The Vacuum Telescope

The Vacuum Telescope. . , The accompanying picture shows a cross section of the solar vacuum telescope. This facility, built in 1973, is used to study the evolution of sunspots and other solar magnetic fields. It is operated daily by the National Solar Observatory (NSO) in partnership with NASA and the National Oceanic and Atmospheric Administration. On top of the tower, two flat mirrors track and reflect sun light downward through a window into a vacuum tank. This vacuum tank extends most of the height of the building. Near the bottom of the tank, a curved mirror focuses light back up to another flat mirror which sends the light down and out of the tank through an exit window. , The focussed image of the sun is about 33 cm in diameter. By running most of the optical path in a vacuum The distortions of the image quality by air are avoided. The final image shows details on the Sun smaller than the state of Arizona. The position of the solar image is controlled by a secondary set of lenses and mirrors which provide a smaller image to a guiding mechanism. , Beneath ground level, a large spectrograph spreads the sunlight into its various composite wavelengths or colors. The spectrograph feeds this light to instruments which measure the magnetic field strength and velocity of the visible surface of the Sun. Such measurements are used to predict and help understand solar activity which affects space and earth.