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Einstein Tower

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Einstein Tower

The Einsteinturm in Potsdam, Germany
Named after	Albert Einstein [1]
Organization	Leibniz Institute for Astrophysics Potsdam [2]
Observatory code	042
Location	Telegrafenberg, Potsdam-Süd, Germany[1][3]
Coordinates	52°22′44″N 13°03′49″ECoordinates: 52°22′44″N 13°03′49″E
Established	1924 [2]
Website	www.aip.de/de/forschung/forschungsschwerpunkt-kmf/cosmic-magnetic-fields/sonnenphysik/optische-sonnenphysik/einsteinturm
Location of Einstein Tower
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A rear view of Erich Mendelsohn's Einstein Tower

Zeiss-type Coelostat in the dome of the Einstein Tower. On the right is the heliostat. On the left, a mirror which reflects the beam of light down the tower. The mirrors were covered with protection caps when the photo was taken.

Equipment and initial research focus

In 1911 Einstein published the initial version of his innovative General Theory of Relativity. One of the predicted effects according to the theory was a slight shift of spectral lines in the sun’s gravitation field, now known as the red shift. The solar observatory in Potsdam was designed and constructed primarily to verify this phenomenon.
The Mount Wilson Observatory in California, the first tower telescope worldwide, was the model for the facility designed by Freundlich. In tower telescopes a coelostat (a system with two deflecting mirrors, pronounced "seelostat") at the top of a vertical construction directs light down to an objective. The actual lens system is rigidly integrated into the construction. The mirrors at the top are movable and only these small lightweight instrument components are needed to track the sun. Because of the vertical arrangement, air turbulence near the ground has virtually no effect.
In the Einstein Tower the construction containing the optics consists of two wooden platforms, each six m high, placed one above the other. The telescope has a lens objective of 60 cm diameter and focal length of 14 m. Rooms for observations and measurements are located at the base of the tower. In California the lab rooms are under each other; in Potsdam they are arranged horizontally. Another rotating mirror directs the sunlight to the spectrograph lab located in the basement behind an earthen wall on the southern side of the tower. It is about 14 m long and thermally insulated. Here is where the light is split up into its spectral components and analyzed. This design of a horizontal laboratory wing led to the elongated profile of the entire facility.
Soon after research started at the site, it became evident that the proof sought would be harder to obtain than originally anticipated since the minimal shift of spectral lines was obscured by other solar influences. The reason was atmospheric turbulence on the solar surface. However, Einstein and Freundlich had from the beginning not only been interested in the specific problem of the red shift, but had also intended basic research in solar physics, and the laboratories were so designed that new equipment could be installed without difficulty. The turbulent behavior of the outer solar atmosphere soon became the primary subject of research at the Einstein Tower. The red shift could be proved only in the 1950s after it became possible to precisely analyze the complex disturbances of the solar atmosphere.

Main sights

Einstein Sculpture

In the tower’s entrance area there is a bronze bust of Einstein which was originally located in one of the rooms of the observatory. After the Nazis' anti-Semitic dictatorship began in 1933, the Einstein Tower lost its name and status as an independent institute. Pictures of Einstein were removed and sculptures were supposedly melted down. However, after 1945 it was discovered that staff members had rescued the portrait bust now to be seen at the base of the tower by hiding it behind crates in the spectrograph lab. As a hidden homage to Einstein a single stone (German: 'ein Stein') was placed where the bust had stood, a tradition that is still kept (the stone is regularly stolen though and has to be replaced).

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