building the Vacuum Tower Telescope
Construction on a unique, new type of telescope began in 1966. This telescope was the first of a special class of solar telescope optimized to study a sub-region of the Sun in extremely high resolution. The telescope tube was designed to be kept in a vacuum at all times, so that heat from the Sun wouldn't cause turbulent motions in the telescope itself. The main mirror, 1.5 meters in diameter would be kept at the bottom of a 228 foot deep pit below the telescope building, still enclosed in the same vacuum. The entrance window for the telescope would be 136 feet above the ground, making the excavated telescope tube longer than a football field from top to bottom, with most of it being below ground. The image on the left shows the pit for the telescope before the tower was constructed over top of it.
The US Air Force oversaw the construction of the telescope, and the project was finished in just over three years. Costing $3 million dollars to build (about $25 million in 2018), it is still in operation today - a pretty good investment, all things considered!
The vacuum tower telescope concept has since been applied in several other large solar facilities, including the German VTT and the Swedish SST, though no other design quite matches that of the ours! Part of our unique design is the way the telescope "de-rotates" the images of the Sun it produces. Of course, as you have probably heard, the Earth rotates over the course of a day. As it does so, the Sun moves across the sky from east to west - but it also appears to rotate as it does so! To correct this, you have to turn your instruments, including the camera, which isn't always simple. In this case, the entire telescope, over 300 feet long, and weighing in at over 300 tons (600,000 pounds!) was built to rotate in order to track the Sun. The rotating segment includes a 40 feet wide observing table where our instruments are located. The entire 300 ton structure hangs from a one-of-a-kind mercury float bearing located at the top of the tower that keeps the telescope floating in a half-inch layer of mercury. as such, when the telescope isn't tracking, the friction is low enough that the entire structure can be moved by hand!