Architects: Skidmore, Owings & Merrill: SOM
Year: 1962
Photographs: John Owens, Joshin Yamada, Ezra Stroller, Bill Maris
County: Pima
Country: United States
The McMath-Pierce Solar Telescope, completed in 1962 by SOM, is the world’s largest unobstructed aperture optical telescope, designed for studying the sun’s properties. Owned by the Association of Universities for Research in Astronomy, its 50-ton heliostat atop a 100-foot concrete tower directs sunlight down a 500-foot inclined underground shaft with a resolution of 2.50 arcsec/mm. Two auxiliary telescopes with 0.91-meter mirrors operate independently. The underground design stabilizes temperatures, with a steel jacket protecting the heliostat and a cooling system countering solar heat. Named after Dr. Robert McMath and Dr. Keith Pierce, it was celebrated by President Kennedy for advancing solar research.
Completed in 1962, the McMath-Pierce Solar Telescope, designed by SOM, exemplifies architecture created with a highly specific purpose. Primarily intended for the study of the sun’s physical and chemical properties, it remains the world’s largest unobstructed aperture optical telescope.
The McMath-Pierce Solar Telescope, owned by the Association of Universities for Research in Astronomy, features a heliostat weighing nearly 50 tons. Positioned 100 feet above the ground atop a circular concrete tower, the heliostat directs sunlight down a long shaft that extends underground to the telescope’s prime focus, achieving a resolution of 2.50 arcsec/mm.
In addition to its primary 1.6-meter mirror, the McMath-Pierce Solar Telescope includes independent East and West auxiliary telescopes. Both auxiliary telescopes have 0.91-meter mirrors, with focal lengths of 50 and 44, and resolutions of 5.11 arcsec/mm and 5.75 arcsec/mm, respectively.
The telescope’s tube is a 500-foot-long shaft inclined at an angle of 32 degrees to the horizontal. To reduce temperature fluctuations, most of the tube is buried underground, where conditions are more stable than in the air. To protect the heliostat from wind disturbances, a steel jacket was designed as a separate structure, standing independently from the concrete tower as it emerged from the ground.
Exposed to intense solar heat and thermal airflows, the telescope employs a cooling system mounted beneath the exterior cladding to counteract temperature fluctuations. This system operates with a liquid designed to resist freezing even in extremely low winter temperatures. The exterior walls are constructed from copper and concrete, while the interior primarily features steel.
The telescope was named after its initiators, Dr. Robert McMath and Dr. Keith Pierce, and was the largest of its kind in the world at the time. During its dedication in 1962, Dr. Waterman read a letter from President Kennedy, which began:
“The great new solar telescope at the Kitt Peak National Observatory in Arizona is a source of pride to the nation. The largest instrument for solar research in the world, it presents American astronomers with a unique tool for investigating the nearest of the stars, our sun. The project is of exceptional interest to all our citizens…”
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Address: Sells, Pima County, Arizona 85634, United States
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