A complex of astronomical telescopes and instruments located 70 km east of La Serena, Chile, at an altitude of about 2,200 m on Cerro Tololo mountain. Founded in 1963 and part of the U.S. National Optical Astronomy Observatories, its main instrument is the 4-meter Blanco Telescope, opened in 1976, that is the southern twin of the 4-m instrument at Kitt Peak National Observatory. On a peak 10 kilometers to the southeast is the 8-meter Gemini South telescope.
