The Equatorial

The Equatorial is a refracting telescope with a 26cm objective lens diameter and a focal length of 3m. It is the oldest telescope still in operation in Bergedorf – it had already been working in the old observatory in the city of Hamburg and moved to Bergedorf with the opening of the new observatory in 1909. The company A. Repsold & Söhne supplied the instrument in 1867, while the objective lens was produced by the company G. and S. Merz in Munich.

The name “Equatorial” refers to the mounting, which has one rotational axis along Earth’s rotation axis within the equatorial system of the Earth (equatorial or parallactic mounting). This was special at the time and allows adjustment of the telescope by rotating only one axis. Additionally, the instrument was equipped with big reference circles for the measurement of positions. A characteristic feature of this telescope is the wooden observer´s chair, which rotates on rails in the dome. It permits the astronomer to assume a comfortable position while observing.

The Equatorial is typical of classic astronomical instruments in the 19th century. At that time, the measurement of star positions was the primary task of observatories.

 

Fig. 1: The Equatorial

Fig. 2: The dismantling of the Equatorial dome at the Millerntor in 1908

 

Light pollution

Light pollution was the main reason for the transfer of the observatory from the centre of Hamburg to Bergedorf. Nowadays, astronomical observations on the Gojenberg are equally impaired due to neon signs and illuminated buildings, as well as street and outside lighting. Even far from the centre of Hamburg, one can see only a few hundred stars against the illuminated background, instead of the thousands of stars and the Milky Way visible under a completely black sky. This is why today the astronomers of Hamburg Observatory rely on observational data obtained by external telescopes. Excessive illumination affects not only astronomical research though. Many animals, for example insects and migratory birds, as well as humans, suffer from nights turned to artificial days. Optimising illumination would convey not only ecological and health benefits, but also save money.
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