר אבא אבוה דר' שמלאי מחשבין את תולדתו נולד קודם חצות בידוע שנראה סמוך לשקיעת החמה לא נולד קודם חצות בידוע שלא נראה סמוך לשקיעת החמה למאי נפקא מינה אמר רב אשי לאכחושי סהדי אמר רבי זירא אמר רב נחמן כ"ד שעי מכסי סיהרא לדידן שית מעתיקא ותמני סרי מחדתא לדידהו שית מחדתא ותמני סרי מעתיקא למאי נפקא מינה אמר רב אשי לאכחושי סהדי

 Here is a translation to English, from Sefaria, except that:

1.  I changed "midday" to "hatzot", which is what it says in the original (חצות). "Hatzot" can mean either midday (noon) or midnight.
2.  I crossed out the parts of the interpolated explanation that assume that "hatzot" means "midday".

Shmuel said: I am able to fix the calendar for the entire Diaspora without witnesses. Shmuel was an expert on the movement of the celestial bodies and on the principles governing leap years and additional days added to months.

Abba, the father of Rabbi Simlai, said to Shmuel: Does the Master know the meaning of this statement, as it is taught in a baraita dealing with the secret of addition, which discusses calendric calculations: Differentiate between when the molad occurred before hatzot and when the molad occurred after hatzot? He said to him: No, I do not know what this means. He said to him: Since the Master does not know this, there are probably other matters that the Master does not know, and therefore you must not establish a calendar, relying upon calculations that were made based on faulty or insufficient knowledge.

As for the meaning of this obscure baraita, when Rabbi Zeira went up from Babylonia to Eretz Yisrael, he sent back a letter to his colleagues in Babylonia: In order for a day to be sanctified as the New Moon, it is necessary that both the night and the day be of the new month. That is to say, the molad must occur before the beginning of the night.

And this is what Abba, the father of Rabbi Simlai, said: The baraita means as follows: They calculate the molad; if the molad occurred before hatzot, so that there are at least six more hours left of the day, it is known that the moon will be visible close to sunset. If, however, the molad did not occur before hatzot, so that there are fewer than six hours left of the day, it is known that the moon will not be visible close to sunset.

The Gemara asks: What is the practical difference that this statement makes? In any case, the court is dependent upon the testimony of witnesses. Rav Ashi said: This information is used to refute the witnesses, as if the witnesses claim that they saw the new moon at a time when it was not visible according to the calculations, they are clearly false witnesses.

Rabbi Zeira said that Rav Naḥman said: For twenty-four hours the moon is covered, i.e., not visible. This occurs between the last sighting of the old moon and the first sighting of the new moon. For us, in Babylonia, it is not visible for six hours of the old moon and eighteen hours of the new; for them, in Eretz Yisrael, it is not visible for six hours of the new moon and eighteen hours of the old.

The Gemara asks: What is the practical difference that this statement makes? Rav Ashi said: It is used to refute the witnesses, as if they testify that they saw two moons, the old and the new, within a single twenty-four hour period, they are certainly false witnesses.

 I also crossed out "faulty or" because "faulty" is being mean to Shmuel. Abba's point was that the Sanhedrin has criteria in addition to astronomical criteria that might lead it to declare the first day of a new month one or two days different from what a purely astronomical calculation would indicate. As is stated in the mishnah at the top of 25a, a new month starts when the Sanhedrin says it starts, no matter what the Moon is doing.

The baraita is a rule of thumb that the Sanhedrin used to verify testimony about the sighting of the new crescent Moon.

According to Wikipedia the Moon is invisible, around the time of new Moon, for between 1.5 days (36 hours) and 3.5 days (84 hours). If the time from the last possible visibility of the old crescent Moon to the first possible visibility of the new crescent Moon is 36 hours then the time from the molad to the first possible visibility of the new crescent Moon is half of 36 hours, i.e., 18 hours. Then the hatzot in the baraita can't be noon on the day that the new crescent Moon will be visible at sunset, because the new crescent moon won't be visible until sunset of the following day. The next candidate for hatzot-hood is the preceding midnight. If the baraita is based on the assumption that the new Moon is invisible for 36 hours, then the rule of thumb makes sense. If the molad is before midnight then the time to the next sunset is more than 36/2=18 hours and the new crescent moon will be visible. If the molad is after midnight then the time to the next sunset is less than 18 hours and the new crescent moon won't be visible. "The night and the day being of the new month" means "most of the night, plus the following day, are after the molad.

That explains the baraita. We still need an explanation of Rav Nahman's statement. Rav Nahman can't really mean that the new Moon is invisible for 24 hours because that invalidates the baraita. If the new Moon is invisible for 24 hours then the time to which the molad should be compared is sunrise (24/2=12 hours before sunset), not noon or midnight.

The explanation I gave in Houston was that Rav Nahman's 24 hours is a possible discrepancy between observations of the first new crescent Moon (and also the last old crescent Moon) in Babylonia vs. Eretz Yisrael. Usually, observers in Babylonia and in Eretz Yisrael see the last old crescent Moon at sunrise on the same day, and see the first new crescent Moon at sunset on the same day. About 1/36th of the time, the last observation of the old crescent Moon is a day earlier in Eretz Yisrael than in Babylonia, and the first observation of the new crescent Moon is a day earlier in Eretz Yisrael than in Babylonia. Rav Nahman's point is that, in addition to knowing all the Sanhedrin's criteria for declaring the first day of a new month, someone who wants to predict the calendar needs to be aware of the possibility of observational discrepancies between Babylonia and Eretz Yisrael.
The longitude of Jerusalem is 35.2 degrees east. The longitude of Baghdad is 44.4 degrees east. So the difference in longitude between Babylonia and Eretz Yisrael is about 10 degrees, and the time in Eretz Yisrael is about 40 minutes behind the time in Babylonia.

For simplicity, suppose that the molad is at midnight halfway between Babylonia and Eretz Yisrael. Then the molad is at 00:20 in Babylonia and at 23:40 in Eretz Yisrael. Also for simplicity, suppose that sunrise in both places is at 06:00 and that sunset in both places is at 18:00. The sunrise immediately before the molad was 18 hours and 20 minutes before the molad in Babylonia and 17 hours and 40 minutes before the molad in Eretz Yisrael, so the old crescent Moon was still visible in Babylonia but no longer visible in Eretz Yisrael. The sunset immediately after the molad will be 17 hours and 40 minutes after the molad in Babylonia and 18 hours and 20 minutes after the molad in Eretz Yisrael, so the new crescent Moon will be visible in Eretz Yisrael but not yet in Babylonia.
Rav Nahman's description of the 24 hour delay before the new crescent Moon is visible in Babylonia is the 18 hours of the "new moon" from the molad until the next sunset, when the new crescent Moon is not yet visible, plus the 6 hours of the "old moon" back to the previous sunset. His description of the 24 hour pause in the visibility of the old crescent Moon in Eretz Yisrael is the 18 hours of the "old moon" from the last sunrise before the molad, when the old crescent moon was no longer visible, until the molad, plus the 6 hours of the "new" moon from the molad until the next sunrise.

30 years ago I had neither the time nor the ability to look for classical explanations of the sugya other than Rashi's, but I had heard that the sugya was somehow connected to the definition of the halakhic dateline. Now I am retired and there is Internet. At HebrewBooks.org I found the book ישועות כהן - קו התאריך. Chapters 3-6 of that book explain the ways that four Rishonim (the Kuzari, HaRav Zerahya Halevi (Ba'al HaMaor), Rabbi Shimon ben Tzemah Duran (the Tashbetz) and Ra'avad) get the dateline from our sugya. All four systems are problematic. All four Rishonim agree that the dateline is 90 degrees east of Jerusalem, but to do that they need to define "us" as observers at or near the dateline, not in Babylonia. In addition, their values for the time that the new Moon is invisible (48 hours for Kuzari, Ba'al HaMaor and two of Tashbetz' three explanations, 24 hours for Tashbetz' third explanation, and 12 hours for Ra'avad) are inconsistent with the baraita.

 While writing the above, another explanation of Rav Nahman occurred to me. Rav Nahman accepts at face value the reading of the baraita as saying that the new crescent Moon might be visible in Eretz Yisrael at sunset if the molad is before noon, but he knows from his own observations that the new crescent Moon isn't visible in Babylonia until 18 hours after the molad. His conclusion is that the new Moon is invisible for 24 hours, but for some reason those 24 hours are partitioned differently around the molad in Eretz Yisrael than in Babylonia.

Under either explanation of Rav Nahman, what his statement has to do with verifying testimony about sighting the new crescent Moon is: be careful about using astronomical data from Babylonia to invalidate testimony about sightings in Eretz Yisrael.