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The Astronomical Observatory is located in the heart of the Imperial Campus of the University of Strasbourg, on the site of the former Fishermen’s Gate. This complex is part of the urban extension built at the end of the 19th century by the German Empire and has been on the Unesco World Heritage List since 2017.

The architectural and instrumental heritage of the observatory was studied as part of a survey carried out in 2004 by the Inventory and Heritage Department of the Alsace region, in partnership with the Jardin des Sciences. Carried out in close collaboration with the Observatory’s staff, the operation allowed the implementation of a real study, safeguarding and valorisation process.

The results of this survey are available online:
Presentation of the buildings
Inventory of heritage in Alsace – Summary of movable objects

Copyright, unless otherwise stated, Claude Menninger (c) University of Strasbourg – Jardin des sciences / Région Grand-Est – Inventaire général

The Jardin des Sciences also offers tours specifically dedicated to the observatory’s heritage.

For any information about the observatory’s heritage and collections, please contact
Delphine Issenmann, in charge of the inventory and collections

The architectural heritage

The observatory at the heart of the imperial university
The observatory is located at the eastern end of the imperial campus, created following the annexation of Strasbourg by Germany after the Franco-Prussian war of 1870-1871. The latter was the first site of the extension plan, called Neustadt (new city), which, by tripling the surface area of Strasbourg, would make it possible to accommodate the infrastructures necessary for the capital of the new Land of Elsass-Lothringen. Within the university, the observatory took part in this metamorphosis and was a showcase for German progress.

The third Strasbourg astronomical observatory
However, this was not the first establishment dedicated to astronomy: the existence of astronomical observatories in Strasbourg dates back to the end of the 17th century. The city’s first observatory was built in 1673 on the tower of the city walls, at the entrance to the civil hospital. A second observatory was built in 1828 on the roof of the Académie building, which then housed the science and medicine faculties. In 1872, when Alsace was ceded to Germany, Emperor Wilhelm I decided to build a prestigious university and an observatory to promote his empire. The plans for this new observatory, like those for the university’s other scientific institutes, were entrusted to the architect Hermann Eggert, who worked in close consultation with the astronomer August Winnecke to propose a layout that took into account the functional needs of the discipline. Work began in 1877 and was completed in 1880. The astronomical instruments were installed in the winter of 1880 and the observatory was opened on 22 September 1881.

An architecture for science

August Winnecke, the first director of the imperial university’s observatory, drew heavily on the Pulkovo observatory, where he had been trained, to propose a plan based not on a single building, bringing together all the activities, but on three distinct buildings: the Grande Coupole, the meridian observation pavilion and the director’s house, linked by a system of corridors that meet in a rotunda. This arrangement makes it possible to separate in space the functions devoted to observation and those of everyday life in order to limit disturbances. The best possible observation conditions must be guaranteed, especially as the instruments used are increasingly powerful but also sensitive to vibrations, temperature and humidity variations.

In 1919, when Alsace became French again, the director Ernest Esclangon modernised the equipment by installing electricity and wireless telegraphy. He also set up an electrical system to synchronise all the observatory’s clocks.

Today, the astronomical observatory is still a place of research and teaching and has a remarkable architectural heritage. Often symbolised by the Grande Coupole, it is in fact a real complex made up of three main buildings, several small observation buildings spread out over a landscaped site, the layout of which even influences the organisation of the surrounding neighbourhood.

The Grande Coupole

The monumental building of the Grande Coupole houses an equatorial refracting telescope with a diameter of 49 cm and a focal length of 7 metres. Behind its neo-renaissance facades, everything from the foundations to the dome opening system and the elevations were designed to ensure the stability necessary for highly accurate observations.

The hemispherical dome, with a diameter of 12m and a weight of 34 tons, is covered by a double envelope of wood and zinc, inside which are stretched boat sail cloths. It can be opened in all directions by means of two hatches placed on either side of the zenith. The whole structure was completely restored in 1995.

In order to accommodate the increase in staff while maintaining the activity on site, the building was enlarged by almost 500 m2 thanks to the four glass and metal cubes added to each corner of the building in 1998 by the architect Roland Hoenner: one of them contains an amphitheatre and the others are occupied by offices and classrooms.

The meridian building

The meridian building is built in the shape of an L; it takes its name from the two meridian rooms that make it up, originally containing the Cauchoix meridian telescope and the Repsold meridian circle. The north and south domes, located in the western part of the building, housed equatorial instruments: a 16cm telescope and an altazimuth.
The meridian rooms have through openings covered by iron frames and double enclosures allowing the installation of zenithal hatches and high windows to clear the meridian axis for observations. The floors are located five metres above the ground to avoid night observations being altered by the reverberation of the heat accumulated during the day or by the frequent fog in this marshy area. In 1982, the room of the Cauchoix meridian telescope was converted into a planetarium projection room, with the pillar of the instrument serving as a support for the projector.