Sonneberg Observatory

Observatory

Location of Sonneberg Observatory

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Sonneberg Observatory (German: Sternwarte Sonneberg) is an astronomical observatory and was formerly an institute of the Academy of Science in the German Democratic Republic. It is located on the 638 m high Erbisbühl in the Neufang district of Sonneberg. The observatory was founded on the initiative of Cuno Hoffmeister by the town of Sonneberg with the support of the Carl-Zeiss-Stiftung. On 28 December 1925, the observing station with the first domed tower was ceremoniously inaugurated. By 1928 it was expanded significantly and at the time was the highest astronomical observatory in Germany. The observatory, in its astronomy museum, has one of the world's largest collections of photographic plates.^[1] The museum is open to interested visitors, especially amateur astronomers and school students, so as to introduce them to the history and new findings in the fields of astronomy and astrophysics.

History

From 1930, the observatory was leased to the Prussian state and de facto became a branch of the Berlin Observatory at Berlin Babelsberg. Paul Ahnert worked at the observatory for several decades starting 1938. During the Second World War, from 1940 onwards, the observatory was also used as a weather observatory, making it subordinate to the national weather service and hence the Luftwaffe. After the war, Cuno Hoffmeister managed to continue the observatory's research programmes under Soviet occupation. In 1945, however, the occupying power ordered the dismantling of the most powerful telescope – a 40 cm astrograph – for a Soviet observatory, as part of World War II reparations. In April 1946, the Sonneberg Observatory became a research institute of the German Academy of Sciences at Berlin.

During the 1950s the observatory was extended significantly. Since then there are several one- to two-story buildings with laboratories and workshops, attached domes for observing equipment, and green spaces between buildings. Until the early 1960s, new instruments were being purchased and the number of scientific staff increased considerably. In 1960 and 1961 two astrographs, each with 40 cm aperture, came into operation. Sonneberg was a candidate site for a 2 m Schmidt telescope (Germany's largest telescope), but in 1960 this was assigned instead to Tautenburg near Jena for a new observatory there – today's Thuringian State Observatory.

After the Berlin Wall was built on 13 August 1961, the Sonneberg Observatory found itself inside the restricted border area and was almost inaccessible to visitors and scientists unless they lived within the Sonneberg restricted zone. The observatory was therefore no longer competitive in international research. As part of a reform of the Academy of Sciences in 1967, the observatory was placed under the control of the Institute of Astrophysics of the Academy. Further plans called for the dismantling of all instruments in 1969, relocation of scientific staff and site closure. The new scientific director Wolfgang Wenzel prevented this through his intervention. An imposed ban on observing with the large instruments was initially ignored and reversed in the mid-1970s. The scientific work and long-term research programmes then continued until the end of the GDR in 1989, when Sonneberg observatory had 36 employees.

The most critical time for the observatory began with German reunification in 1990. Initially, it became the property of the state of Thuringia. After evaluation of the research facilities across Thuringia, the Tautenburg observatory with the 2 m Alfred Jensch Telescope obtained the status of state observatory, where public research funding would be targeted. Sonneberg observatory was scheduled to close in 1991. Thanks to the efforts of the then head of the observatory, Woldemar Götz, the closure was postponed until the end of 1994; the observatory would continue to operate with ten employees as a branch of the Thuringian State Observatory Tautenburg. In 1992, the new director of the observatory, Hans-Jürgen Bräuer, together with Cuno Hoffmeister's nephew Klaus Hoffmeister, founded the support association Freunde der Sternwarte Sonneberg e.V. (Friends of the Sonneberg Observatory). The observatory reopened on 9 November 1995. Between 1995 and 2003 it was a municipal institution and received financial support from the city and district of Sonneberg, as well as from the states of Bavaria and Thuringia. Under the leadership of Constanze la Dous, four employees launched a five-year project to continue the internationally recognised Sonneberg observing programmes and to digitise the world's second largest astronomical plate collection.

In 1998, an astronomy museum was set up in the observatory's oldest building. This welcomes around 5000 visitors annually. The establishment of the museum was made possible in part through a job creation programme. When this ended in December 2000, funding was received once more from the district and the town in order to be able to continue working until 2002. The project obtained a final extension until the end of 2003.

Since 1 January 2004, the observatory is operated by the Zweckverband Sternwarte Sonneberg (Support Association Sonneberg Observatory) and the company 4pi Systeme – Gesellschaft für Astronomie und Informationstechnologie mbH (4pi Systems – Society for Astronomy and Information Technology Ltd). The company had been founded in 2000 by former employees of the Sonneberg Observatory. In January 2004 it had twelve employees; it develops software for the operation of astronomical telescopes. 4pi Systeme, with the support of the Friends of the Sonneberg Observatory, also operated the scientific facilities of the observatory. The astronomy museum was run by the Support Association, so that the astronomy museum, lecture hall and the observatory's instruments could be used for exhibitions, guided tours and lectures. Since the beginning of 2016, the museum and its public relations work are run by the Astronomiemuseum e.V.

Scientific work

The observatory worked mainly in the following areas:

Research into variable stars, comets, meteors, meteor showers, and other extraterrestrial objects.
Two long-term research programmes of the Sonneberg Field Patrol and Sonneberg Sky Patrol.
The development and construction of scientific instruments to conduct celestial observations and to evaluate the results.

The Sonneberg Observatory has the second largest archive of astronomical plates in the world, which is a valuable source of information for variable star research. It includes over 270,000 photographic plates that show the changes in the northern sky over more than 70 years. The archive also contains around 5,000 photographic plates of the southern sky that Cuno Hoffmeister took between 1926 and 1959 on several expeditions to Bolivia and South Africa. More than a quarter of all known variable stars in the Milky Way were discovered using the Sonneberg plates. Most of the plates were taken as part of the Sonneberg Field Patrol and the Sonneberg Sky Patrol. The long-term Field Patrol was started in 1924 by Cuno Hoffmeister and ran until 1995. The Sky Patrol is based on Paul Guthnick’s idea of monitoring the entire northern sky using astrophotography. These programmes have been running since 1926 until today. Since unexposed photographic plates became unavailable in 1997 onwards, sky monitoring was switched to film material. The historical photographic plates are available for scientific research and since 1992 are being digitized. This work continues to this day and is being carried out by employees of 4pi Systeme. A project to significantly improve the signal-to-noise ratio of some of the already digitized plates using the pixon method ran until 2005 jointly with the Technische Universität Ilmenau.

Instruments

The initial main instrument of the observatory, in 1926, was a 135 mm refractor with various cameras. In 1938, an astrograph with a 400 mm aperture and 1600 mm focal length was used as the new main instrument, but this was dismantled in 1945. The observatory now houses two Cassegrain reflectors with 60 cm aperture, a Schmidt telescope with 50 cm aperture and two astrographs, each with 40 cm aperture. In addition, and as a long-term alternative for the sky patrol that has been carried out with astrographs since 1926, a CCD camera has been used in conjunction with a wide-angle lens since 2002. The camera is a MultiMega CCD camera (manufacturer: OES - Optische und Electronische Systeme) with a 7k × 4k chip (chip area: 84 × 48 mm, made by Philips) and with a water-cooled Peltier element.

The 1926 refractor and the 60 cm Cassegrain reflector are now available to visitors as part of public observing evenings.