Jewish Leap Years: A Halachic and Hashkafic Approach

And this matter is a law of Moses from Sinai: That at a time that there is a Sanhedrin, we set [the new month] by sighting; and when the Sanhedrin does not exist, we set [it] according to this calculation that we [use] to calculate today, and we are not concerned about the sighting...

(1) The months of the year are lunar months, as it is stated (Numbers 28:14), "the monthly burnt-offering for each new moon"; and it is [also] stated (Exodus 12:2), "This month shall be for you the beginning of the months." Thus did the Sages say: The Holy One, blessed be He, showed Moshe a likeness of the moon in a prophetic vision and said to him, "See [when] it is like this, and sanctify it (as the beginning of the month)." But the years that we calculate are solar years, as it is stated (Deuteronomy 16:1), "Guard the month of the Spring."

(2) The solar year exceeds the lunar year by eleven days, approximately. Hence, whenever this excess accumulates to about thirty days, somewhat more or less, one month is added and the year is made up of thirteen months and is called leap year. The year cannot consist of twelve months plus several days, because it is written: "Months of the year" (Exodus 12:2), implying that the year should be reckoned by months and not by days.

(1) A leap year is a year to which an extra month is added. Only Adar is the month that is ever added, so that a leap year has two months of Adar: a first Adar and a second Adar. Why is just this month added? Because of the spring season, so that Pesaḥ should be observed during the barley season, as it is written: "Observe the month of Aviv, and keep the Passover…" (Deuteronomy 16:1), implying that this month of Nisan should occur during the spring. Without the addition of this month of Adar, Passover would occur sometimes in the summer and sometimes in the rainy season [of winter].

(20) Mordecai recorded these events. And he sent dispatches to all the Jews throughout the provinces of King Ahasuerus, near and far, (21) charging them to observe the fourteenth and fifteenth days of Adar, every year— (22) the same days on which the Jews enjoyed relief from their foes and the same month which had been transformed for them from one of grief and mourning to one of festive joy. They were to observe them as days of feasting and merrymaking, and as an occasion for sending gifts to one another and presents to the poor.

MISHNA: If the people read the Megilla during the first Adar and subsequently the year was then intercalated by the court and now the following month will be the second Adar, one reads the Megilla again during the second Adar...

(1) The day of the 14th and the 15th of the First month of Adar [in a leap year] we do not fall upon our faces [recite tahanun] and we do not say (the Psalm) a song - Hashem will answer you on a day of suffering, and on them [the 14th and 15th of Adar I] it is forbidden to eulogize or fast. There are those who say that even eulogies and fasting is permitted. Rema: the practice is according to the first understanding. There are those who say that one is obligated to increase in joy and feasting on the 14th of Adar I however this is not the practice. Nonetheless one should increase slightly their joy and feasting in order to fulfill the words of those who are stringent 'But he that is of a merry heart hath a continual feast (Proverbs 15:15).'

In explaining this commandment the sages taught thus: Even as He is called gracious, be thou gracious; even as He is called merciful, be thou merciful; even as He is called holy, be thou holy.⁴Shabbat, 133b.; Sotah, 14a. C. In this wise did the prophets attribute to God all such terms as long-suffering, abundant in benificence, just and right, perfect, mighty and powerful and others like these, to proclaim that they are good and straight paths, and that man is obligated to lead himself in them, and to be like unto Him in proportion to his power.