This article originally appeared in the Jewish Free Press, Calgary

The First Rabbi on the Moon*

News Item:

1991--The comet Levy is visible in the night sky. A more famous comet named for the same American astronomer [Levy-Shoemaker 9] would later attract much attention when it dramatically collided with Jupiter in July 1994.

When a report in the Calgary Herald a few months ago announced the arrival of the comet Levy, my personal ethnocentric reaction was one of appreciation that a comet had been given such a fine Hebrew name. As it turned out, the comet was named for its discoverer David Levy, an amateur astronomer who used to live in Canada, but now scans the skies from his backyard in Tuscon, Arizona.

A Blessing for Comets

Comets have long been of interest to Jewish sources. The Mishnah prescribes a blessing for their sighting. The talmudic sage Samuel, a noted astronomer of his day, claimed that though he was as familiar with the paths of the heavens as with the streets of his home town of Nehardea, he felt himself ignorant in the face of the mysteries of the comets.

The name "Levy" has been given not only to a comet, but also to a crater on the moon; and not any ordinary Levy, but a "Rabbi Levi" no less! I presume that the crater in question was named after the 14th-century French Rabbi Levi ben Gershom known to Jews as "Ralbag" and to other as "Gersonides," "Magister Leo Hebreus" or "Maestre Leo de Bagnols." Ralbag is known for his popular commentaries on the Bible. Students of Philosophy know him better for his vigorous critique on various views of Maimonides and Aristotle, a critique which eventually paved the way for the radical views of Spinoza.

Jacob's Staff

The scientific world has recognized Rabbi Levi's important contributions to the fields of mathematics, astronomy and navigation. This summer I had occasion to see some examples of his scientific creations in a remarkable exhibition held in Montreal entitled "Planets, Potions and Parchments." This exhibition presented a rich assortment of books and artifacts illustrating the Jewish involvement with science from the Dead Sea Scrolls until the eighteenth century. The excellent catalogue of the exhibition is available at a number of Calgary book stores, and makes fascinating reading for anyone interested in either science or Judaica.

Visitors to the exhibition were given the opportunity to operate an instrument known as the "Jacob's Staff," a surveying tool consisting of a long rod with sliding plates, used to calculate angular distances with reference to the stars. Credit for the invention of the "Jacob's Staff," which became a necessary aid to medieval sailors, was claimed by Gersonides, who placed great emphasis on the need for empirical observation as a basis for astronomical research.

Gersonides' observations caused him to raise serious criticisms against the prevailing astronomical theories of Ptolemy as regards the motions of the moon and the earth. These objections would eventually result in Copernicus' complete overthrow of traditional astronomical theory. These contributions were recognized in the naming of a lunar crater in Gersonides' honour.

The Science of Astrology

As with many medieval astronomers, Gersonides was a confirmed believer in the scientific validity of astrology. Appropriately, the Rabbi Levi crater on the moon can enjoy the company of another rabbinic crater, also named for a Jewish sage with an appreciation for astrological matters: Rabbi Abraham Ibn Ezra. The twelfth-century Ibn Ezra, who hailed from "Golden Age" Spain, loved to offer astrological explanations for Scriptural passages. He saw an astrological significance to the timing of the religious festivals, and compared the High Priest's jewelled breast plate to the astrolabe, which made it a useful instrument for charting the future.

For Jews astronomy was rarely a mere academic interest. Some familiarity with the courses of the sun and moon was essential for proper observance of time-defined commands such as daily prayers and the holiday calendar. These calculations could be very complicated.

Some years ago Yale University Press sponsored a translation of Maimonides' code of Jewish law, the Mishneh Torah. When the translators came to the section dealing with the rules for calculating the Hebrew calendar, they realized that this was no simple job of translation, but required specialized knowledge of mathematics and astronomy. One thing led to another, and in the end the short treatise had to be released as a separate volume with learned appendices by distinguished scientists.

The Jewish interest in astronomy has been a long and fruitful one. When the first Jew arrives on the moon he will hopefully feel that this too is, in some way, territory trodden by his ancestors.

This article and many others are now included in the book

Why Didn's I Learn This in Hebrew School?Why Didn't I Learn This in Hebrew School

by Jason Aronson Publishers

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First Publication:

  • JFP, July 2 1991.


  • B. Barry Levy, Planets, Potions and Parchments: Scientific Hebraica from the Dead Sea Scrolls to the Eighteenth Century, Montreal & Kingston 1990.