Who makes the Jewish calendar?

(5) God called the light Day and called the darkness Night. And there was evening and there was morning, one day.

(14) God said, “Let there be lights in the expanse of the sky to separate day from night; they shall serve as signs for the set times—the days and the years; (15) and they shall serve as lights in the expanse of the sky to shine upon the earth.” And it was so. (16) God made the two great lights, the greater light to dominate the day and the lesser light to dominate the night, and the stars. (17) And God set them in the expanse of the sky to shine upon the earth, (18) to dominate the day and the night, and to separate light from darkness. And God saw that this was good. (19) And there was evening and there was morning, a fourth day.

(2) On the seventh day God finished the work that had been undertaken: [God] ceased on the seventh day from doing any of the work. (3) And God blessed the seventh day and declared it holy — having ceased on it from all the work of creation that God had done.

(1) ה' said to Moses and Aaron in the land of Egypt: (2) This month shall mark for you the beginning of the months; it shall be the first of the months of the year for you.

החודש הזה לכם ראש חדשים, from now on these months will be yours, to do with as you like. This is by way of contrast to the years when you were enslaved when you had no control over your time or timetable at all. While you were enslaved, your days, hours, minutes even, were always at the beck and call of your taskmasters.

ראשון הוא לכם, if not for this line I might have thought that when we have a leap year we should add an additional month of Nissan instead of an additional month of Adar. This would not work as the month of Nissan would also be the second month during that year. The Torah said specifically that the month of Nissan is to be (only) the first in a list of months. It did not distinguish between a year that has 13 months and a year that has twelve months. The Torah nowhere warned us against having a year of thirteen months (or more). The Torah decreed to offer the Passover during that month and called it “the first month.” It also decreed that at least part of the festival must occur during the season known as “spring,” i.e. after the spring equinox. It also decreed that the festival of Shavuot, 50 days after the beginning of Passover must occur during a season when wheat is already being harvested. [when the the first ripe fruit of the seven species for which the land of Israel is famous, may already be ready to be offered in the Temple.]

(1) ה' spoke to Moses, saying: (2) Speak to the Israelite people and say to them: The fixed times of ה', which you shall proclaim as sacred occasions - these are My fixed times. (3) On six days work may be done, but on the seventh day there shall be a sabbath of complete rest, a sacred occasion. No work shall you do; it shall be a sabbath of ה' in all of your settlements. (4) These are the set times of ה', the sacred occasions, which you shall proclaim at their appointed times.

Regulate the festive seasons in so that Israel will become knowledgeable in them [their observance]. Hence we derive the law that they (the Sanhedrin) proclaim a leap-year (i. e. intercalate a second Adar) for the sake of those living in the diaspora who have already left their homes in order to go up for the festival but have not yet arrived in Jerusalem (Sifra, Emor, Section 9 1; cf. Sanhedrin 11a).

It seem that we must understand this verse in the following manner: In the first instance G'd informed the Jewish people that in principle the exact time (though not the calendar date) of these "appointed seasons" are subject to input by the Sanhedrin, the Jewish Supreme Court.

In view of this principle, the Torah feared that we might err and believe that even the Sabbath itself was subject to such input by the Sanhedrin, i.e. to postponement if it suited the court. The Torah therefore wrote: "these are My appointed seasons, you are to have work performed for six consecutive days and only the seventh day is the Sabbath on which you may not perform all manner of work."

The Torah had to write once more: "these are the appointed seasons of the Lord which you are to proclaim," to inform us that we are entitled to adjust the part of the calendar dealing with those days to suit our needs. This is followed by the respective dates in the first month, the third month and the seventh month which are liable to be affected by adjustments made by the Sanhedrin.

There may be yet another reason why the Torah repeated the formula אשר תקראו אותם, "which you are to proclaim (or may) proclaim." Maimonides writes as follows in chapter 4 of his treatise on the sanctification of the new month: "There are three considerations which justify lengthening the year by means of the insertion of an extra month:

1) Bringing it in line with the solar seasons of the year.

2) Ensuring that Passover occcurs in the spring as demanded by the Torah.

3) Enabling the period when the fruit of the trees ripen to occur in summer.

Maimonides mentions some other reasons which may prompt the Sanhedrin to adjust the calendar, such as to enable travellers to make their pilgrimage to Jerusalem at a time when the roads are passable, etc., or at a time when the bridges are safe from flooding, etc.

The secondary reasons are mostly connected to the fact that many Israelites lived in the diaspora.

In other words, the two principal considerations for adjusting the calendar are A) climate-related reasons. B) people-related reasons.

Seeing that the Torah described the Passover festival as occurring in the season of the spring, the religious authorities made the necessary adjustments to conform with this requirement. The Torah repeats the right of the Sanhedrin to proclaim when these dates should occur in order for us to know that both climate-related considerations and people-related considerations are valid reasons for the Sanhedrin to make use of its authority in this regard.

In six months of the year the messengers go out from the court in Jerusalem to report throughout Eretz Yisrael and the Diaspora which day was established as the New Moon, the thirtieth or the thirty-first day since the previous New Moon.

• They go out in the month of Nisan, due to Passover, so that people will know on which day to celebrate it;
• in the month of Av, due to the fast of the Ninth of Av;
• in Elul, due to Rosh HaShana, which begins thirty days after the New Moon of Elul;
• in Tishrei, due to the need to establish the correct dates on which to celebrate the Festivals of Tishrei, i.e., Yom Kippur and Sukkot;
• in Kislev, due to Hanukkah;
• and in Adar, due to Purim.

And when the Temple was standing, messengers would also go out in the month of Iyyar due to small Passover.

Only for the sake of two months may witnesses who saw the new moon desecrate Shabbat, should that be necessary in order for them to offer testimony before the court: For the month of Nisan and for the month of Tishrei, for in these months messengers are sent out to Syria, and by them, i.e., these months, the dates of the major Festivals are set: Yom Kippur, Sukkot, Passover, and Shavuot.

And when the Temple was standing, the witnesses desecrated Shabbat for the fixing of the New Moon of all the months, due to the imperative of fixing the proper offering of the New Moon at the correct time.

If the members of the Great Sanhedrin in Jerusalem are not familiar with that one who saw the new moon, i.e., that he is a valid witness, the members of his local court of twenty-three send another with him to testify about him.

The mishna adds: Initially, the court would accept testimony to determine the start of the month from any person, as all are presumed to be qualified witnesses, absent any disqualifying factors.

However, when the Boethusians, a sect whose members had their own opinions with regard to the establishment of the Festivals, corrupted the process by sending false witnesses to testify about the new moon, the Sages instituted that they would accept this testimony only from those men familiar to the Sanhedrin as valid witnesses.

Initially, after the court sanctified the new month they would light torches on the mountaintops, from one peak to another, to signal to the community in Babylonia that the month had been sanctified. After the Samaritans [Kutim] corrupted and ruined this method by lighting torches at the wrong times to confuse the Jews, the Sages instituted that messengers should go out to the Diaspora and inform them of the start of the month.

How do they examine the witnesses who come to testify about the new moon? They deal with them in order, as the pair of witnesses that arrives first they examine first. They bring in the greater of the two witnesses, and they say to him:

Say how you saw the moon. Was it in front of the sun or behind the sun? To its north or to its south? How high was the moon over the horizon, and in which direction did it tilt? And how wide was it?

(If, for example, he said that he saw the moon in front of the sun, he has not said anything of substance, as this is impossible and therefore he is either mistaken or lying.)

And after they finish hearing the first witness’s testimony, they would bring in the second witness and examine him in a similar manner.

If their statements match, their testimony is accepted and the court sanctifies the New Moon.

And the court then asks all the other pairs of witnesses certain general matters, without probing into all the details. They do this not because they require the additional testimony, but so that the witnesses should not leave disappointed, and so that the witnesses should be accustomed to coming to testify, and will not hesitate to come the next time, when they might be needed.

After the witnesses have been examined and their testimony accepted, the head of the court says: "Mekudash/ It is sanctified." And all the people respond after him: "Mekudash! Mekudash! / It is sanctified; it is sanctified."

Whether the moon was seen at its anticipated time, on the thirtieth day of the previous month, or whether it was not seen at its anticipated time, in which case witnesses are not necessary to establish the following day as the New Moon, the court sanctifies it and formally proclaims the day as the New Moon.

Rabbi Elazar, son of Rabbi Tzadok, says: If the new moon was not seen at its anticipated time, the court does not sanctify the New Moon on the following day, as the celestial court in Heaven has already sanctified it, precluding the need for the additional sanctification by the earthly court.

Rabban Gamliel had a diagram of the different forms of the moon drawn on a tablet that hung on the wall of his attic, which he would show to the laymen who came to testify about the new moon but were unable to describe adequately what they had seen. And he would say to them: Did you see a form like this or like this?

There was an incident in which two witnesses came to testify about the new moon, and they said: We saw the waning moon in the morning in the east, and that same day we saw the new moon in the evening in the west. Rabbi Yoḥanan ben Nuri said: They are false witnesses, as it is impossible to see the new moon so soon after the last sighting of the waning moon. However, when they arrived in Yavne, Rabban Gamliel accepted them as witnesses without concern.

And there was another incident in which two witnesses came and said: We saw the new moon at its anticipated time, i.e., on the night of the thirtieth day of the previous month; however, on the following night, i.e., the start of the thirty-first, which is often the determinant of a full, thirty-day month, it was not seen. And nevertheless Rabban Gamliel accepted their testimony and established the New Moon on the thirtieth day. Rabbi Dosa ben Horkinas disagreed and said: They are false witnesses; how can witnesses testify that a woman gave birth and the next day her belly is between her teeth, i.e., she is obviously still pregnant? If the new moon was already visible at its anticipated time, how could it not be seen a day later? Rabbi Yehoshua said to him: I see the logic of your statement; the New Moon must be established a day later.

Upon hearing that Rabbi Yehoshua had challenged his ruling, Rabban Gamliel sent a message to him: I decree against you that you must appear before me with your staff and with your money on the day on which Yom Kippur occurs according to your calculation; according to my calculation, that day is the eleventh of Tishrei, the day after Yom Kippur.

Rabbi Akiva went and found Rabbi Yehoshua distressed that the head of the Great Sanhedrin was forcing him to desecrate the day that he maintained was Yom Kippur.

In an attempt to console him, Rabbi Akiva said to Rabbi Yehoshua: I can learn from a verse that everything that Rabban Gamliel did in sanctifying the month is done, i.e., it is valid. As it is stated: “These are the appointed seasons of the Lord, sacred convocations, which you shall proclaim in their season” (Leviticus 23:4). This verse indicates that whether you have proclaimed them at their proper time or whether you have declared them not at their proper time, I have only these Festivals as established by the representatives of the Jewish people.

Rabbi Yehoshua then came to Rabbi Dosa ben Horkinas, who said to him: If we come to debate and question the rulings of the court of Rabban Gamliel, we must debate and question the rulings of every court that has stood from the days of Moses until now. As it is stated: “Then Moses went up, and Aaron, Nadav and Avihu, and seventy of the Elders of Israel” (Exodus 24:9). But why were the names of these seventy Elders not specified? Rather, this comes to teach that every set of three judges that stands as a court over the Jewish people has the same status as the court of Moses. Since it is not revealed who sat on that court, apparently it is enough that they were official judges in a Jewish court.

When Rabbi Yehoshua heard that even Rabbi Dosa ben Horkinas maintained that they must submit to Rabban Gamliel’s decision, he took his staff and his money in his hand, and went to Yavne to Rabban Gamliel on the day on which Yom Kippur occurred according to his own calculation. Upon seeing him, Rabban Gamliel stood up and kissed him on his head. He said to him: Come in peace, my teacher and my student. You are my teacher in wisdom, as Rabbi Yehoshua was wiser than anyone else in his generation, and you are my student, as you accepted my statement, despite your disagreement.