Großer Refraktor (Great Refractor)

Overlooking the city of Potsdam, Telegrafenberg (Telegraph Hill) has been a hotbed for astronomy since the 19th century. An observatory was founded in 1878, and the construction of the Großer Refraktor (Great Refractor) furthered the scientific endeavors at this site. Completed in 1899, the massive double refractor telescope featured two openings, one measuring 80 cm and the other 50 cm. Unlike most of its contemporaries, this telescope was made specifically for astrophysical studies, arguably making this telescope and the surrounding area the birthplace of a new field. 

Astronomy focuses primarily on the observation of stars, cataloging their brightness, position, and movement across the sky. Astrophysics combines these observations with physical principles, also considering the composition of stars and the physical processes happening within them.

Most telescopes built around the time of the Großer Refraktor were designed for observation, having either an eyepiece for the astronomer to look through or a photographic plate holder. But the Großer Refraktor was designed to hold one of the first spectrographs, which can measure specific properties of light.

The most famous discoveries done with this telescope are that of the interstellar medium by Johannes Franz Hartmann in 1904, along with the Hartmann test, a special grid that one placed on the telescope to measure the quality of the air and the lens. This technique is still used today in adaptive optics to improve images.

The telescope and building were badly damaged in 1945 by bombing during World War II. The building was repaired and modernized in the 1950s, but the telescope ceased operations in 1968. The telescope and its dome-shaped building opened as a public monument in 2006 after undergoing restoration. It is part of the Albert Einstein Science Park, along with the nearby Einsteinturm.