7 out of every 19

Last shabbat we blessed the coming of the new moon of Adar. I shared that this year we are welcoming Adar 1, because it is a Jewish leap year. Unlike the Gregorian calendar which adds a day to the end of February, the Jewish calendar doubles an entire month. This is what allows us to follow the lunar cycles and also stay in rhythm with the solar seasons such that Passover will always be in the spring time. However, when I shared this, I misspoke and said that Jewish leap years happen every four years. That, in fact, is not true. That is when Gregorian leap years happen. The Jewish calendar follows a much more idiosyncratic (or perhaps natural) rhythm. Here is what I learned this week, with huge gratitude to Rachel and Nati Katz Passow for being my teachers.

In the days before the calendar was codified (and climate change was happening), the rabbis would go out into the fields at the end of the month of Shvat (say, around last week) to inspect the barley. According to the biblical calendar, Passover is a barley harvest and so the spring festival must be timed with the crop. If the barley looked like it would be ready six weeks later, it wasn't a leap year. And if it needed more time, it was a leap year. (This is the ancient Hebrew groundhog day!) In this way they were able to align the festivals with both the harvest and the seasons. Put another way, the harvest defined the seasons for them.

In our times, Jewish leap years occur seven out of every 19 years. Which is actually a lot more frequently than Gregorian leap years. Now you might ask, how did they come up with a 19-year cycle. That is hardly a familiar Jewish number. I don't quite know. But somehow, though, the number 19 is at once completely random and naturally attuned. As it turns out, it corresponds to the pattern of the keys on a piano, which are divided into 19 equal temperaments. (You can actually use the spacing of black and white keys to know whether it's a leap year!) Now I am certainly not a music theorist. But while many people call it coincidence, it seems to me there is a resonant echo between the natural world, music, and math that defies logic and alludes to a deeper truth.

In the words of Rami Shapiro, "Nature is God's niggun, a wordless melody of unfolding Life."

But still, how do I know what year it is? The Hebrew Leap Year follows a 19-year cycle. The years of the 19-year cycle that are leap years are: 3, 6, 8, 11, 14, 17, and 19. For the brave of heart, there are amazing mathematical equations that line up with a Hebrew mnemonic (גוחאדז"ט), which you can explore and play with to figure out which year it is. I personally am sticking to Hebcal for this information.

As we begin this first month of Adar, I invite you to marinate in the patient joy it brings as we journey towards the expanse of spring.

Shabbat shalom,
​Rabbi Ari Lev