Cerro Pachón

Observatories

Starting in 1964, Cerro Morado and Cerro Pachón were the subject of routine observations of seeing conditions. Known as astronomical seeing monitors (ASM), these were operated by the Carnegie Institution of Washington.

In 1989, site planning was begun by the National Optical Astronomy Observatory to select two sites for a proposed pair of 8 m telescopes, one in the northern hemisphere and the other in the south. The first telescope would be located on Mauna Kea in Hawaii, while the second would be at the Cerro Tololo Inter-American Observatory (CTIO), possibly on Cerro Pachón. It is the highest peak within the CTIO boundary, rising some 500 m higher than the nearby peaks of Cerro Tololo and Cerro Morado. A site survey showed that the seeing conditions on Cerro Pachón rivalled that on Mauna Kea, and it was chosen as the site for the Gemini South observatory. First light for the newly-commissioned telescope took place on January 18, 2002.

The Andes Lidar Observatory was constructed on Cerro Pachón by the University of Illinois and saw first light in 2009. This is an upper atmosphere facility that is supported by the National Science Foundation. It uses ground-based remote sensing instruments to study the atmosphere, particularly between altitudes of 80 to 110 km.

The Vera C. Rubin Observatory is located on El Peñon (The Rock), the southernmost summit of Cerro Pachón. It was selected as the site for the Large Synoptic Survey Telescope in May 2006, beating out the alternative Sierra de San Pedro Mártir site. First light images were released 23 June 2025.

Gallery

File:Cerro Las Tortolas indistance incenter.jpg|Wide view observatories from the air, including Cerro Pachón. In the distance are the Andes File:Telescope Silhouettes at Cerro Pachón.jpg| A night view of the Gemini South, the southern half of the international Gemini Observatory on Cerro Pachón with the Milky Way and streak of light left by a meteor in the background. File:Vera C. Rubin Observatory under construction.jpg|Vera C. Rubin Observatory, showing the access road atop Cerro Pachón

References

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References

1. (November 2011). "Results from the LSST site monitoring". Astronomical Site Testing Data in Chile.
2. Feder, Toni. (2006). "Chilean Site Chosen for LSST". Physics Today.