An observatory near Tucson, Arizona, USA, site of the largest collection of optical telescopes in the world. The largest is the 4-m/158-in Mayall reflector (1973). Kitt Peak is part of the National Optical Astronomy Observatories, which also includes the Cerro Tololo Inter-American Observatory in Chile, operating a similar 4-m reflector to that at Kitt Peak, and the National Solar Observatory, which has instruments on Kitt Peak including the McMath-Pierce solar telescope, the world's largest telescope for observing the Sun.