Gans (1541–1613), a chronicler, astronomer, and mathematician, was born in Lippstadt, Westphalia. He studied rabbinics with the rabbis noted above, and is said to have been encouraged, by Rema, to study mathematics and astronomy. In the house of his first father-in-law Gans apparently found a Hebrew translation of Euclid by Moses ibn Tibbon; his second father-in-law was the physician Samuel Rofe who had become famous for his mercury cures of syphilis. Gans was one of the few German Jews of his time, when rabbinics ruled supreme, to undertake serious secular studies for which he found and quoted older Jewish authorities. In Prague he corresponded with the astronomer Johann Mueller (Regiomontanus) and was in friendly contact with Johann Kepler and Tycho Brahe, for whom he translated the Alfonsine Tables from Hebrew into German.

Gans's main astronomical (and also geographical) work was Nehmad ve-Na'im ("Delightful and Pleasant," Jesnitz, 1743; shortened version Magen David, Prague, 1612) in which he rejects the new Copernican system in favor of Ptolemy's, the former going back (according to Gans) to the Pythagorean system. Astronomy (and mathematics)—he held—was first studied by Jews from whom the Egyptians had learned the science, passing it on to the Greeks. Ptolemy had studied with Alexandrian Jewish scholars. The study of astronomy was important not only for the Jewish calendar but as proof for the cultural achievements of the Jewish people. Other works by Gans on mathematics, the calendar, and the geography of Erez Israel remained unpublished. Gans wrote his chronicle Zemah David ("Offspring of David," Prague, 1592) in two parts, one dealing with Jewish history to the date of publication, the other with general history. He had written it for "householders like myself and of my worth," while justifying the inclusion of general history by the fact that it contained ethical teachings of emperors, which ordinary people would accept coming from such illustrious mouths. The first part of the work summarizes that of his predecessors, such as Ibn Daud and Zacuto, but he dissociates himself from the untraditional approach of Azariah dei Rossi. For the second part his sources are contemporary German chroniclers like Cyriak Spangenberg and Laurentius Faustus, though in his introduction he expresses doubts as to their reliability. Gans shows an interest in economics; his description of historical events and situations reflects the spirit and taste of the 16th-century Jewish "householder" in Bohemia and Poland. The Zemah David remained a standard work up to the Haskalah period. The second edition by David b. Moses of Reindorf (Frankfort, 1692) brings the chronicle up to the date of publication, also giving a long poetical description of the Fettmilch riots of 1614. It was translated into Latin by W. H. Vorst (Leyden, 1692); into Yiddish by Solomon Zalman Hanau (Frankfort, 1698); and parts of it into German by G. Klemperer (ed. Moritz Gruenwald, 1890). The Warsaw edition of 1849, also brought up to date, was reproduced in 1966 with introductions in Hebrew and English and an index.