McMath–Pierce Solar Telescope, Solar telescope at Kitt Peak National Observatory, United States
The McMath-Pierce Solar Telescope is a solar observation instrument at Kitt Peak National Observatory in Arizona that captures sunlight with a heliostat and directs it down through an underground concrete shaft to a primary mirror. The visible structure rises as a slanted tower above the observatory grounds, housing both the upper shaft and the heliostat system at its top.
The telescope was completed in 1962 and held the title of the world's largest solar instrument for nearly 6 decades. In 2019, the Daniel K. Inouye Solar Telescope in Hawaii took over that role.
The building was designed by American architect Myron Goldsmith and engineer Fazlur Rahman Khan, who treated scientific function as the main design principle. Visitors notice right away that the slanted tower is not an artistic choice but a direct result of how the instrument needs to receive sunlight.
The observatory sits on a mountain in the Sonoran Desert, and reaching it takes about an hour from Tucson. Mornings are generally clearer than afternoons, when desert clouds tend to build up around the summit.
The underground shaft runs in two sections, first dropping about 110 feet (33 meters) vertically and then continuing about 200 feet (61 meters) horizontally beneath the mountain. Keeping the mirror underground protects it from temperature swings that would otherwise distort solar observations.
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