Jews around the world will gather at the end of this week on the 15th of Nisan, Friday night April 19, to celebrate the Passover Seder.
In the book of Numbers (28:17) we read, “On the 15th day of this month there is to be a festival; for seven days eat bread made without yeast.” It is commonly understood on the 15th of a Hebrew month there is a full moon, so it is not surprising that many of the full moons of the year are also Jewish holidays: Sukkot, Tu Bishvat, Shushan Purim, Passover, and Tu Be’Av. One of the benefits of a full moon, particularly thousands of years before electricity, is that it provides light throughout the entire night, as the moon rises at sunset, reaches its zenith near midnight and sets at sunrise in the morning.
The text is clear in instructing us that many of the Jewish holidays fall on the 15th of the month, however the text does not say those holidays need to fall when the moon is full. While there is often a full moon on the 15th of the Hebrew month, that is not the case every month!
For example, this past Sukkot, the full moon took place the morning of the 16th of Tishrei, not the 15th of Tishrei, while in two years, (2021/5781), the full moon will appear on the second day of Passover, the 16th of Nisan, not the 15th of Nisan. Technically, a full moon, as well as a new moon, lasts a brief moment when the sun, earth, and moon line up, although to the human eye, the full moon may appear at times to last a day and a half before and after that moment.
How did we get to such a situation? In the beginning of the Torah (Genesis 1:14) we are told, “And God said, ‘Let there be lights in the vault of the sky to separate the day from the night, and let them serve as signs to mark sacred times, days and years.’”
The Hebrew word for sacred times is moadim, from the word moed, which is often associated with the festivals of the Jewish calendar. In fact, the second order of the Mishna is called Moed and discusses the Jewish holidays. In our verse from Genesis, one of the “lights” is the moon, and so the moon from the beginning of the Bible is associated with many of the holidays. But we note it does not refer at all to a full moon.
The only place where we seem to get any association with the full moon and the holidays is in Psalm 81:3 where we are told, “Sound the ram’s horn at the New Moon, and when the moon is full, on the day of our festival.” The Hebrew word used in this Psalm is keseh, which can be understood to mean full moon. The problem is that the word keseh is a hapax legomenon (a word that appears only once in the Bible), so it is difficult to translate. In the Talmud (Rosh Hashanah 8b), we read that keseh means “covered,” and refers not to the full moon, but soon after the new moon; the waxing crescent moon at the beginning of the lunar month in which all but a thin sliver of the moon shows as we mostly see the darkened moon. Nathan Stein suggests that keseh has nothing to do with the moon but rather refers to a round musical instrument. With all of this, we discover the one possible connection to the Jewish holidays falling on the full moon is at best one of a number of different interpretations of a verse from the book of Psalms.
IT IS clear by having so many of the holidays fall on the 15th of the month, there was a hope that they would fall when there would be a full moon, but that was not the explicit commandment.
The first mitzvah (commandment) we are told to perform as a people while we prepare for freedom after slavery is to create a calendar. At that moment, it says (Exodus 12:2), “This month shall mark for you the beginning of the months; it shall be the first of the months of the year for you.” There is a logic to this, since the essence of being free is to have control over how we use our time; something a slave can’t do.
Nonetheless, it is impossible to do this commandment completely correctly. The period from one new moon to the next is called a synodic month, and it is 29.5305889 days long. However, that is not a constant. Around 1900, a synodic month was 29.5305886 days, and in 2100 it will be around 29.5305891 days. We also need to note that these are average numbers. In fact, the physical length of a year may vary by several minutes because of the gravitational force from other planets. In addition, the time between full moons may change by several hours because of fluctuations in the gravitational force from the sun, and the moon’s orbital inclination. The addition of a leap month, Adar Bet, in the calendar of Hillel II (359 CE), which we use to this day is unable to address all of these variables.
Relatedly, this Thursday night, after we have tried to completely clean our homes of hametz (leaven), an impossible task, we will recite, “Any hametz which is in my possession, which I have not seen and I have not destroyed, is hereby nullified and should be considered like the dust of the earth.” That is to say that we do our very best to clean our homes of all of its hametz. With the words of this formula, the tradition recognizes it is impossible to fully carry out. So it is with the 12th chapter of the Book of Exodus, where the commandment to establish a calendar is introduced along with the Passover holiday. As we have examined, that, too, is impossible to do perfectly all of the time.
When our holiday of freedom is introduced, it comes with an important caveat. That is to say, the tradition may set high standards, asking us to do the impossible, and realizes that. What it really demands from us is that we give our best. In a parallel message, Rabbi Tarfon (Mishna Avot 2:16) teaches, “It is not incumbent upon you to finish the task, but neither are you free to absolve yourself from it.”
At the core of the message of Passover is that freedom comes with a demand – that we give our maximum effort in the choices and tasks before us.The writer, a rabbi, teaches at the Arava Institute and Bennington College.