The McMath-Pierce Solar Telescope is the world's largest solar telescope. It opened in 1962 on Kitt Peak, Arizona, and is a facility of the National Solar Observatory. It comprises three telescopes in one – the main, east auxiliary, and west auxiliary systems – that can be used concurrently or independently. The main telescope is housed in an inclined shaft, 152 meters long, that runs parallel with Earth's axis. A heliostat mounted on a 33.5-meter-high tower reflects sunlight down this shaft to a 1.6-meter mirror, about 50 meters below ground level, which reflects the light partway back up the shaft to a flat mirror. From the flat mirror, the light travels vertically down to form an image of the Sun 85 centimeters wide in a subterranean observation room. The telescope is named after American solar physicists Robert McMath (1891–1962) and A. Keith Pierce (1918–2005).