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.

Built in 1962, the McMath Solar Telescope was designed by architect Myron Goldsmith and structural engineer Fazlur Rahman Khan of Skidmore, Owings and Merrill's Chicago office. At its dedication, a letter from President John F. Kennedy was read aloud. It was renamed the McMath–Pierce Solar Telescope in 1992 after astronomers Robert Raynolds McMath and Keith Pierce. In 2016 the NSF announced it would divest from the observatory, and a 2018 grant of 4.5 million USD went to AURA for a new visitor center and revitalization.

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 telescope stands at Kitt Peak National Observatory, at an elevation given as 6,885 feet (2,100 m) in Arizona. The instrument is a triple one: the main telescope plus East and West auxiliary telescopes with 0.91 m heliostats beside the main heliostat. The main mirror sits underground at the end of the diagonal shaft, reached from the observing room above.

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.