WORD OF THE MONTH
A weekly feature of Torah Tidbits to help clarify practical and conceptual aspects of the Jewish Calendar, thereby better fulfilling the mitzva of HaChodesh HaZeh Lachem... 

This Shabbat we bench Rosh Chodesh Sivan, which falls on the following day, Sunday. Rosh Chodesh Sivan is always one day, since Iyar has only 29 days (in our fixed calendar).

ROSH CHODESH SIVAN YIHYEH MACHAR B'YOM RISHON HABA ALEINU V'AL KOL YISRA'EL L'TOVA:
The Molad of Sivan will be early Shabbat morning at 2:10am Isr. Summer Time.The traditional way to announce it is in Jerusalem Solar Time, as follows:
HAMOLAD HAYA HABOKER, SHLOSHIM V'ACHAT DAKOT V'CHELEK ECHAD ACHAREI ACHAT
In Rambam’s notation, the Molad is SHA 6 hrs. 559 parts
The astronomical (actual) molad is Shabbat morning, May 31, 7:21am

Calendar, Trivia, and Statistics
“These are a few of my favorite things” - Sound of Music
This Shabbat, we bench Rosh Chodesh Sivan, which is on Sunday - Machar Chodesh. Sunday is the first of Sivan. It is also the first of June. Since both Sivan and June have 30 days, the first of Tammuz will fall on the first of July. Tammuz has 29 days. July has 31. Put it all together and we have 59 days coming when the days of the month will be the same for the Jewish and secular calendars. The 30 days of Sivan and the 29 days of Tammuz. The first of Av will fall on the 30th of July, ending the 59-day match up.

A TT reader asked about the frequency of such an occurrence and if there could be more than 59 days in a row that match between the two calendars.
Let’s start with the match up of one month at a time. Any Jewish month can match up with a secular month for 29 or 30 days. Most months has one possible matching month from the other calendar. Tishrei, for example, can match up with October. (Over a thousand years ago, Tishrei could match September, but let’s leave that out of the discussion for now.) Chesh- van can match up with November, Kislev with December, Tevet with January, and Shvat with February. Adar (or the first of two Adars) can match up with February and March. Nissan and April, Iyar and May, Sivan and June, Tammuz and July, Av and August, Elul and September. From the time of a match up (or two in a row) until the next match up takes from 31 to 35 months (2½ to 3 years). Every so often a match up just misses, and the time between match ups roughly doubles, to more than 5 years between match ups.

As mentioned earlier, when two 30 months (one Jewish month, one secular month) match up, then the following months will also match. There are only four 30-day months in the secular calendar. Thirty days hath September, April, June, and November - remember that? So when Sivan and June match, then Tammuz and July will also. Most recently before this year, this double match up happened in 5744 (19 years ago). Before that, it happened in 5733 (11 years earlier) and 5725 (19 years before 5744). The next time it’s scheduled to happen is 5809 (which is two 19-year jumps and an additional 8 years).
Nissan-April (both 30 days) and Iyar- May also combine to the 59-day match up period. Most recent of those was 5755, and before that in 5736 (19 years ealier). The next one is scheduled for 5774 (19 years later) and then 46 years later in 5820.
[The range of years referred to here is too short to determine patterns.]

September-Elul is a matchup that cannot be followed by another match up, because Elul only has 29 days.
The final possibility for a double match up is Cheshvan-November followed by Kislev-December. This will work only when Cheshvan has 30 days (which it doesn’t always have). In 5739 there was a double match up, but in 5758, Cheshvan had 29 days, so Kislev- December didn’t match up. Next scheduled double is 5788. The Cheshvan-November and Kislev- December match up, though, gives us a period of 60 days of synchronous dates. that’s the most there can be.
Another interesting situation occurred in 5755 ('95) when Adar Alef matched February. They matched for 28 days and then March had a 2-day headstart on Adar Bet. Adar Bet has 29 days and March has 31, so Nissan and April matched up for their 30 days. This is followed by Iyar matching the first 29 days of May. That’s three months matched up within a 4-month period. That isn’t scheduled until 5850, 95 years later. (95 is five 19-year cycles.)
One more possibility. When Tevet matches up with January, Shvat starts two days before February. If February has 28 days, Shvat’s 30 days even things out so that Adar and March will match up. If February has 29 days, the second match up won’t happen. This double match up with a skipped month is scheduled for 5766.
It was mentioned earlier that more than a thousand years ago, Rosh HaShana fell on September 1st. That produced another double match up of Tishrei-September and Cheshvan- October. Over many centuries, there is small but noticeable shift in the calendar that adds other options.

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