Zach Xavér Ferenc János, Baron

* Bratislava, 13/14 June 1754 – † Paris, 3/4 September 1832 / astronomer, geodesist, corresponding member of the Hungarian Academy of Sciences (1832) ; ; younger brother of Antal Zach. Between 1764 and 1770 he studied at the Piarist order's gymnasium in Veszprém. In 1773 he was a student at the order's College of Natural Philosophy in Pest. He graduated from the Military Engineering Academy in Vienna. After that he was appointed as a mathematics teacher at the University of Lemberg. Under the leadership of Joseph Liesganig (1719–1799), he participated in the determination of the geographical points that were designated for the preparation of the map of the Austrian Empire. This is probably where the irresolvable antagonism that developed between Zach and Liesganig, and more generally Zach and the Jesuits, began, and from which he was never able to get rid of in his life. His university career in Lemberg was ended by an imperial decree, when Joseph II. in 1780, for reasons of economy, terminated Zach's teaching position. From Lemberg he then traveled to Paris, where he became acquainted with, and even befriended, the greatest scientists of the time, including Jerome de Lalande (1732-1807) and Pierre Simon Laplace (1749-1827). The next stop in his life was London, where from 1783, on the recommendation of de Lalande, he received accommodation and work in the house of the Saxon ambassador in London, Count Hans Moritz von Brühl. He gained real fame when he went to a castle in England, where he was shown the mysterious notes of Thomas Harriot (1560-1621). ; After careful study of the subscripted number lines, Zach realized that they contained precise observations of an earlier appearance of Halley's Comet (1607). Zach published his interpretation in the Astronomisches Jahrbuch. He later joined the court of Duke Erwin II of Saxe-Gotha. The prince was an enthusiastic amateur astronomer and commissioned Zach to build a new observatory in Seeberg. He was the director of this astronomical observatory from 1787 to 1806. Here he convened the first international astronomical meeting in 1798 to discuss cooperation between European astronomers, the question of a uniform time system, and the search for a planet (then unknown) supposed to lie between Mars and Jupiter. From 1801 he devoted much attention to the study of asteroids. From 1815 he lived in Genoa: the observatory there was built under his leadership. In 1827 he moved to Paris. In 1796 he founded the first international astronomical journal, the Allgemeine geographische Ephemerident and the Monatliche Correspondenzet, which he edited in Gotha until 1813. In it he published several reports on Hungarian astronomical and geodetic work. Unfortunately, he also caused a lot of damage to the reputation of Hungarian astronomers and astronomy, thus coming into conflict with Miksa Hell (®Hegybánya), about whom he published false news derogatory about his person, and also with his former friend, János Pasquich. He wrote many astronomical works in French. His instrumental and biographical studies are valuable, he was the first to advocate the regular observation of variable stars. A lunar crater bears his name. ; ; His main works: ; Novae et correctae tabulae motuum solis, 1797.