Potsdam Great Refractor, Historic refracting telescope on Telegrafenberg, Potsdam, Germany.
The Potsdam Great Refractor features two permanently connected tubes with diameters of 80 cm and 50 cm, housed within a 21-meter rotating dome weighing approximately 200 tonnes on Telegraph Hill.
Inaugurated in 1899 in the presence of German Emperor Wilhelm II, this telescope facilitated Johannes Hartmann's groundbreaking 1904 discovery of the interstellar medium through spectroscopic observations of calcium lines.
Recognized as an architectural heritage monument since 1983, the Great Refractor represents Germany's significant contributions to late 19th-century astronomical research and international scientific collaboration efforts.
Visitors can participate in guided tours and observation evenings organized periodically by the maintenance group, with access coordinated through the Albert Einstein Science Park on Telegrafenberg.
This instrument remains the fourth-largest refracting telescope globally and houses thousands of archived photographic plates used for continued software-driven astronomical research and historical documentation.
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