The VTT and the GREGOR are operated by four German institutes: the Astrophysikalisches Institut Potsdam, the Kiepenheuer-Institut für Sonnenphysik (Freiburg, chair), the Max-Planck-Institut für Sonnensystemforschung (Lindau), and the Universitäts-Sternwarte Göttingen. The telescope is used for scientific observations from mid April through mid December. Typically 30 to 40 observing campaigns are carried out every year.
An audiovisual about the telescope is available here.
In the early seventies, the 40cm Newton-telescope, built at the Kiepenheuer-Institut, was installed at the Observatorio del Teide.
In 1982, the Federal Republic of Germany joined the international Agreement on the Cooperation in Astrophysical Research between Spain, Great Britain, Sweden and Denmark.
Construction work for the German solar telescopes started in 1983, including the Vacuum Tower Telescope (VTT), and the Gregory-Coudé-Telescope (GCT) of the Universitäts-Sternwarte Göttingen. The VTT has been developed at the Kiepenheuer-Institut in Freiburg during the mid seventies. The telescope was installed in 1986 and the scientific operations started in 1988. Since then, the VTT has been constantly improved and has been the ?working horse" for our researchers. The GCT was put into operation in 1985 and was finally dismantled in 2002, in order to make room for the new 1.5m-telescope GREGOR.
The VTT is a classical solar telescope: two coelostat mirrors at the top feed the sunlight into the telescope which spans 10 floors. The primary mirror has a diameter of 70 cm and a focal length of 46 m. The main advantage of the coelostat system is the non-rotating solar image in the laboratory. The VTT offers several spacious optical laboratories for all kinds of optical setups. Some of the laboratories are used for permanent installations, but there is always room for specialized or dedicated instruments.
Since 1998 an adaptive-optics system has been developed at the KIS. The main components of the system are a Shack-Hartmann wavefront sensor with 36 sub-apertures, a deformable mirror and a high-speed digital camera. A closed-loop bandwidth of about 70 Hz is achieved. Since 2003, the AO system is permantly installed and available to all focal plane instruments. At present, a multi-conjugated adaptive optics system is being developed at the VTT.
The VTT is equipped with several focal plane instruments for the observation of objects and physical processes on the solar surface. Some of these instruments have been developed at partner institutions: Echelle Spectrograph (KIS, 1988), MSDP (Obs. Meudon, 1989), Fabry-Pérot Interferometer (USG, 1992), Triple Etalon Solar Spectrometer (KIS, 1997), Tenerife Infrared Polarimeter (IAC, 1998), Polarimetric Littrow Spectrograph (KIS + HAO, 2001).
The VTT instrumentation is designed for high-quality measurements of plasma flows and magnetic fields. Some instruments can be combined for simultaneous observations in different parts of the solar spectrum, from the near infrared to the near UV. This possibility is a unique feature for a solar telescope and allows to reveal the three-dimensional structure of the solar atmosphere. With the help of adaptive optics and suitable image reconstruction techniques it is now possible to observe physical properties of small-scale objects on the solar surface with sizes of only 150 km, at the theoretical limit of the telescope. The pictures show a small region of the solar surface with two dark pores. The panel on the right shows how the plasma moves: red is downward motion and blue is upward, the total range is from -1.4 km/s to +1.4 km/s.