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The Book against the People of the Equinox: T-S K6.63

Nadia Vidro

How to fix the calendar was one of the most prominent issues of contention between medieval Rabbanites and Karaites. Whereas Rabbanites used fixed mathematical schemes for determining months and intercalating years, Karaites relied on the observation of natural phenomena, such as the appearance of the new crescent moon and the ripening of the barley (aviv).

However, Karaites themselves had no uniform opinion on calendar matters. The procedure of intercalating the year and determining the date of Passover on the basis of the barley crop was rooted in the biblical commandment to observe the month of aviv and celebrate Passover (Deuteronomy 16:1). However, it involved many unknown quantities that could not be unambiguously established on the basis of the biblical text. While all Karaites agreed that aviv referred to barley in a certain stage of ripening, they held different opinions about the exact ripening stage that one was to look for, the time and place of the investigation, and the amount of crops in the correct stage of ripening that had to be present in order to celebrate Passover.

Some Karaites in Iraq preferred a different method altogether. Instead of the barley crop in the state of aviv, they relied on the vernal equinox as a criterion for celebrating Passover, defined as the time when the sun enters the constellation of Aries. Their arguments against the aviv and in favour of the equinox are known from a legal work on the commandments composed by the Karaite Levi b. Yefet.[1]

These so-called “people of the equinox” met with opposition from Jerusalem scholars associated with the Karaite Academy (dār lil-ʿilm) in that city. One of the scholars who wrote against the equinox method was Abū Yaʿqūb Yūsuf ibn Ibrāhīm al-Baṣīr (Heb. Joseph ben Abraham ha-Roʾeh; b. in 960s or 970s, d. between 1037 and 1039).[2] Originally from Persia or Iraq, Yūsuf al-Baṣīr moved to Jerusalem at the end of the 10th century and became one of the most brilliant members of the Karaite Academy, whose works belong to what is now known as the Golden Age of Karaite literature.

Al-Baṣīr’s polemical treatise against the supporters of the equinox was known from mentions in his other works but never previously identified. Recently, I came across a title page and introduction of this work in T-S K6.63. A search for joins on the Friedberg Jewish Manuscripts Society’s platform quickly revealed that additional fragments of the work are found in T-S Ar.50.121, T-S AS 154.512, and T-S Ar.28.36. The fragments are on parchment in an 11th-century hand and refer to al-Baṣīr as deceased, suggesting that they were copied not long after his death.

title of image here


T-S K6.63 verso

אלכתאב עלי אצחאב

אלאעתדאל ללשיך

אבו יעקוב יוסף בן אברהם

אלבציר נו֗ נפ֗

Book against the people

of the equinox by the Šaykh

Abū Yaʿqūb Yūsuf b. Abraham

al-Baṣīr, may his soul be at rest


title of image here


T-S K6.63 recto

למא ראית אידך אללה שתאת

אלנאס פי אמר אלעיד לאגל

תאכר אלאעתדאל ען וגוד אלאביב

ותעויל בעצ֗הם עליה סאלתנא

אמלי כלאם פיה ואלאגתהאד

פי איצ֗אח שבההם וחלהא

פאגבתך אלי סואלך מע מסלתה

תעאלי אלעצמה מן כל גלט וזל[ל]

והו אלמתפצ֗ל באגאבה דלך

בלטפה וכרמה

When you, may God support you, saw the disunion

of the people in the matter of the festival due to

the equinox falling after the finding of the aviv

and to some people’s relying on it, you asked us

to dictate a discourse about it and to take pains to

make plain their errors and undo them.

We have responded to your request, while asking

the Exalted One to guard us from all errors and mistakes.

He is the One who is gracious in responding to this

in His benevolence and generosity.



From this introduction one can learn that Yūsuf al-Baṣīr composed The Book against the People of the Equinox at the request of someone who had noticed people celebrating Passover at different times due to their reliance on the equinox instead of the aviv – noticeable on those occasions when these two phenomena do not co-occur. Composing a book in response to a questioner is a trope in medieval Arabic introductions[3] but the calendrical concern must have been real. The questioner was particularly troubled about years when the vernal equinox occurred after the aviv had been found and Passover celebrated by those relying on it. In such cases those relying on the equinox would not have celebrated with the rest of the Karaites but would have intercalated the year and celebrated Passover in the next month, ensuring that Passover fell in the spring season as marked by the vernal equinox.

Two questions arise in connection with the identified fragments. Firstly, what method did the “people of the equinox” use to establish when the equinox occurred? Various values could be found in Muslim astronomical tables and the traditional Jewish calculation of tequfat Šemuʾel must have been known to Iraqi Karaites, too. It has, furthermore, been suggested that they may have observed rather than calculated the equinox.[4] At this stage of my research it is unclear which values they used. Yūsuf al-Baṣīr himself highlighted the existence of different values as a weakness of the equinox method when referring to it in his legal work Kitāb al-Istibṣār. He pointed out that the time of the equinox could not accurately be known since the values given in the astronomical tables (zīj) of Ptolemy and of al-Maʾmūn are not the same and the Rabbanite tequfa differs from them both.[5]

Secondly, it is not clear whether Iraqi Karaites were the only group of people who Yūsuf al-Baṣīr polemicised against. On the one hand, his exposition appears from the surviving fragments to tackle the Iraqis’ arguments in favour of the equinox as they are found in Levi b. Yefet’s book. On the other hand, T-S Ar.28.36v mentions Saʿadya Gaon and T-S Ar.28.36r cites BT Sanhedrin 11b, two pronouncedly Rabbanite sources. In BT Sanhedrin 11b the ancient empirical rabbinic intercalation procedure is described, which was based on three criteria – the aviv, fruits of the tree and the equinox. Unlike the empirical Talmudic calendar, the calculated Rabbanite calendar used in the time of Yūsuf al-Baṣīr, as well as today, does not depend on the equinox. Notwithstanding this, it seems possible that Yūsuf al-Baṣīr subsumed Rabbanites under the “people of the equinox” for the purposes of his polemic.[6]


Research for this Fragment of the Month was supported by a grant from the Fritz Thyssen Foundation, 'Qaraite and Rabbanite calendars: origins, interaction, and polemic'. 


[1] Levi b. Yefet, Book of Commandments, completed in 1006/1007 (Oxford, Bodl., Reggio 5, fols 16r-16v). 

[2] Gregor Schwarb, “Yūsuf al-Baṣīr”, in: Encyclopedia of Jews in the Islamic World, Executive Editor Norman A. Stillman. Consulted online on 26 July 2019

[3] Freimark, Peter. Das Vorwort Als Literarische Form in Der Arabischen Literatur, Münster, 1967, pp. 36–37

[4] Haggai Ben Shammai, conference paper “Levi ben Yefet on the calendar - revisited” at the Research Workshop “Karaite Studies:  The State of the Field”, Ben-Gurion University of the Negev, Israel, February 2012. A video recording of the talk is available at (accessed on 2 August 2019; link opens in new window)

[5] Kitāb al-Istibṣār fī al-farāʾiḍ, discourse 3, chapter 4, see Ms. SP RNL Evr.-Arab. I 1793, fol. 104a.

[6] In his Book of Commandments, Levi b. Yefet states that the Rabbanite calculations is “close to the equinox” (Oxford, Bodl., Reggio 5, fols 16r).

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