The order of months that are Malei/Chaseir and the months of Cheshvan/Kisleiv

* This article is an excerpt from the above Sefer

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The order of months that are Malei/Chaseir and the months of Cheshvan/Kisleiv:[1]

The month of Teves is always Chaseir and from it begins the cycle of one-month Malei and one month Chaseir until the month of Cheshvan. Starting from the month of Cheshvan this cycle ends, depending on the year. In some years both Cheshvan and Kisleiv are Malei, thus having three consecutive Malei months [Tishrei, Cheshvan, and Kisleiv]. This type of year is called a Shleima/complete year. In this year the lunar year contains 355 days. In other years both Cheshvan and Kisleiv are Chaseir, thus having three consecutive Chaseir months [Cheshvan, Kisleiv, and Teves]. This type of year is called a Chaseira/incomplete year. In this year the lunar year contains 353 days. In other years Cheshvan is Chaseir and Kisleiv is Malei, thus following regular pattern of Chaseir/Malei throughout all 12 months of the year. This type of year is called a Kesidran [proper order] year. In this year the lunar year contains 354 days. In no year is Cheshvan Malei and Kisleiv Chaseir. In total there are ten predetermined fixed months of Chaseir/Malei, five months being always Malei and five months being always Chaseir, with two months remaining interchangeable. [Look at Table]

A leap year:[2] In a leap year the first Adar is always Malei while the second Adar is always Chaseir. This breaks the cycle of Chaseir/Malei that was started in Teves, as we now have two consecutive months of Malei [Shevat and Adar 1]

The reason Cheshvan and Kisleiv are interchangeable: The reason that the two months of Cheshvan and Kisleiv do not follow the set pattern is because of the Molad. The Molad is not exactly 29.5 days, but is 29 days 12 hours and 44 minutes. Now, if we would make six months of the year Malei and 6 months Chaseir it would cause the Molad to fall 44 minutes later each month. This would eventually cause the Molad to fall many days after Rosh Chodesh and the entire proximity of the Molad to Rosh Chodesh would be lost. Because of this surplus of minutes to the Molad we need to have some years contain 8 Malei months, and some years contain 8 Chaseir months and some years contain an equal amount of Malei and Chaseir months.[3] Another reason for the interchangeable months of Cheshvon and Kisleiv is to allow the calendar to position Rosh Hashanah on its proper day of the week. In Halacha F-G we will learn that Rosh Hashanah can never fall on Sunday, Wednesday and Friday, and cannot fall on the Molad Zakein. If we set the two months of Cheshvan/Kisleiv to always follow the pattern of Kesidron or to always be either both Malei or both Chaseir, then it would cause Rosh Hashanah to fall on one of the undesirable days.[4]

Determining whether Cheshvan/Kisleiv is Shaleim/Chaseir/Kesidran:[5] There are various methods that can be used to determine the patterns of the months of Cheshvan and Kisleiv. One method is by determining the number of weekdays between the falling of the previous Rosh Hashanah and the falling of next year’s Rosh Hashanah. If it is a non-leap year and there are four weekday’s in-between the two Rosh Hashanahs then the two months are Malei. If there are three weekdays in-between then the two months are Kesidran, and if there are two weekdays in-between the two months are Chaseir. If it is a leap year and there are four weekdays in-between then the two months are Chaseir. If there are five weekdays in-between then the two months are Kesidran, and if there are six weekdays in-between then the two months are Malei.[6] Another method of calculation [which is the same form of calculation to determine the next years Rosh Hashanah] is to take the weekday of last Rosh Hashanah and by a non-leap year to add two, three, or four weekdays to that day to determine next year’s Rosh Hashanah. If any of the added days falls on either Sunday, Wednesday or Friday then it eliminates the possibility of the months following that order of days. This will usually leave us with two possibilities remaining for the months of Cheshvon and Kisleiv. One then sees if any of the remaining two possibilities cause Rosh Hashanah to fall on the Molad Zakein, or prior to the Molad, and if it does then that possibility is also eliminated, thus leaving us with only one possibility for the order of the months of that year.[7]

The list of the Malei and Chaseir months:[8]

Month 29/30
Tishrei 30
Cheshvan Variable
Kisleiv Variable
Teves 29
Shevat 30
Adar 29
Adar 1 30
Adar 2 29
Nissan 30
Iyar 29
Sivan 30
Tamuz 29
Av 30
Elul 29

 

Always Malei [30 days] Always Chaseir [29 days] Interchangeable
Tishrei Teves Marcheshvan
Shevat Adar Kisleiv
Nissan Iyar  
Sivan Tamuz  
Av Elul  
Adar 1 Adar 2  

[1] Rambam ibid 8:5-6; Tur 428; Understanding the Jewish calendar chapter 12-13

[2] Rambam ibid; Tur 428

[3] Tur 427

[4] Tur 428

[5] Rambam ibid 8:7

[6] Rambam ibid 8:8; Tur 428

[7] See Tur ibid and Understanding the Jewish calendar chapter 13

[8] Rambam Kiddush Hachodesh 8:5-6

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