Hamburg Observatory - Overview:
Buildings & Telescopes

The Oskar-Lühning Telescope is the largest instrument at Hamburg Observatory, and currently the second largest telescope in Germany. It is a Ritchey-Chretien system with 1.20m aperture and a focal length of 15.60m in the Cassegrain focus. Built in 1975, it is also the youngest telescope at the observatory. Building and mounting, however, date back to 1954. They housed originally the Big Hamburg Schmidt Telescope. The building also houses a metallizing facility, for large mirrors which is still in operation today.

Its existence owes the telescope to the foundation of Bergedorf's headmaster Nikolaus Lühning. His son Oskar intended to study meteorology and astronomy, but at the beginning of World War II he had do join the Wehrmacht (army), and was lost in Russia since 1943. With no other heirs, the Lühnings left their fortune to the university to be spent - according to their son's intentions - on the advancement of astronomy.

In the mid-seventies, the plan was realised to relocate the Big Hamburg Schmidt Telescope to the Calar Alto Observatory (Spain). The telescope could no longer be effectively used: its large focal ratio made it too sensitive of the bright night sky of Hamburg. Because of the different geographical latitude of South Spain, a new mounting was required. The telescope was taken down in June 1975, while the fork mounting remained in its dome in Hamburg.

For some time, Hamburg Observatory had intended to obtain a modern 1.3m telescope for spectroscopic and photometric investigations of single objects. The university, though, had been unable to provide the neccessary means. Now in 1974, thanks to the Lühning-Foundation and additional means from the Hamburg Senate, the new telescope could be ordered from Grubb-Parsons (Great Britain). Near the end of 1975, the instrument was set up in the former Schmidt dome in the old fork mounting. It was named Oskar-Lühning-Telescope in honour of the son of the founder. Due to its smaller focal ratio it is less strongly affected by light pollution than the Schmidt telescope.

After some adjustment problems were solved, the telescope was used until the mid-eighties, primarily for photoelectric measurements. Further works included (among other studies) determinations of angular diameters of planetary nebulae, and spectroscopic observations of novae and Beta - Cephei stars. The latter purpose made use of a grid spectrograph, bought in 1973 with money from the VW foundation, which unfortunately proved to be technically insufficient.

Since 1994, after several years without scientific observations, the Oskar-Lühning Telescope is occasionally used to obtain CCD images (e.g. Hale-Bopp). The electrical and/or mechanical parts of the mounting, by that time more than 40 years old, caused occasional problems, and the dome seeing is often less than optimal, because of the heated yet badly isolated office rooms in the storeys below. In 1998 the telescope was closed for reconstruction. At first only mechanical improvements were planned, but later one realized, that the telescope - if equipped with a powerful CCD or a modern star spectrograph with high resolution - could be successfully used for a variety of observational purposes.

The works were completed in 2001, and a modern CCD camera from Apoge with 1024x1024 pixels and a visual field of 5'x5' was installed. The telescope was converted into a robotic telescope, i.e. it can now be fully run via internet from anywhere in the world. With the contruction works Hamburg observatory gained a lot of knowledge which can be used for, e.g. the STELLA project. As a modern telescope it can be used for practice how to work with modern telescopes and it can be presented to the public for explaining how moderen observations are performed. The scientific output will not be very large, since weather and light conditions in Hamburg are poor, but because of the good access the telescope can be used, e.g. for tracing long term variablilty.

German text and images by Matthias Hünsch;   English translation by Kerstin Molthagen