How the calendar might look with a Sanhedrin

It is an interesting exercise to attempt to compare what the Sanhedrin might announce to the calculated calendar that we use

While the molad is announced in terms of Jerusalem Solar Time, the tables below are shown in terms of Israeli clock time, based of the time zone (UTC +2). This allows the announced molad to be compared to the actual astronomical conjunction. The announced molad is based on the average calculated lunar cycle.

For the actual conjunction, sunset, and moonset times, I used the time charts at Time and Date along with a guess at visibility based on .6 of the time between sunset and moonset.
I assumed the Sanhedrin magically came into existence in time to declare Cheshvan because I did not want to deal with Rosh Hashannah of this year.

I also took the calculated Molad (Solar Time in Yerushalayim) and converted it to the Israeli Time Zone (UTC + 2) Clock Time as explained by Torah Tidbits in Yerushalayim. For example, the 5770 table gives the time as the Rambam declares it, as we currently announce it, and accordint to Israeli Clock Time. Thus, the time being shown is clock time rather than the actual announced time. This difference is based on the fact that noon in Solar Time (as used in the announced molad) is approximately 11:40 AM by the clock.

The point is to show what the effects would be with the various possibilities as the year progresses. I left out Rosh Hashanna because it seems that when you get a "two day" situation, Rosh Hashanna becomes Tishrei 1 and 2 rather than Elul 30 and Tishrei 1. The reason being that the entire idea of two days is based on the waiting for the declaration and the way korbanos are handled. Since Rosh Hashanna starts as soon as the declaration is made and everywhere in the country treats it as two days mishum safek, it is possible that the way we handle the same situation with every other month would be different. In any case, the entire set of comments was to show how the differences would propagate through the year.

Calculated Molad chart for the year 5770

Month	Date	Israel Time	Rosh Chodesh
Cheshvan	Sunday, October 18, 2009	11:10 PM IST	Sun/Mon Oct 18/19
Kislev	Tuesday, November 17, 2009	11:54 AM IST	Tue/Wed Nov 17/18
Teves	Thursday, December 17, 2009	12:39 AM IST	Fri, Dec 18
Shvat	Friday, January 15, 2010	1:23 PM IST	Sha Jan 16
Adar	Sunday, February 14, 2010	2:07 PM IST	Sun/Mon Feb 14/15
Nisan	Monday, March 15, 2010	2:51 PM IST	Tue, Mar 16
Iyar	Wednesday, April 14, 2010	4:35 AM IDT	Wed/Thu Apr 14/15
Sivan	Thursday, May 13, 2010	5:19 PM IDT	Fri May 14, 2010
Tamuz	Saturday, June 12, 2010	6:03 AM IDT	Sha/Sun Jun 12/13
Av	Sunday, July 11, 2010	6:47 PM IDT	Mon, Jul 12
Elul	Tuesday, August 10, 2010	7:31 AM IDT	Tue/Wed Aug 10/11

This table shows the actual (astronomical) time of the new moon (conjunction) in Israel Time. This can be gotten from a number of tables, such as the Naval Observatory time showed in the previous posting.

Astronomical Conjunction chart for 5770

Month	Date	Israel Time
Cheshvan	Sunday, October 18, 2009	7:33 AM IST
Kislev	Monday, November 16, 2009	9:14 PM IST
Teves	Wed, December 16, 2009	12:39 AM IST
Shvat	Friday, January 15, 2010	1:23 PM IST
Adar	Sunday, February 14, 2010	2:07 PM IST
Nisan	Monday, March 15, 2010	2:51 PM IST
Iyar	Wednesday, April 14, 2010	4:35 AM IDT
Sivan	Friday, May 14, 2010	5:19 PM IDT
Tamuz	Saturday, June 12, 2010	6:03 AM IDT
Av	Sunday, July 11, 2010	6:47 PM IDT
Elul	Tuesday, August 10, 2010	7:31 AM IDT

Calculated Average Molad chart for the year 5771

Month	Day	Molad	Israel Clock Time	Rosh Chodesh
Cheshvan	30 Tishri 5771 Fri 8 Oct 2010	08:20:02 AM	7:59 AM IST	Fri/Sha Oct 8/9
Kislev	30 Cheshvan 5771 Sat 6 Nov 2010	09:04:03 PM	8:43 PM IST	Sun/Mon Nov 7/8
Teves	29 Kislev 5771 Mon 6 Dec 2010	09:48:04 AM	9:27 AM IST	Tue/Wed Dec 7/8
Shvat	29 Teves 5771 Tue 4 Jan 2011	10:32:05 PM	10:11 PM IST	Thu Jan 6
Adar I	29 Shevat 5771 Thu Feb 3 2011	11:16:06 AM	10:55 AM IST	Fri/Sha Feb 4/5
Adar II	28 Adar A 5771 Fri March 4 2011	12:00:07 AM	11:39 PM IST	Sun/Mon Mar 6/7
Nisan	28 Adar B 5771 Sun April 3 2011	12:44:08 PM	1:23 AM IDT	Tue Apr 5
Iyar	29 Nisan 5771 Mon May 3 2011	01:28:09 AM	2:08 AM IDT	Wed/Thu May 4/5
Sivan	28 Iyar 5771 Wed June 1 2011	02:12:10 PM	2:52 PM IDT	Fri June 3
Tamuz	29 Sivan 5771 Fri July 1 2011	02:56:11 AM	3:36 AM IDT	Sha/Sun July 2/3
Av	28 Tamuz 5771 Sat July 30 2011	03:40:12 PM	4:20 PM IDT	Mon Aug 1
Elul	29 Av 5771 Mon Aug 29 2011	04:24:13 AM	5:04 AM IDT	Tue/Wed Aug 30/31

Dr. Roy Hoffman of the Israel new Moon Society has said that  

The best time to see the crescent Moon, according to my research ("Observing the new Moon" R. E. Hoffman, Monthly Notes Roy. Astron. Soc., 340, 1039-1051 (2003).), is 0.6 of the time between Sunset and Moonset. The first crescent Moon appears between 15 and 55 hours after the true conjunction.

He has published predictions of possible first sightings of the new moon at

You can download my predictions for the next year at http://chem.ch.huji.ac.il/nmr/foo/handouts/5771e.pdf, and for last year at http://chem.ch.huji.ac.il/nmr/foo/handouts/5770e.pdf

Some of these estimates show that the moon would definitely not be visible to the naked eye at that time.

I should point that that as Dr. Hoffman says

 I do not publish calendars based on sightings because we are commanded to use our calculated calendar until a recognized Sanhedrin rules otherwise. If you do publish such a calendar, it is more than likely that a few individuals will follow it in contradiction to the halakhah.

Rosh Hashanna of 5772 will be Thu/Fri Sept 29/30

The actual conjunction and the possible “first visibility” list is shown below.

Note that the first visibility range is delayed because the first date is October 8, 5:16 PM – 5:26 PM. This is probably too short a time to actually see the moon. The following month, the first moonrise is at 4:45 PM which is less than ten hours. If the moon is seen on or before day 29 of the month, then the Sanhedrin would be able to declare the next day Rosh Chodesh and the previous month would be a 29 day month. Otherwise, the previous day would be a two day Rosh Chodesh by default. This occurs for Chesvan and Kislev. Note that Teves has two possibilities. If witnesses see the moon at the first available date (Dec 6), then Dec 7 would be the only day of Rosh Chodesh, unlike the calculated calendar which has two days. This would make the fast of Asara B'Teves occur one day earlier, Thursday, December 16, instead of Friday, December 17. This would also affect the declaration of the month of Shvat. Since it is the middle of the rainy season, it is very probable that the witnesses would miss the first sighting of the moon, forcing Teves to have tw days of Rosh Chodesh, just like the calculated calendar.

If Teves only had one day of Rosh Chodesh (December 7), then January 5 would be day number 30 of that month. This would force Shvat to have a two day Rosh Chodesh and would bring it back in sync with the calculated calendar.

Adar II now has two possibilities again because of the end of the rainy season. It is also possible that it would be missed because of the early time within the rang that the visibility occurs (19 hours 18 minutes). If it were visible, the Sanhedrin might deliberately not hold court because it would force Purim to occur on Shabbos. This affects Nisan, just as Teves did Shvat.

Note that Daylight Savings Time in Israel starts April 2. Thus, All time from April on are in Daylight Savings Time.

Nisan now has three possibilities because of the tw possibilities of Adar II. If Adar II had only one day Rosh Chodesh, then Nisan is forced to have two days Rosh Chodesh and comes back into sync with the calculated calendar. This is the same situation as if Adar II had two days Rosh Chodesh and the witnesses saw the moon in time for Nisan to have one day Rosh Chodesh. It is probable that they would see it as the moon would be 26 hours old. If they do not see it, Nisan has two days Rosh Chodesh and Pesach becomes Wednesday April 20 instead of Tuesday April 19. This is a significant effect and shows why we need the calendar to be precise. This also shows the reason for two days of Yom Tov in Chutz La'Aretz.

Iyar can now be either a one day or two day Rosh Chodesh depending on what had happened with Nisan (assuming that the witnesses do see the moon at the designated time. If they miss the moon, it would of course be forced to be a two day Rosh Chodesh.

Because Shavuos is defined as being counted from Pesach, the date would have been defined by what happened to Nisan.

Had Iyar had a single day of Rosh Chodesh, June 2 would have been the thirtieth day of the month forcing two days of Rosh Chodesh whether the moon was seen or not. If there had been two days of Rosh Chodesh, it would have again depended on whether or not the moon had been seen. This would set up three possibilities.

This sets up three possibilities for Sivan, but the first of Sivan woul occur on either June 3 or 4. This leads to Tamuz having one or two days Rosh Chodesh, but in either case, the first of the month is July 3. This brings it back in sync with the calculated calendar.

Av can now have one or two days Rosh Chodesh, meaning that Tisha B'Av can be on August 9 or 10.

While the moon on the day of the conjunction of Elul (Aug 29) may be visible, the time interval is only two minutes so it would probably be too close to the sun. If we assume that the second interval is seen, then the first of Elul is on the same day in either case. This allows Rosh Hashana to start as expected by the calculated calendar. On the other hand, if that day is not seen, Elul starts even later and causes a problem with Rosh Hashana because Elul 29 is pushed forward to September 29.

The Conjunction for Rosh Hashana 5772 is September 27 at 2:09 Am, with a possible visibility at 6:45 PM on September 28 (40 h 36 m moon age). This is Elul 29 according to the analysis above, which would make Rosh Hashanna occur on September 29 and 30. This is the same as determined by the calculated calendar.

Conjunction chart for the year 5771

Month	Conjunction	Visibility Range	“best Time” (.6 of way)	Rosh Chodesh
Cheshvan	Thu, Oct 7, 2010 8:44 PM IST	Oct 9 5:14 – 6:10 PM	5:47 PM 45 h 3 m	Fri/Sha Oct 8/9
Kislev	Sat, Nov 6, 2010 6:52 AM IST	Nov 7 4:45 – 5:36 PM	5:15 PM 34 h 23 m	Sun/Mon Nov 7/8
Teves	Sun, Dec 5, 2010 7:36 PM IST	Dec 6 4:35 – 5:14 PM	4:58 PM 21 h 22 m	Tue Dec 7
Teves	Sun, Dec 5, 2010 7:36 PM IST	Dec 7 4:35 – 6:16 PM	5:35 PM 46 h 50 m	Tue/Wed Dec 7/8
Shvat	Tue, Jan 4, 2011 11:03 AM IST	Jan 4 4:48 – 5:00 PM	4:55 PM 5 h 52 m	Too early to see
Shvat	Tue, Jan 4, 2011 11:03 AM IST	Jan 5 4:49 – 5:59 PM	5:31 PM 30 h 28 m	Wed/Thu Jan 5/6
Shvat	Tue, Jan 4, 2011 11:03 AM IST	Jan 5 4:49 – 5:59 PM	5:31 PM 30 h 28 m	Thu Jan 6
Adar I	Thu, Feb 3, 2011 4:31 AM IST	Feb 3 5:15 – 5:45 PM	5:33 PM 13 h 2 m	Too early to see
Adar I	Thu, Feb 3, 2011 4:31 AM IST	Feb 4 5:16 – 6:39 PM	6:15 PM 13 h 44 m	Fri/Sha Feb 4/5
Adar II	Fri, Mar 4, 2011 10:46 PM IST	Mar 5 5:40 – 6:20 PM	6:04 19 h 18 m	Sun Mar 6
Adar II	Fri, Mar 4, 2011 10:46 PM IST	Mar 6 5:40 – 7:13	6:35 PM 43 h 49 m	Sun/Mon Mar 6/7
Nisan	Sun, Apr 3, 2011 5:32 PM IDT	April 4 7:00 – 7:57 PM	7:34 PM 26 h 2 m	Mon/Tue Apr 4/5
Nisan	Sun, Apr 3, 2011 5:32 PM IDT	April 4 7:00 – 7:57 PM	7:34 PM 26 h 2 m	Tue Apr 5
Nisan	Sun, Apr 3, 2011 5:32 PM IDT	April 5 7:01 – 8:52 PM	7:37 PM 50 hours 5 m	Tue/Wed Apr 5/6
Iyar	Tue, May 3, 2011 9:51 AM IDT	May 3 7:20 – 7:42 PM	7:33 PM 9 h 42 m	Too early to see
Iyar	Tue, May 3, 2011 9:51 AM IDT	May 4 7:21 – 8:39	8:07 PM 34 h 16 m	Wed/Thu May 4/5
Iyar	Tue, May 3, 2011 9:51 AM IDT	May 4 7:21 – 8:39	8:07 PM 34 h 16 m	Wed May 4
Sivan	Thu, Jun 2, 2011 12:03 AM IDT	Jun 2 7:40 – 8:21 PM	8:04 PM 20 h 1 m	Thu/Fri June 2/3
Sivan	Thu, Jun 2, 2011 12:03 AM IDT	Jun 2 7:40 – 8:21 PM	8:04 PM 20 h 1 m	Fri June 3
Sivan	Thu, Jun 2, 2011 12:03 AM IDT	Jun 3 7:40 – 9:12 PM	8:35 PM 44 h 32 m	Fri/Sha June 3/4
Tamuz	Fri, Jul 1, 2011 11:54 AM IDT	July 2 7:49 – 8:39	8:19 PM 32 h 25 m	Sha/Sun July 2/3
Tamuz	Fri, Jul 1, 2011 11:54 AM IDT	July 2 7:49 – 8:39	8:19 PM 32 h 25 m	Sun July 3
Av	Sat, Jul 30, 2011 9:40 PM IDT	July 31 7:37 – 7:55 PM	7:47 PM 22h 7 m	Mon Aug 1
Av	Sat, Jul 30, 2011 9:40 PM IDT	Aug 1 7:36 – 8:32 PM	8:09 PM 46 h 29 m	Mon/Tue Aug 1/2
Elul	Mon, Aug 29, 2011 6:04 AM	Aug 30 7:06 – 7:42	7:27 PM 37 h 23 m	Tue/Wed Aug 30/31
Elul	Mon, Aug 29, 2011 6:04 AM	Aug 30 7:06 – 7:42	7:27 PM 37 h 23 m	Wed Aug 31

How a Sanhedrin might not change the printed calendar this year

 The time and date calendar can be used to estimate if the eidim can see the moon after the astronomical molad and allow us to guess if the Sanhedrin would declare the new month on the same or a different day than calculated by our fixed calendar.

For example, the astronomical molad for Cheshvan is 8:44 PM October 7. The moon times for October 8 are 6:12 AM rising and 5:26 PM setting. The noon % illumination is .8% at 11:52. The sunrise and sunset times are 5:37 and 5:16. Thus, it would probably not be visible at moonrise.  The noon illumination on October 9 is 4.1 % at 12:49.  I would therefore guess that the visibility during this time would be about 1%. This may be visible during the ten minutes after sunset and before moonset (about 17 hours after the astronomical molad). This would mean that Beis Din could not declare the chodesh until October 9 (since they must do so during the day). This would mean that the declared month would match the calculated month and Tishrei would have 30 days as the printed calendars show.

Kislev has the astronomical new moon at 6:52 AM on November 6, which seems to imply that eidus between moonset and sunset on November 6 might be possible however moonset and sunset are both 4:45 PM so it would probably be drowned out.  If it was visible, Cheshavan would be a 29 day month, while if not (as is most probable) it would be a 30 day month as shown in the printed calendar

This seems to show that for at least Cheshvan and Kislev, the Sanhedrin would most probably declare the chodesh to be the same as our calculated calendar.  It might be interesting to estimate what might happen during the rest of the months of the year and see what would have to be done to ensure that next Rosh Hashannah did not come out on one of the "forbidden" dates.

There are sites that calculate the percent visibility of the moon for a specific date and time. For example, the U.S. Naval observatory says

Although the date and time of each New Moon can be computed exactly (see, for example, Phases of the Moon in Data Services), the visibility of the lunar crescent as a function of the Moon's "age" - the time counted from New Moon - depends upon many factors and cannot be predicted with certainty. In the first two days after New Moon, the young crescent Moon appears very low in the western sky after sunset, and must be viewed through bright twilight. It sets shortly after sunset. The sighting of the lunar crescent within one day of New Moon is usually difficult. The crescent at this time is quite thin, has a low surface brightness, and can easily be lost in the twilight. Generally, the lunar crescent will become visible to suitably-located, experienced observers with good sky conditions about one day after New Moon. However, the time that the crescent actually becomes visible varies quite a bit from one month to another. The record for an early sighting of a lunar crescent, with a telescope, is 12.1 hours after New Moon; for naked-eye sightings, the record is 15.5 hours from New Moon. These are exceptional observations and crescent sightings this early in the lunar month should not be expected as the norm.
Obviously, the visibility of the young lunar crescent depends on sky conditions and the location, experience, and preparation of the observer. Generally, low latitude and high altitude observers who know exactly where and when to look will be favored. For observers at mid-northern latitudes, months near the spring equinox are also favored, because the ecliptic makes a relatively steep angle to the western horizon at sunset during these months (tending to make the Moon's altitude greater).

I would guess that they must have had some occurrance that managed to make it within 15.5 hours (in perfect conditions) in order to set the record. I saw that they did not say when the record was set. Phil Chernofsky has told me that the Israel New Moon Society uses a figure of 18 - 20 hours after the conjuction (astronomical molad) for the earliest possible visibility. I think that if we use the 18 hour figure to get the % of illumination we could calculate. Given that 29.5 days is 708 hours, 18 - 20 hours is approximately 5% - 6% illuminated. We can then use the illumination table to estimate if the moon would be seen around moonset on a particular day. This assumes that the eidim would see the moon between sunset and moonset only. Thus, I would add 18 hours to the conjunction and go to the next sunset time for that estimate.

The Naval observatory calculator generates a table for the year showing the percent illuminated for each day at midnight or noon in Universal Time or one of the U.S. timezones. This would be 7 hours earlier than the time shown for Yerushalayim. The South African Astronomical Observatory has a table of predictions showing where the moon would be visible as well as when it is first visible in South Africa. Another calculator is found at the fishing site http://www.noreast.com/moon/ This calculates the % illuminates at a set hour for a given day. It appears that this is also Eastern Time. Because the Muslims still use "eidus" as the start of their months, they have developed algorithms and maps showing where the moon would be visible.

A set of predictions and maps can be seen at HM Nautical Almanac Office This shows the best time to see the previous new moon for the location requested at the standard time for the first three days of the new moon. It also gives an estimate of the ease of the sighting. For example, September 8 shows the best tim at 5:48 PM with a classification of F. September 9 is 6:04 PM with a classification of C, September 10 is 6:20 PM with a classification of A. The following month is shown with a set of three maps showing the area of the world which can see the moon, but it is more difficult to read. There is no data other than those two months.

There is a Java Applet which gives the location, moon age,  and illumination for specific times at specific locations. Yerushalayim is not listed but the latitude (32.083333 N) and longitude (34.8 E) can be entered explicitly. Use the time about halfway (4/9) between sunset and moonset for the estimate being used.


Month          Best time      Pct      Age

Cheshvan     Oct 8, 1721   1.7%   1d 02h 33m  
Kislev          Nov 7, 1651   3.5%   1d 15h 55m





Cheshvan

Why four out of five years (5771 - 5775) start on Thursday - Friday

The Jewish year has three possibilities for the number of days in a regular or leap year. The reason is that the lunar month is approximately 29.5 (twenty nine and a half) days long. If this was exact, then just alternating 29 and 30 day months would be correct. However, the exact average cycle is 29 days 12 hours 793 "parts" in length. A "part" is one in 1080 of an hour. The 793 "parts" converts to 44 minutes and 1 "part" as can be seen by looking at a chart of the molad announcements for the year. As a result, there are almost 15 minutes more than 29.5 days. This is handled by having the months of Cheshvan and Kislev be either 29 or 30 days and having the three possibilities of 29 and 29, 29 and 30, or 30 and 30. This calculation actually differs from the astronomical new moon as the year progresses. It is calculated by the total number of days in a lunar year and dividing by twelve. As a result, the actual molad can vary from the calculated value by as much as 10 hours.

Rosh Hashannah (first day) can never occur on Sunday, Wednesday, or Friday so that Yom Kippur cannot occur on Friday or Sunday and Hoshannah Rabbah can never occur on Shabbos.

Judaism 101 gives an interesting mnemonic for determining the leap years in the cycle using a piano keyboard

As can be seen the leap years are years 3, 6, 8, 11, 14, 17, and 19 (0).

This means that the pattern for these 5 years are L R R L R

A more detailed explanation is here

This makes the regular year have 353, 354, and 355 days ("adding 3, 4, or 5 days to the day of the week of Rosh Hashannah), while leap years have 383, 384, and 385 days ("adding" 5, 6, and 0). The Jewish year uses a 19 year cycle and the leap years can be shown by taking the year number as modulus 19. This year (5771) is year 14 of the cycle (year 19 of the cycle has modulus 0). The five years involved are thus 14, 15, 16, 17, 18 Year "17" is the next leap year. This year (a leap year) both Cheshvan and Kislev are 30 days so that next Rosh Hashannah (5772) will be also be on Thursday and Friday. The following year will have Cheshvan 29 days and Kislev 30 days (30 Kislev 5772 is 26 December 2011). This brings the following Rosh Hashannah (5773) to Monday and Tuesday. .

5773 will have 29 days in Cheshvan and Kislev which brings Rosh Hashannah back to Thursday again (from the modulus calculation above.) for 5774.

5774 is year 17 of the 19 year cycle and is again a leap year and again will have both Cheshvan and Kislev set to 30 days. This means that the following (regular) year of 5775 will again start on Thursday.

Since 5775 is not a leap year, Rosh Hashannah of 5776 will occur on Monday and since it is again a leap year (modulus number 0) with both Cheshvan and Kislev 30 days, the following year (5777) is again on Monday.

Larry Nussbaum pointed out by email the following five years starting with 5776 are L R R L R as well with the leap year again being "full" (both Cheshvan and Kislev having 30 days) This means that four out of those five years start on Monday, with the "off year" being Thursday. The last year of this pattern (5780) is year number 4 of the cycle, so 5781 (year 5), which starts on Shabbos,  is also regular and 5782 starts on Tuesday. 

This double pattern is quite rare. This appears to be to only such pattern (2 sets of 4 out of 5 back to back) in the past 247 years. In 5760 - 5764 we had 4  of 5 years with RH on Shabbos. There is no short cycle (like 19 or 28 years) when it comes to days of the week for yom tovim. The only cycle is a 247 year cycle (and that's not 100% guaranteed). Mr. Nussbaum also pointed out that the Tur has a 247 year calendar.

I saw this on the Mail Jewish mailing list, from Richard Fiedler

Mail.Jewish Mailing List
Volume 59 Number 26
Produced: Tue, 14 Sep 2010 01:15:16 EDT
From: Richard Fiedler
Date: Mon, Sep 13,2010 at 10:01 PM
Subject: Dates of Rosh HaShanah

Rosh HaShanah 2013 has another extremely unusual aspect. The Old Moon will be visible on Wednesday Morning Sept 4, 2013 and we will welcome in Rosh HaShanah Wednesday Night.

The Molad of Tishrei 2013 will be Yom Chamishi (Thursday), 16 hours 830 parts. This is under the window of the Molad Zaqen rule (18 hours causes a deferral of Rosh HaShanah) that normally prevents as Old Moon from being seen Erev Rosh HaShanah.

If you will join me in Jerusalem that week I will be on Mount Scopus at 5:10 AM when the Moon will rise. The Sun will rise at 6:16 AM. We will be seeing the cause of the Gemora of Rabban Gamliel and Rabbi Yehoshua (120 CE).

The reason for this is rooted in a very exceptional lunar orbit which is taking a path below the African Continent. Here is a link to the R H van Gent chart of Lunar Visibility for that date. https://files.me.com/richardfiedler/tfsa4d

The above comment shows the "old moon" being visible the day before Rosh Hashanah by the fixed calendar. I realized as a result of a comment that I received that the Sanhedrin is based on eidus, which means that the eidim had to have seen the new moon. IIRC this is a minimum of six hours after the actual astronomic molad, which oscillates around the average announced molad. Actually, a member of the Israel New Moon Society has told me that the new moon would not be visible to the naked eye until it is at least 18 -20 hours old. The question would be when the actual astronomic "new moon" would be. I looked up on the internet and  went to a planetary body calendar website to get these values. Note that the current rule is that Daylight time in Israel ends the Sunday morning before Yom Kippur. As a result, DST ends September 8. The times shown below are therefore in Daylight Savings Time.

Moonrise and moonset in Jerusalem (DST)

Date	Moonrise	Moonset

Sep 4, 2013   5:10 AM       6:09 PM

Sep 5, 2013   6:06 AM       6:43 PM

Meridian Passing

                     Sep 4                    Sep 5      
Time:           11:42 A.M.          12:27 P.M.
Altitude:       65.6°                    61.4°
Distance:     396,157 km          392,621 km.
Illuminated: 1.5%                    0.1%

Phase: New at 2:37 P.M. Sep 5

I also checked and sunrise is 6:16 and 6:17 A.M. and sunset is 6:59 P.M. and 6:58 PM on those days. This seems to imply that IF the six hour time is correct, then the new moon would probably not be visible until 8:43 P.M. which is well after moonset. Note that the .1% illumination is at the meridian (which is "drowned out" by the noon sun) If the two hours before the new moon are linear to the 4 hours after the new moon, then the illumination would be no more than .2% and the six hours would be about .3% The previous days meridian shows 4.8% illumination which would make the moonrise illumination about 2.5%, with the sun still below the horizon. This may indeed allow it to be seen. In the case of the new moon, since the moon sets 15 minutes earlier than the sun, it would seem to be very difficult to see it. The illumination at the meridian for the day after the new moon (approximately 22 hours) is 1.0%.  If the 18 hour estimate mentioned earlier is correct, this implies that the old moon would indeed have been visible.

When the Sanhedrin is reestablished, there will be a set of 30 day months until Rosh Chodesh gets co-ordinated with the eidus and astronomical molad rather than the fixed average molad that we announce now. As a result the Sanhedrin would have had to be established a number of months before this so that Rosh Hashannah could be on Shabbos (September 7) while Elul remained 29 days.