Hamburg Observatory - Overview:
Buildings & Telescopes

The Equatorial is the oldest telescope still erected in Bergedorf. It is a refractor with aperture diameter and focal length of 26cm and 3m, respectively.

The term `Equatorial' has two meanings. In a broader sense, it denotes a refractor telescope with parallactic mounting (i.e. with the axes adjusted to the equatoreal system). The expression arose at the end of the 18th century with the first parallactically mounted telescopes to distinguish them from instruments mounted in the azimuth system (meridian telescopes, passage instruments etc.) which were more common at that time. In a narrower sense, an equatorial is a parallactically mounted telescope equipped with large, fine-scaled position circles and readout microscopes to allow direct position determination outside the meridian by measuring right ascension (or hour angle) and declination differences. The Hamburg Equatorial is the largest of its kind ever built. However, the accuracy of the positions determined with this instrument was noticeably inferior to that obtained with meridian measurements. Instrument developmend had run down a dead end street.

Hamburg's Equatorial was completed in 1867 by the Hamburg firm A. Repsold & Sons, and set up in a tower built in 1855, with iron dome, at the northern side of the old observatory building at the Millerntor. The two-lensed objective was made by the Munich firm G. and S. Merz. In 1870, a second objective was manufactured for the telescope by Hugo Schröder, a Hamburg optician. It proved, however, to be of lower quality than the Merz objective.

During its time at the Millerntor, the Equatorial was used primarily for visual observations of comets and asteroids. In addition, large programs for position determination of `nebulae' were carried out, although nobody seemed, at that time, to know the exact nature of these objects.

The telescope was taken down in May 1908, and re-erected at its new location in Bergedorf after thorough checks by Repsold & Sons. A new building had been set up in the south east of the observatory ground, but the old dome (6m diameter) could be reused. Merely the lids that covered the slit were replaced by a slider. To ensure easy handling, a wooden observing chair was placed in the dome which can be moved around the telescope, as well as up and down, by ropes - without the astronomer having to rise.

The Equatorial was used in its first years at Bergedorf by K. Graff for manifold visual observations of planets, comets, and variable stars. After the end of World War I, with all the new, and bigger, telescopes at the observatory working, it became quiet about this instrument. It is mentioned only occasionally in the annual reports of the twenties and thirties.

A late bloom for the Equatorial came about after World War II, at the hands of the impassioned amateur astronomer Max Beyer. Between 1946 and 1977, he observed comets and variable stars in nearly every clear night. His visual observations are exemplary for their continuity and exactness; they were regularly published in the German journal `Astronomische Nachrichten'. Until quite recently, Beyer was the observer with the most visual comet estimations worldwide. Besides this, the Equatorial was occasionally used for public showings.

The telescope is still in working order. It is little used for observations, though, because surrounding trees limit the accessible sky to a small window near the zenith. Moreover, since March 1996 the dome cannot be opened due to a mechanical failure of the shutter.

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