Telescope

 

Laboratories and light path in the Einstein Tower

 

The Einstein Tower houses a telescope for observations of the Sun. Originally, the telescope was built to prove one of the predictions of the theory of general relativity, namely that the lines in the spectrum of the Sun should be shifted due to its large gravitation. Einstein (1879-1955) supported construction and operation of the telescope although he never worked with it himself. The scientific layout of the telescope was done by Erwin Finlay Freundlich (1885-1964), who also observed with it after its completion.

The central part of the telescope is a lens of 60 cm diameter and a focal length of 14 m. This yields a solar image of about 13 cm diameter. In orer to avoid moving the whole telescope, there is a coelostat in the rotatable dome which follows the path of the Sun across the sky. The coelostat consists of two flat mirrors, one of them turns around an axis parallel to the Earth's axis following the Sun and the other reflects the solar light into the vertical telescope.

From the telescope, the light is guided to a spectrograph. The spectrograph is equipped with a collimating lens (Littrow lens) of 12 m focal length. The grating has a size of 42 cm x 32 cm and 632 grooves per millimeter. At a wavelength of 600 nm, a spectral resolution of 0.56 pm is achieved. Part of the light can be sent to a second smaller grating to simultaneously observe in a second spectral line. The spectrograph can also be used to analyse the polarization of the solar light which is correlated to the strength and direction of the magnetic field on the solar surface. To keep the thermal environment of the spectrograph stable, it is placed in a thermally insulated room deep inside the building.

Coelostat mirrors of the Einstein Tower

 

 

The gravitational redshift of the spectral lines could not be proven as planned because the outer layers of the Sun are in turbulent motion producing a variety of line shifts as well. The effect, however, was proven by use of the Moessbauer effect in a laboratory experiment.

Measurements of magnetic fields in sunspots were carried out over many years. Such research observations can now be made under much better conditions from the Observatorio del Teide at Tenerife using the GREGOR and VTT telescopes.

Test of optical components in the lab of the Einstein Tower.

 

Current works in the laboratory of the Einstein Tower deal with preparations of new instruments and tests of components for the modern telescopes, but also include experiments for the students of astrophysics at the Potsdam University.