Collegium Helveticum Semper-Sternwarte Zürich

Schmelzbergstrasse 25, 08092 Zürich Map
Wed-Sat 2-6 pm

ETH Zurich’s old Swiss National Observatory (Semper Observatory)

The observatory building has strong ties to mathematician and astronomer Rudolf Wolf (1816–1893), who accepted a professorship at the newly founded Zurich Polytechnic in 1855, and professor of architecture and Head of the Zurich Polytechnic’s school of construction Gottfried Semper (1803–1879). In parallel to the construction of the polytechnic between 1859 and 1864, Wolf had an observatory built according to Semper’s designs. The Swiss government bore the costs of construction and the canton of Zurich provided a plot of land for the observatory located in the former Oberstrass municipality (which was incorporated into the city of Zurich in 1893). The observatory’s dome was built by the company Escher Wyss according to the designs and specifications of Wolf and Franz Reuleaux (1829–1905), a German professor of mechanical engineering. After three years of construction, the observatory opened its doors in 1864, eventually housing both the Swiss astronomical and meteorological institutes on the second floor until 1881.

Under the leadership of its first director, Rudolf Wolf, the observatory became a long-standing, internationally renowned centre for the study of sunspots. Later, its astronomers went on to coordinate the observation of sunspots on an international level, and also devised the Zurich Sunspot Number. Throughout its history (1863–1980), the observatory was led by four different directors: Rudolf Wolf (1864–1893), Alfred Wolfer (1894–1926), William Otto Brunner (1926–1945) and Max Waldmeier (1945–1979).

Over the past 150 years or so, the observatory has undergone extensive renovation work.  The so-called Kleine Observatorium (‘Little Observatory’) was built around the edge of the observatory’s observation deck between 1910 and 1911. The solar observation tower followed in 1950–51, while the area to the north between the observatory and the canton pharmacy was redeveloped between 1989 and 1993.

During the planning phase of construction for the canton hospital in 1928, restrictions on the height of surrounding buildings were lifted. Over the years, the erection of new hospital buildings therefore severely affected the use of astronomical instruments positioned at ground level. Further serious disruption to the observatory’s work arose due to the new district heating plant (1933), the extension of the Zurich Institute of Chemistry (1937) and, from 1945, the new canton hospital – the present-day University Hospital of Zurich. Further development of the area surrounding the observatory (the construction of the canton’s gynaecological hospital, 1970–1979) – and the subsequent increase in emissions – soon threatened the building’s location on Schmelzbergstrasse, leading it to close its doors on 1st April 1980. After that, the premises went on to house the Department of Microtechnological Wood Research.

Following a cantonal government decision in 1981, the list of national monuments under conservation was extended to include the city of Zurich, thus bringing the observatory under government protection as a listed building. At the same time, the observatory was recognised as a building of national importance. Following extensive restoration work (1995–1997), the observatory has been home to the Collegium Helveticum since 1997.