Five ‘seconds’ too many

We know to the fraction of a second when the next molad — the “birth” of the new moon — will occur over Jerusalem. Indeed, using the fixed calculations of the Jewish calendar, we can determine the exact moment any molad will occur far into the future.

“Molad” literally means birth in Hebrew, and from the days when the Second Temple stood, Jerusalem has served as Jewish time’s “prime meridian” — the fixed reference point from which the Jewish calendar measures sacred time, much as Greenwich serves as the reference point for world time zones. Once we know exactly when a new moon will appear over Jerusalem, we know when a Jewish month ends and a new one begins throughout the Jewish world.

For example: On Thursday evening, September 30, 2027, the molad for the month of Tishrei will occur in Jerusalem precisely at 31 minutes, 46 seconds, and 793 chalakim after 6 p.m. A chelek is 1/1080th of an hour — meaning Jewish tradition calculates the moon’s cycle down to the tiniest fractions of a second.

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The following evening, Friday, October 1, at sunset, the month of Elul will end, Tishrei will begin, and Rosh Hashanah 5788 will commence.

I am writing this on May 24, 2026 — 495 days before that moment arrives — yet we already know to the fraction of a second exactly when it will happen.

Why?

Because the Jewish calendar today is fixed and mathematically precise. Every lunar cycle is calculated according to the same interval: 29 days, 12 hours, and 793 chalakim. Once one molad is known, every future molad can be projected indefinitely.

This, however, raises an uncomfortable question: If we can predict the Jewish calendar centuries in advance, why must Jews in the Diaspora still observe “Yom Tov Sheni Shel Galuyot” — the five additional festival days attached to the first and last days of Pesach and Sukkot, and to the single day of Shavuot, outside the Land of Israel?

The simple answer is: There no longer is a practical reason for it.

The complicated answer is why we continue observing it anyway.

Ask many Jews why the Jewish calendar follows the moon, and the answer usually is: “Because the Torah says so.” Those a bit more knowledgeable will add, “It’s in Exodus 12:2.”

Except the Torah does not actually say that — in Exodus 12:2 or anywhere else. The verse states: “This chodesh shall mark for you the beginning of the chodashim.” We translate chodesh as “month,” but the word actually comes from the Hebrew root for “new.” More literally — albeit awkwardly — the verse reads: “This newness shall mark for you the beginning of the newnesses.”

The Torah appears to picture God showing Moses something new in the sky — most likely the first visible crescent of the moon. Yet the broader context of Exodus 12 points in another direction as well.

The Exodus marks the birth not merely of freedom, but of nationhood. God is effectively telling Moses: From this moment onward, Israel is a nation, not just a confederation of tribes loosely connected by a common ancestor (Jacob). And so, from now on, Israel will count time as nations count time — beginning with its own defining moment.

In the biblical era, months originally were established by actual moon sightings. But Leviticus 23:37 adds another requirement: “These are the set times of the Lord, which you shall proclaim.”

The festivals had to be formally declared, which required that the months had to be proclaimed.

That responsibility belonged to the Sanhedrin in the Second Temple period. Near the expected time of the molad, members of the Sanhedrin would go outside and search the sky for the first visible crescent of the new moon. Witnesses who also claimed to have seen it then appeared before the court, and if their testimony was accepted, the new month was formally proclaimed.

Signals then were sent across the land. A torch was lit on the Mount of Olives. From there, chains of fire spread from hilltop to hilltop, carrying news of the new month to nearby Jewish communities. messengers were dispatched to communities farther away.

But communication was imperfect. Messengers were delayed. Political rulers of Diaspora lands sometimes interfered. Jews outside the Land of Israel often did not know in time which day had officially been declared holy.

That uncertainty gave rise to Yom Tov Sheni Shel Galuyot — the “second festival day of the Diaspora.”

Originally, the practice made complete sense.

Today, however, the uncertainty no longer exists. Long before the Sanhedrin ceased functioning, Jewish authorities already relied heavily on astronomical calculation. The Babylonian Talmud itself refers to a fixed calendar system (Beitza 4b). By the medieval period, Sefer HaChinuch could state that “all of Israel had become expert in fixing the month.”

The 4th-century calendar associated with Hillel II was tweaked a bit over time, but it eventually became universal.

The requirement that the new month be formally proclaimed did not disappear with the Sanhedrin. Instead, it became part of synagogue ritual through the blessing of the new month on the Shabbat before Rosh Chodesh. On the Shabbat before Rosh Hashanah 5788, for example, congregations around the world will announce that the molad over Jerusalem will occur on Thursday evening at precisely 31 minutes, 46 seconds, and 793 chalakim after 6 p.m.

We announce it before it happens. We know exactly when it will happen.And yet we still behave as though uncertainty remains.

The standard justification for this is simple: “This is how Jews have done it for nearly 2,000 years.” More formally, the Talmud insists on this by saying that minhag avoteinu b’yadeinu — “the custom of our ancestors is in our hands.” (See the Babylonian Talmud tractate [BT] Beitzah 4b.)

Tradition matters deeply. But Jewish law never treated precedent alone as untouchable. A sharp medieval quip, often attributed to Rashi’s famed grandson and Tosafist extraordinaire Rabbeinu Tam, notes that when minhag (spelled mem-nun-hey-gimmel) is spelled backwards, it spells Gehinnom — the rabbinic euphemism for hell.

Rabbeinu Tam was no enemy of custom. Quite the opposite; he was a staunch defender of minhag. His point was that custom becomes dangerous when inherited practice is treated as untouchable after people no longer remember why it began, whether its original conditions still exist, or whether it still serves Torah’s larger goals.

Judaism needs continuity, to be sure, but continuity can become rigidity, and rigidity can eventually alienate the very people tradition is meant to sustain. Ironically, even Rabbenu Tam — often portrayed as a strong traditionalist — understood that danger.

Maimonides, the Rambam, also understood that danger. He writes that rabbinic authorities may alter even long-established practices “to restore the people to the faith” or “to save many Jews from becoming lax in observance.” Halachic leaders, he insists, must “act as the needs of the time require” (Mishneh Torah [MT] Mamrim 2:4–5).

And the needs of the time are becoming impossible to ignore.

Survey after survey shows that large numbers of American Jews increasingly feel disconnected from normative Jewish observance altogether. The problem is not simply ignorance. Many Jews experience religious practice as increasingly burdensome, rigid, and inaccessible.

Not every stringency strengthens Judaism. Sometimes it weakens it.

The Talmud itself recognizes the principle of tirchah d’tzibbura — imposing excessive burdens on the community. In BT B’rachot 12b, our Sages of Blessed Memory rejected adding an additional yet somewhat longish paragraph to the three paragraphs of the Shema because it would overburden worshippers.

If a few extra minutes mattered to the Sages, should an unnecessary additional festival day not matter to us?

The issue ultimately is larger than calendar mechanics. The real question is whether Judaism knows how to distinguish between preserving tradition and preserving Jews.

Yom Tov Sheni once solved a genuine problem. That problem no longer exists. But another problem does.

And unless we are willing to confront it honestly, we may discover too late that what we preserved perfectly was the ritual — after losing the people.

It may be time to end the “Diaspora Day” before the Jews of the Diaspora slip further away.

Shammai Engelmayer is a rabbi-emeritus of Congregation Beth Israel of the Palisades and an adult education teacher in Bergen County. He is the author of eight books and the winner of 10 awards for his commentaries. His website is www.shammai.org.