Astronomical Institutes of Prague Universities in 1882–1945 P. Hyklová and M. Šolc Charles University in Prague, Faculty of Mathematics and Physics, Prague, Czech Republic. Abstract. In 1882, the Prague Charles–Ferdinand University (Universitas Carolo– Ferdinandea Pragensis) was divided into two national universities — German and Czech. Astronomical institutes at both new universities were established, and they operated independently until the end of World War II when the German Charles University in Prague (Deutsche Karlsuniversität in Prag) was abolished. This article summarizes the development of astronomical research at both universities during this period, its institutionalisation and biographies and mainly scientific activities of astronomers, based on the sources from archives of these institutions. Introduction In 19 th century the Prague university, founded in 1348 by Charles IV and reconstructed in 1654 by Ferdinand III to Prague Charles–Ferdinand University (Universitas Carolo–Ferdinandea Pragensis), became bilingual. The tension between German and Czech speaking students and staff members resulted into a split in the year 1882. The observatory in the tower of the Clementinum College (erected 1722 and rebuilt 1751–1755) was attached to the German Charles–Ferdinand University (k.k. deutsche Karls–Ferdinands-Universität) and served as its Astronomical Institute (GeAI), under the leading of Ladislaus Weinek. After World War I, the Clementinum tower and adjacent rooms became the State Observatory of the new Czechoslovak Republic. The newly established German Charles– Ferdinand University incorporated the GeAI which existed until the end of World War II. The GeAI operated observatories in Tellnitz (today Telnice, district Ústí nad Labem) (1929–1945) and Ondřejov (1943–1945). The beginnings of the Astronomical Institute of Czech university (CzAI) proceeded in two steps — the first being the appointment of August Seydler the Professor of Theoretical Astronomy and Theoretical Physics in 1885, and the other step his suggestions to establish the institute on 1886. Even if the foundation decree was missing or not existent, since 1 st January 1887 Seydler led the inventory of the “Provisional Astronomical Institute of the Bohemian Charles–Ferdinand University of Prague”, how he named his institute. Hence we date the origin of CzAI to the preceding year 1886. The existence of this institute (in some periods under slightly different names) continues until now, remarkably without interruption after the 17 th November 1939, when the Czech colleges were closed. In 1890, the Czech university had 3 faculties, 122 staff members, 2195 students, and the German university had 4 faculties, 147 staff members and 1458 students. In the period 1882–1945 several dozen students graduated in astronomy at both universities. German Astronomical Institute 1882–1918 The astronomical observatory at Clementinum College was rebuilt to the present status in ca. 1751–1755, under the first director Joseph Stepling (1716–1778), Jesuit mathematician and physicist. The records of his meteorological and astronomical observations unfortunately disappeared, like another documents from the observatory, due to the abolishment of Jesuit Order in 1773 and secularization of the university. Clementinum, situated in the centre of the city, soon became unsuitable for almost all types of observations. Karl Hornstein (1824–1882) who was director since 1867 decided to leave the purchased instruments in shipping boxes and to carry out only the necessary observations for timekeeping and meteorological service. He influenced joining Clementinum observatory to the German university, but died there in 1882. The renaissance of scientific work, both theoretical and observational, came with the next director Ladislaus Weinek, who gained international recognition for his lunar photographic atlas and participation on the discovery of the effect called “polar motion.” Under the next astronomers, Rudolph Spitaler and Adalbert Prey, the work never comprised such a broad spectrum, although the last head, Erwin Finlay–Freundlich, intended far-reaching projects before he was forced to emigrate. 354 WDS'14 Proceedings of Contributed Papers — Physics, 354–360, 2014. ISBN 978-80-7378-276-4 © MATFYZPRESS