Wednesday, March 29, 2006

Rosh Chodesh Nisan

We missed it in the United States, but elsewhere in the world (particularly North Africa and the Middle East) they saw a total solar eclipse today. Thus, today was the new moon, the time when the moon is directly between the earth and the sun. (Of course, not every month has a solar eclipse.) According to our mathematical algorithm, tonight is Rosh Chodesh Nisan. In a nod to the old days when the new month was declared based on testimony of witnesses, Rosh Chodesh may be observed on or after the date of the molad (lunar conjunction), but never before. In fact, if the molad occurs any time after noon, then Rosh Chodesh must be delayed to the next day, because it takes 6 hours from the conjunction until the crescent moon is visible (according to Rosh Hashanah 20b).

Back in the day, would the Sanhedrin have accepted testimony about a total solar eclipse as evidence of the new moon? If so, then it wouldn't be necessary to wait 6 hours. Sadly, I'm almost certain that the answer is no, given all the sources that talk about the shape of the crescent moon and such.

It's strange. The rabbis were certainly aware of eclipses (Sukkah 29a has some bubbe meises for solar and lunar eclipses), and were certainly aware of the phases of the moon (duh), but I've seen no evidence that they were aware that eclipses are linked to the phases of the moon (solar eclipses always occur at the new moon, and lunar eclipses at the full moon). Counterexamples, anyone?

Happy New Year! According to Rosh Hashanah 1:1, the 1st of Nisan (tonight) is the new year for kings and festivals.

Kings: On official documents, years were identified as "the nth year of King ____". This number was incremented on 1 Nisan, regardless of when the king took office. For example, in the United States, the 1st year of King George lasted from 20 January 2001 to 1 Nisan 5761. (Actually, any time from 1 Nisan 5760 to 1 Nisan 5761 could be referred to as either "the 9th year of King Bill" or "the 1st year of King George".) The 2nd year of King George was from 1 Nisan 5761 to 2 Nisan 5762. We just finished the 6th year, and are starting the 7th (and antepenultimate, baruch hashem) year of King George.

Festivals: Deuteronomy 23:22 says that if you vow to bring an offering, don't procrastinate! There are different opinions in the Gemara about exactly what the time limit is before you're in violation of bal t'acheir (don't be late). One opinion is that you have one full festival cycle to get everything in, and that cycle begins in Nisan, with Pesach.

But that's not all! Rosh Hashanah 7a says that the 1st of Nisan is also the new year for months, leap years, shekalim, and (some say) renting houses.

Months: Nisan is "the first month", even though the years are incremented in Tishrei (the seventh month).

Leap years: If you didn't add an extra month (Adar) to make the year a leap year, then once the 1st of Nisan rolls around, you've missed your chance.

Shekalim: The 1st of Nisan is the beginning of the fiscal year in regard to the shekel donations to the Temple. The offerings for this year have to be bought out of the shekalim from this year, and the 1st of Nisan is when that flips over.

Renting houses: If a lease says "for this year" (rather than "for one year" or "for 12 months"), then the lease goes until the 1st of Nisan.


  1. Joe in AustraliaMarch 30, 2006 6:04 AM

    Some rabbonim were competent astronomers, and it's inconceivable that they didn't know that eclipses are linked to the molad. It's not only the sort of thing that's very obvious to someone following the course of the moon, but I believe it's explicitly stated by astronomical books of the time.

  2. any plans to write a nigun for this rosh chodesh after the smashing success of rosh chodesh sivan ?

  3. "Deuteronomy 23:22 says that if you vow to bring an offering, don't procrastinate! [snip] One opinion is that you have one full festival cycle to get everything in, and that cycle begins in Nisan, with Pesach."

    This is ridiculously trivial, but my first thought was that proper etiquette concerning wedding gifts (i.e., that one has a year after the wedding to send a gift) is quite similar!


  5. Oh yeah, and it just occurred to me - by definition, you don't see the new moon at an eclipse. You see it's silhouette, which is not the same thing. An eclipse is actually the time when it's *hardest* to see the moon, when it's in the sky.

  6. According to the Midrash and Tosefot Rosh HaShanah 8b, Adam HaRishon, got the Tsivui to be Mekadesh HaLevana at the 21th hour, the Molad having been at the 14th hour. How could he have observed the Moon, even after six hours? It was still day! A possible answer: he did not observe the mood, but he had observed the Molad. How? He saw a solar eclipse at hour 14! According to the Midrash, the Moon and the Sun were fighting for hegemony. I nice description of a solar eclipse, no?

    Moshe Lerman,

  7. adina's dadApril 17, 2006 8:48 PM

    The reason for the minimum 6 hours between molad and Rosh Chodesh is not because the moon cannot be viewed until 6 hours after the molad. It is because the molad, which is the mean new moon, can vary by a few hours from the ibbur, the actual new moon (i.e. the moment when the moon passes the sun in the sky). This is because the apparent speed of the sun around the ecliptic varies during the year, due to the eccentricity of the earth's orbit around the sun, and because the apparent speed of the moon through the sky varies, due to the eccentricity of the moon's orbit around the earth. I don't think it can be off by as much as 6 hours, I think the most it can be off is something like 3 hours, but maybe they weren't sure and wanted to play it safe.

    The minimum time from the ibbur until the new moon is visible to the naked eye is much longer than 6 hours. I think the record is something like 11 hours, and the average minimum time is about 15 hours. Since the criterion for eidim seems to be actually seeing the lit up crescent moon, not just knowing that the ibbur has already occurred from seeing an eclipse, Rosh Chodesh according to the fixed calendar actually can occur earlier than it would if we relied on eidim. Apparently that did not bother Hillel Sheni, as long as Rosh Chodesh could not start before the ibbur.