A Lesser known contemporary of Tycho Brahe and Johannes Kepler 

It is generally thought that Jews  made no contribution to the advancement of the natural sciences during the middle ages and the Renaissance. The reason for this is that Jew's lives were precarious in those days due to rampant religious persecution and the general instability in Europe in those days.  Jews had no time for scientific pursuits because they had to struggle for survival or were constantly on the move.

One exception to this is David Gans a contemporary of Galileo and Kepler, who was a Talmud scholar historian, mathematician, astronomer and geographer.

He was born in Lippstadt, Germany in 1541 (died 1613). He was educated in Bonn and Frankfurt by famous talmudist teachers and attended the yeshiva in Cracow that was headed by Moses Isserles. Isserles encouraged Gans to study philosophy, mathematics, astronomy, geography, and history. He came to Prague in 1564 and was taught by two brothers Sinai ben Bezalel and Jehuda ben Bezalel also known as Rabbi Loew and as the Maharal of Prague (the legendary rabbi who was supposed to have conjured up the Golem). In the late 1560’s, Gans studied Euclidian geometry and mathematics in Nordheim. Because of the relatively peaceful and tolerant atmosphere enjoyed by the Jewish 
community in Prague at the end of the 16^th century and the beginning of the 17^th century, outstanding Jews were allowed to have contact with the Christian community. David Gans established contact with Tycho Brahe and his assistant Johann Müller as well as with Johannes Kepler.

In his book Nehmad ve-naim (“The Pleasant and the Dear” written in Hebrew), Gans reports that he participated in three different observations made in Tycho Brahe’s observatory in Benátky nad jizerou and that he had translated the Alphosine tables from Hebrew into German. The Alphosine tables were created in 1252 upon commission by Alphonso X of Castile in Toledo Spain. These were tables used to determine the positions of the sun, moon, and the planets relative to the fixed positions of stars. Interestingly Gans also knew of the work of Copernicus (concerning the heliocentric theory stating that the sun and not the earth was the center of the solar system). Gans however preferred the system of Ptolemy with an earth centered solar system (Ptolemy was educated by Jewish teachers in his day).

The Nehmad ve-naim is considered to be a unique book written by a Jewish Ashkenazi author of that time that summed up all existing knowledge by both Jewish and non-Jewish scholars on geometry, astronomy, and mathematical geography. It is interesting to note that the book was written during a time of relative conservatism among Central European Jews at that time. His book however remained neglected and was not printed until the 18the century.

David Gans is perhaps best known for his historical work "Zemach David" (the Wand of David) which consisted of a history of the Jews from biblical times till 1592 (considered by him as the sacred part), and a more general history of the world. Also interesting in this work is that it presents a summary of the humanities during the Renaissance from the point of view of a Jewish scholar.

It is a stroke of luck that we know about David Gans and his accomplishments making him an exception to the rule that Jews did not contribute to the advancement of knowledge in the natural sciences in the middle ages. I would suggest that he is at the tip of an ice berg of possibly many more unknown heroes in science.

Source:

RyBar Citibor. 1991 TV Spektrum in cooperation with Akropolis Publishers Jewish Prague (Notes on History and Culture, A Guidebook). pp 155-159