Built in 1973, the solar vacuum telescope 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 sunlight downward through a window into a vacuum tank that 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 focused image of the sun is about 33 cm in diameter. By running most of the optical path in a vacuum, distortions of 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 that provide a smaller image to a guiding mechanism. Beneath ground level, a large spectrograph spreads the sunlight into its composite wavelengths or colors and feeds this light to instruments that measure the magnetic field strength and velocity of the visible surface of the Sun. These measurements are used to predict and help understand solar activity that affects space and earth.