Rosh Hashanah 24

Rabban Gamliel’s moon chart.

Advertising on my social media feed suggests that it would be fun and trendy for me to hang a personalized star chart on my wall — presumably to gaze every day at the stars’ alignment on the date that my husband and I got married, or my children’s birth dates or some other momentous occasion. I have been tempted, and I was intrigued to discover that Rabban Gamliel also had some astronomical décor in his upstairs room, as our mishnah teaches:

Rabban Gamliel had a diagram of the different forms of the moon drawn on a tablet that hung on the wall of his attic, which he would show to the laymen (who came to testify about the new moon). And he would say to them: Did you see a form like this or like this?

The new moon is not, as some suppose, a lack of a moon in the sky, but the first tiny sliver of moon that is visible after the last month’s moon has truly disappeared. And this is why identifying it can be confusing. How do you know if you are looking at the last tiny sliver of the old moon, or the first tiny sliver of the new one? The answer is in which direction it faces. If it looks like a C, open on the right, then it is the old moon. If it is curved like a backwards C, open on the left, then it is the new moon. Likely, Rabban Gamliel used his moon charts to check whether or not witnesses had seen a moon that faced the correct direction.

Though the use of this chart was practical, the other sages were concerned that having this chart was a violation of Jewish law. As the Gemara immediately remarks:

​​And is it permitted (to hang a moon chart)? Isn’t it written: “You shall not make with me gods of silver, or gods of gold” (Exodus 20:20)? Meaning: You shall not make images of my attendants.

The verse cited here, Exodus 20:20, comes right after the recitation of the Ten Commandments and is of a piece with the prohibition on creating a graven image found in Exodus 20:4: “You shall not make for yourself a sculptured image, or any likeness of what is in the heavens above, or on the earth below, or in the waters under the earth.”

The rabbis read Exodus 20:20 to mean that it is not just making an image of God that is prohibited, but also making an image of any of God’s heavenly attendants — which could be interpreted to include the celestial bodies, among them the moon.

It seems difficult for the rabbis to imagine an image of the moon would not be used for worship. On the other hand, the rabbis wonder, perhaps as the nasi, the head of the community, Rabban Gamliel can be trusted to use the moon images correctly and is permitted behaviors that might be forbidden to others. They argue this back and forth down our page.

Often the rabbis let disagreements stand unresolved, but in this case they manage to agree on a compromise  — one that has repercussions for Jewish practice today:

If you wish, say that Rabban Gamliel did this to teach himself, as it is written: “You shall not learn to do after the abominations of those nations”  (Deuteronomy 18:9), which indicates: However, you may learn to understand and to teach. 

The strange language of Deuteronomy 18:9, that one should not “learn” to commit abominations (like idolatry), suggests to the midrashic mind that one may “learn” in order to serve God. In other words, it is permitted to do certain things that would otherwise be prohibited — like decorate one’s attic with moon charts — for the sake of Torah study and divine service.

L’shem hinuch — for the purpose of education — is a principle to which we turn today. Can we say the Hanukkah blessings at 9 a.m. in a preschool classroom? Can we say the blessing over matzah at a model seder two weeks before Passover? Can we draw a star chart or the phases of the moon on our wall without concern that it will become an object of idolatrous worship? Yes, say the rabbis, if it is for the purposes of better understanding our traditions and teaching them to others.

Read all of Rosh Hashanah 24 on Sefaria.

This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on November 2nd, 2021. If you are interested in receiving the newsletter, sign up here.

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