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The Einsteinturm is the outer wrap of 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.
More pictures and sketches of the
Einstein Tower are in the
image archive
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 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 x 32 cm^2 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 properties of the solar light which are intimately
connected with the properties of the magnetic field on the solar surface.
Since the spectrograph reacts rather sensitive on variations of the
temperature, it is placed in a thermally insulated room deep inside the building.
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. Having a more sophisticated
understanding of these motions today, solar physicists are now convinced
that Einstein's prediction is correct.
The most important task of the Einsteinturm in the recent past and
near future is a precise measurement of the magnetic fields in sunspots.
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