Literary critic Adam Kirsch is reading a page of Talmud a day, along with Jews around the world.How often does a modern city-dweller think about the moon? Could you tell, without looking it up, what phase the moon is in tonight, or where it will appear in the sky at any given hour? Probably not, and why would you—for many of us today, the moon is just a big decoration in the sky, and the destination of some old Apollo missions. For the rabbis of the Talmud, however, the moon was the key to the whole rhythm of Jewish life. Because the Jewish calendar is a lunar calendar, with the beginning of the month tied to the appearance of the waxing crescent moon, the whole rabbinic and priestly establishment was highly attuned to the moon’s phases and trajectories. This week’s Daf Yomi reading, which included the end of Chapter 1 and all of the brief Chapter 2 of Tractate Rosh Hashanah, was all about the procedures for determining exactly when the waxing crescent moon appears.Like most educated people in the ancient and medieval worlds, the rabbis of the Talmud had a sophisticated knowledge of astronomy. (Just read Dante or Chaucer to see how well a literate person was expected to know the cycles of the moon and the constellations.) This knowledge was, of course, based on a fundamental error about the solar system—they didn’t know the Earth revolved around the sun—but when it came to charting the appearance of the moon in the sky, they were experts. It was well within their competence, then, to figure out the lunar calendar in advance. The rabbis could calculate which months would contain 29 days and which 30 days, and which years would need an extra month added to keep the solar and lunar calendars in alignment. Indeed, in Rosh Hashanah 20b, Shmuel declares rather vainly, “I am able to fix the calendar for the entire Diaspora without witnesses.”To avoid any possibility of error, however, the traditional practice, dating to Temple times and even earlier, was to certify the arrival of the new month by asking witnesses to testify that they had actually seen the waxing crescent moon appear in the sky. The Talmud explains that, while the Temple stood, there was a special priestly court devoted to hearing witnesses about the moon. “There was a large courtyard in Jerusalem which was called Beit Ya’zek,” we read in Rosh Hashanah 23b. “And there all the witnesses would gather and the court would examine them there. And they would prepare great feasts for them, so that they would be willing and accustomed to coming.”Testifying before this court was an important mitzvah—so much so that it was even permitted to violate Shabbat in order to travel to Jerusalem and give testimony. People traveling for this purpose could walk beyond the usual Shabbat boundary and even carry weapons for self-defense. (This last provision says something about the state of law and order in Second Temple-era Judea.) In Jewish law, it takes two independent witnesses to confirm any statement in court, so Jews would come to the Temple in pairs to testify. On one occasion, the Talmud says, as many as 40 pairs of people showed up to say they had seen the waxing crescent moon. Since only one pair was really needed, Rabbi Akiva was going to send the rest home, but Rabban Gamliel stopped him: If he started discouraging people from testifying, Gamliel worried, a day might come when nobody showed up at all. Better too many witnesses than too few.Still, the Talmud explains that not everyone is allowed to testify about the moon. Family members cannot support one another’s testimony; a father and son, for instance, cannot serve as two separate witnesses. And people of low moral character can’t testify at all: This includes professional gamblers (“one who plays with dice”), pigeon racers, merchants who sell illegal produce, and people who lend money at interest. Furthermore, witnesses had to be personally known to the members of the court, or else they had to be vouched for by someone who was.This precaution was introduced on account of the Boethusians, a schismatic Jewish sect that had its own ideas about how the calendar was supposed to be calculated. (It was very important to them, for instance, that Shavuot always fall on a Sunday, due to their idiosyncratic reading of a particular verse from Leviticus.) In order to get the calendar to follow their rules, they would sometimes give false testimony about the waxing crescent moon in order to have the new month declared at the wrong time. Indeed, in Rosh Hashanah 22b, we read about how the Boethusians once bribed a man 200 dinars to claim he had seen the waxing crescent moon when he hadn’t. Fortunately, the man was a loyal Pharisee—an adherent of the mainstream rabbinic tradition—and he told the court what had happened: “I heard that the Boethusians were seeking to mislead the sages,” he explained, “and I said to myself; I will go and hire myself out to give false testimony, and I will inform the sages of the truth, lest unworthy people come and mislead the sages.”Once the new moon was certified and the new month announced, it was necessary for the authorities in Jerusalem to spread the news throughout the Jewish world. This was done through a system of torch relays: A messenger would light a torch on top of a mountain, “and wave it back and forth and up and down, until he would see his colleague doing likewise on the top of the second mountain,” and so on. Unlikely as it seems, the Talmud claims that an unbroken chain of such torches carried the news all the way from Judea to Babylonia, which is modern-day Iraq, a distance of hundreds of miles. After the last relay, the final messenger “would see the entire Diaspora before him alight like one large bonfire,” a breathtaking image of the whole Jewish people signaling with their torches across the world.Yet the rabbis realize that this sounds a little too good to be true: “What is ‘Diaspora’?” they ask, knowing that it would be impossible to see all Jews, everywhere, from a single mountaintop. In this case, Rav Yosef explains, “Diaspora” is referring simply to the city of Pumbedita, a major Jewish community in Babylonia; apparently, “each and every individual [in the city] would take a torch in his hand and ascend to the top of his roof.” In this way, the Jewish calendar would be synchronized in the two major centers of Jewish civilization.In the course of this discussion, the rabbis make an unexpected swerve into the subject of forbidden images. According to the mishna in Rosh Hashanah 24a, Rabban Gamliel, the leading sage of his time, had a diagram of the phases of the moon hanging in his attic, which he would use to help witnesses describe exactly what they had seen in the night sky: “And he would say to them: Did you see a form like this or like this?” Evidently Rabban Gamliel found nothing wrong with this, but the Gemara instantly raises a challenge based on Exodus 20:19: “You shall not make with me gods of silver, or gods of gold.” To the rabbis, “gods” means “attendants of God,” that is, the celestial bodies of sun and moon. Does Rabban Gamliel’s chart violate this prohibition?To answer this question, the rabbis must figure out exactly what the ban on graven images is meant to accomplish. Abaye holds that the Torah only prohibits making exact reproductions of holy things: That is why it’s forbidden to make a seven-branched candelabrum, which would be an imitation of the candelabrum in the Temple. But since the moon can’t be reproduced, only represented, it’s all right to make a picture of it. The Gemara counters Abaye’s view, wondering why, in that case, it’s not permitted to make an image of a human face—after all, a face is not a whole person. But here, Abaye holds, there’s another reason for the prohibition: Because human beings are made in God’s image, any picture of a human being is an image of an image of God, and so it is forbidden.In the end, however, the rabbis reject Abaye’s argument about the moon, holding that any representation of a celestial body is indeed prohibited. But surely it’s inconceivable that a sage as holy as Rabban Gamliel would have violated this commandment; so how do we explain his lunar diagram? Could it be that it is allowed because he did not make it himself, but had a gentile make it for him? No, the Gemara decides, that wouldn’t be an excuse, since even possessing a forbidden image is a violation of the law. Finally, the rabbis come up with a satisfying answer: Images are forbidden for purposes of decoration, but for the purpose of Torah study they are allowed. “You may learn to understand and to teach,” the Gemara concludes. As so often happens in the Talmud, study proves to be the highest Jewish value of all.***To read Tablet’s complete archive of Daf Yomi Talmud study,click here.Adam Kirsch is a poet and literary critic, whose books include The People and the Books: 18 Classics of Jewish Literature.