The Lunar Eclipse Tetrads And The Jewish Calendar

The most spectacular thing I saw this week was the total lunar eclipse on Monday morning, which I observed from my parents' home in the New Forest - I could view it from the spare bedroom I was sleeping in.

There has been a lot of fuss made in certain circles about a tetrad and blood Moon and how these tie into Biblical prophecy. The Moon's orbit is inclined and some time back I wrote a post about the various lunar months. One of these is the draconic month of 27.21222 days, which is the time between successive crossings of the ascending node.

Basically, as the Moon's orbit is inclined, it will spend half its time above the ecliptic (the projection of the Sun's path onto the starry background) and half its time below. When it moves from below to above (as the northern hemisphere would reckon it), this is the ascending node. The synodic month - from New Moon to New Moon - is longer, and on average is 29.530589 days.

Now consider 6 synodic months - which is equal to 177.183534 days. This is 6.511 draconic months. So, if the Moon was crossing the ascending node at Full Moon, then 6 Full Moons later it would be near the descending node.

So, what can happen if conditions are right are that there is a lunar eclipse, and then lunar eclipses 6, 12 and 18 synodic months later. If these are all total eclipses, then we have what is now termed the tetrad.

And this week's was the fourth in a tetrad.

What has caused some excitement is that this fell on the Jewish festival of Sukkot, and all the total lunar eclipses in this tetrad were on Sukkot or Pesach.

Now, if you look at the Jewish calendar, then you will see that most years have 12 months - which are lunar months. So, a Full Moon will fall mid-month, every month. And the other obvious thing is that there is 6 months from Nissan (the month which Pesach falls in) to Tishri (the month that Sukkot falls in). And often there is 6 months from Tishri to Nissan.

In a tetrad, the eclipses will be 6 Jewish months apart.

So, if the first lunar eclipse of a tetrad is in the month of Nissan, then we will have the pattern:

Nissan-Tishri-Nissan-Tishri

if the first eclipse doesn't fall in a leap year. If it does, then the pattern becomes:

Nissan-Tishri-Adar Beit-Elul

Another pattern involving a leap year is possible, when the first lunar eclipse of a tetrad is in the month of Iyyar, which is the month that follows Nissan:

Iyyar-Cheshvan-Nissan-Tishri

If the first lunar eclipse of a tetrad is in the month of Tishri, then we will have the pattern:

Tishri-Nissan-Tishri-Nissan

if there are no leap years involved. If there are, then the pattern becomes:

Tishri-Nissan-Tishri-Adar Beit

or

Tishri-Adar Beit-Elul-Adar

depending on where the leap year is.

Hence, it is possible in a tetrad for two total lunar eclipses to be in Nissan (and hence fall on Pesach) and the other two to be in Tishri (and hence fall on Sukkot).

One factor in the excitement around this tetrad is that, apparently, whenever there is a tetrad where all the eclipses occur at Pesach and Sukkot, then there are significant events that happen relating to the Jewish people and/or the state of Israel - although as one list shows, these can be very tenuous (interestingly, that website declares there was no tetrad around the Crucifixion of Jesus, which not every tetrad fan agrees with - and there is a good article on the Answers In Genesis website which demonstrates that references to a blood-red moon at the Crucifixion were not a lunar eclipse).

As with Comet 1P/Halley, when you allow yourself to go a few years either side of an astronomical event, you can always find something important happening.

We can use NASA's lunar eclipse page (which has a list from 2000 BC to AD 3000)* to see where tetrads will be in the future, and a Hebrew calendar converter to see which month these fall into.

[* This also gives the number of tetrads in each century - interestingly it states there were no tetrads in the first century, listing the Pesach AD 33 eclipse as a partial - the one the previous Pesach is listed as total, but not visible from Jerusalem]

In the lists below, dates in bold are when the whole eclipse is visible from Jerusalem, and those in bold italics are where some of the eclipse is visible from Jerusalem.

Begin by looking at the rest of the twenty-first century:

2032/2033

Date	Jewish month and year
25 April 2032	Iyyar 5792
18 October 2032	Cheshvan 5793
14 April 2033	Nissan 5793
8 October 2033	Tishri 5794

2043/2044

Date	Jewish month and year
25 March 2043	Adar Beit 5803
19 September 2043	Elul 5803
13 March 2044	Adar 5804
7 September 2044	Elul 5804

2050/2051

Date	Jewish month and year
6 May 2050	Iyyar 5810
30 October 2050	Cheshvan 5811
26 April 2051	Iyyar 5811
19 October 2051	Cheshvan 5812

2061/2062

Date	Jewish month and year
4 April 2061	Nissan 5821
29 September 2061	Tishri 5822
25 March 2062	Adar Beit 5822
18 September 2062	Elul 5822

2072/2073

Date	Jewish month and year
4 March 2072	Adar 5832
28 August 2072	Elul 5832
22 February 2073	Adar Rishon 5833
17 August 2073	Av 5833

2090/2091

Date	Jewish month and year
15 March 2090	Adar Beit 5850
8 September 2090	Elul 5850
5 March 2091	Adar 5851
29 August 2091	Elul 5851

When we move on to the twenty-second century, there are 4 tetrads:

2101/2102

Date	Jewish month and year
14 February 2101	Shevat 5861
9 August 2101	Av 5861
3 February 2102	Shevat 5862
30 July 2102	Av 5862

2119/2120

Date	Jewish month and year
25 February 2119	Adar Rishon 5879
20 August 2119	Av 5879
14 February 2120	Shevat 5880
9 August 2120	Av 5880

2137/2138

Date	Jewish month and year
7 March 2137	Adar 5897
30 August 2137	Elul 5897
24 February 2138	Adar Rishon 5898
20 August 2138	Av 5898

2155/2156

Date	Jewish month and year
19 March 2155	Adar Beit 5915
11 September 2155	Elul 5915
7 March 2156	Adar 5916
30 August 2156	Elul 5916

That is the last tetrad for nearly 300 years - there are none in the twenty-third or twenty-fourth centuries, but when we come to the twenty-fifth century, there are 4 tetrads:

2448/2449

Date	Jewish month and year
17 June 2448	Sivan 6208
10 December 2448	Kislev 6209
6 June 2449	Sivan 6209
30 November 2449	Kislev 6210

2466/2467

Date	Jewish month and year
28 June 2466	Tammuz 6226
22 December 2466	Tevet 6227
18 June 2467	Sivan 6227
11 December 2467	Kislev 6228

2477/2478

Date	Jewish month and year
28 May 2477	Sivan 6237
21 November 2477	Kislev 6238
17 May 2478	Iyyar 6238
10 November 2478	Cheshvan 6239

2495/2496

Date	Jewish month and year
8 June 2495	Sivan 6255
2 December 2495	Kislev 6256
27 May 2496	Sivan 6256
21 November 2496	Kislev 6257

When we come to the twenty-sixth century, things pick up, with there being 7 tetrads totally within this century:

2506/2507

Date	Jewish month and year
8 May 2506	Iyyar 6266
2 November 2506	Cheshvan 6267
28 April 2507	Iyyar 6267
22 October 2507	Cheshvan 6268

2524/2525

Date	Jewish month and year
19 May 2524	Iyyar 6284
12 November 2524	Cheshvan 6285
8 May 2525	Iyyar 6285
1 November 2525	Cheshvan 6286

2542/2543

Date	Jewish month and year
30 May 2542	Sivan 6302
23 November 2542	Kislev 6303
20 May 2543	Iyyar 6303
12 November 2543	Cheshvan 6304

2564/2565

Date	Jewish month and year
29 March 2564	Nissan 6324
21 September 2564	Tishri 6325
18 March 2565	Adar Beit 6325
11 September 2565	Elul 6235

2571/2572

Date	Jewish month and year
11 May 2571	Iyyar 6331
3 November 2571	Cheshvan 6332
29 April 2572	Iyyar 6332
22 October 2572	Cheshvan 6333

2582/2583

Date	Jewish month and year
9 April 2582	Nissan 6342
3 October 2582	Tishri 6343
29 March 2583	Nissan 6343
22 September 2583	Tishri 6344

2589/2590

Date	Jewish month and year
21 May 2589	Iyyar 6349
13 November 2589	Cheshvan 6350
10 May 2590	Iyyar 6350
2 November 2590	Cheshvan 6351

Then there is a century-straddling tetrad:

2600/2601

Date	Jewish month and year
20 April 2600	Nissan 6360
14 October 2600	Tishri 6361
9 April 2601	Nissan 6361
4 October 2601	Tishri 6362

Like its predecessor, the twenty-seventh century contains 7 complete tetrads:

2611/2612

Date	Jewish month and year
20 March 2611	Adar Beit 6371
14 September 2611	Elul 6371
9 March 2612	Adar 6372
2 September 2612	Elul 6372

2618/2619

Date	Jewish month and year
1 May 2618	Iyyar 6378
25 October 2618	Cheshvan 6379
20 April 2619	Nissan 6379
15 October 2619	Tishri 6380

2629/2630

Date	Jewish month and year
31 March 2629	Nissan 6389
24 September 2629	Tishri 6390
26 March 2630	Adar Beit 6390
13 September 2630	Elul 6390

2640/2641

Date	Jewish month and year
29 February 2640	Adar 6400
23 August 2640	Elul 6400
17 February 2641	Adar Rishon 6401
13 August 2641	Av 6401

2647/2648

Date	Jewish month and year
11 April 2647	Nissan 6407
5 October 2647	Tishri 6408
31 March 2648	Nissan 6408
23 September 2648	Tishri 6409

2658/2659

Date	Jewish month and year
11 March 2658	Adar 6418
4 September 2658	Elul 6418
1 March 2659	Adar 6419
24 August 2659	Elul 6419

2676/2677

Date	Jewish month and year
22 March 2676	Adar Beit 6436
14 September 2676	Elul 6436
11 March 2677	Adar 6437
3 September 2677	Elul 6437

After this, there is another lengthy gap, with no tetrads in either the twenty-eighth or twenty-ninth centuries, while the thirtieth century has just one:

2987/2988

Date	Jewish month and year
2 July 2987	Tammuz 6747
26 December 2987	Tevet 6748
21 June 2988	Sivan 6748
14 December 2988	Kislev 6749

So, these are the tetrads for the remainder of the third millennium. We can now look at which tetrads include eclipses occurring on Pesach or Sukkot:

Tetrad	Number of total eclipses on:
	Pesach	Sukkot
2032/2033	1	1
2061/2062	1	1
2564/2565	1	1
2582/2583	2	2
2600/2601	2	2
2618/2619	1	1
2629/2630	1	1
2647/2648	2	2

This means that in the third millennium there are 3 more occassions where there is a tetrad comprised of 2 total lunar eclipses on Pesach and 2 on Sukkot.